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Bullet Jump and Seating Depth Reloading Best Practices

Bullet Jump & Seating Depth: Best Practices & Conventional Wisdom

With so many events canceled and stores closed, what a great time to do some reloading! Over the past several weeks, I have been working on a series of posts that I’m very excited to finally share with you guys!

This is the first article in a series related to reloading for precision rifle shooting, but much of what I plan to share could benefit shooters using factory ammo just as much as reloaders – if not more! Over the next few posts, I will be sharing brand new, primary research that I believe you guys will find very interesting. It will primarily revolve around the topic of bullet jump and seating depth, but will also extend into on a few other topics that are important for getting first round hits on targets at long range … but haven’t been explored much in terms of an objective, data-driven approach. I honestly feel like this will be one of my landmark series of articles for 2020, and I’m so excited to share it with you guys!

Part of my goal for PRB is to help new shooters get involved in this sport that I’m obviously very passionate about. I want to be intentional to include new guys in on the conversation. One of my biggest pet-peeves in life is when someone makes someone else feel stupid. I don’t like feeling stupid, and I don’t want anyone else to feel that way either. So, I try to be careful in anything I write to not dive straight into a highly technical conversation and assume everyone knows what we’re talking about. It is very easy to lose new people in jargon and complexity, so this article will lay a foundation for the conversation that we’ll build on in subsequent posts.

This article provides a comprehensive overview of what most professionally published books and reloading manuals suggest about bullet jump and seating depth when it comes to precision rifles. I have a big stack of books on the subject, and I tried to combine the most relevant info from each of them when it comes to fine-tuning the seating depth of your ammo.

What Is “Bullet Jump”?

Bullet jump is basically the distance a bullet travels before it touches the rifling in the barrel. That gap is relatively short distance that typically ranges from 0 to 0.150 inches, although it could be longer in some factory or magazine-fed rifles.

There is a lot going on in a chamber in the tiny window when a round goes off. Factors like whether the bullet jumps 0.010” or 0.070” before it engages the rifling may seem inconsequential but can have measurable impact on the bullet’s flight and group size. There are multiple reasons for that, which I’ll touch on from a high level below. But suffice to say that these kinds of details are especially relevant in shooting disciplines that are pushing the envelope of precision and/or engaging small targets at long distance.

There are two primary ways to fine-tune bullet jump:

  1. Adjust Bullet Seating Depth: When handloading ammo, you can control how far the bullet must jump by adjusting bullet seating depth. However, when a reloader adjusts their seating depth to extend the bullet further out it increases the Cartridge Overall Length (COAL), which may prevent a loaded round from fitting inside your magazine. So, if feeding from a magazine is a priority, you could be limited on how close to the lands you can get.
  2. Adjust Chamber Freebore: Another way to get a bullet closer to the lands and stay within magazine length is to shorten the throat of a chamber. Instead of extending the bullet out of the case towards the rifling by adjusting seating depth, you effectively move the rifling closer to the bullet. The diagram above shows an area labeled as “Throat,” but that distance is also commonly referred to as freebore. Freebore is simply the distance between the neck and where the rifling starts. Let’s say for example that the SAAMI chamber for a particular cartridge calls for 0.180” of freebore. If we use a chamber reamer that only had 0.100” of freebore, that would effectively move the rifling back towards the bullet 0.080”. Okay, technically it isn’t “moving” the rifling – it just means the chamber reamer would leave more of the rifling close to the chamber.

What Every Gunsmith Wish You Knew

Some shooters obsess over freebore (including me at times), and occasionally insist on specific freebore dimension for their barrel, despite a gunsmith’s recommendations. A gunsmith who is brutally honest might say that is one of the most annoying parts of their job. I feel like I should say that out loud on behalf of all my gunsmith friends. And I admit I’ve been an offender at times, too. While freebore can be an important spec, one of the best pieces of advice I can give is this: Find a gunsmith who specializes in precision rifles and has a proven track record of satisfied customers, then tell them what your goals are and how you plan to use the rifle, and finally: trust their recommendations.

What Are Recommended Best Practices When It Comes to Bullet Jump?

Top-Grade Ammo Reloading Book

“It’s pretty well accepted that the shorter the gap, the better, and a long-held, and for good reason, accuracy-enhancing tactic is nearly or completely eliminating jump. The longer the bullet is, and the ‘spikier’ its nosecone, the better it will perform moving toward the lands.” – Glen Zediker, Top-Grade AMMO (Published 2016)

I’ve seen countless quotes like the one above in reloading manuals and books. Top-Grade Ammo is one of the best handloading resources I’ve read, but here is how another popular book explains it:

Metallic Cartridge Reloading Book

“Handloaders can tinker with the bullet-seating depth so as to exceed the listed maximum [cartridge overall length] significantly. Sometimes they can tinker until the bullet comes very close to touching the rifling. This can dramatically improve accuracy. When COAL places the bullet close to touching the rifling, changes of about 0.005 inch can dramatically alter accuracy. … For most hunting rifles and bullets, the optimum bullet-to-rifling jump is usually near 0.020 inch; for target cartridges used in target-chambered guns, the ideal jump can be near zero.” – Mic McPherson, Metallic Cartridge Handloading: Pursuit of the Perfect Cartridge

Handloading for Competition Shooting

Glen Zediker wrote a book entitled Handloading for Competition: Making The Target Bigger, and here are some of the highlights from what it says about bullet jump and seating depth: “Determining the bullet seating depth a rifle likes best is normally ‘fine tuning’ that entices any stray holes to relocate on into the group. Any and every load and bullet responds to seating depth tuning. … How much jump is a good question that has only one answer: whatever shoots best. That may not be the answer anyone was looking for but it’s the right one, and it’s also not always the one we want to accept for various reasons. Most competition rifles will shoot best with bullets seated somewhere between jammed 0.020 and jumping 0.020. … Again, there is no fast rule on the amount of jump a particular combination will prefer, but odds are closer will do better.

Precision Shooting Magazine

One of the most interesting articles I’ve ever read about precision shooting was called “Secrets of the Houston Warehouse.” It was written by Dave Scott and published by Precision Shooting Magazine in 1993. It’s about an accomplished group of Benchrest shooters who conducted experiments in a large warehouse that redefined extreme rifle accuracy. They used the large, controlled environment where the wind never blew, and mirage never shimmered to test virtually every aspect of rifle building and reloading. They were shooting 5-shot groups “in the zeros,” meaning the extreme spread measured 0.099” or less. In fact, they eventually fired 5-shot groups as small as 0.025”!!! Those experiments contributed to many of the best practices Benchrest shooters still use today, and here is what that article says about bullet jump:

“One thing that IS important is that the bullet be precisely seated against the lands. T.J. Jackson reported this fact in the May 1987 issue of Precision Shooting. In a letter to the Editor, T.J. wrote, “… in all our testing in that Houston warehouse … and the dozens and dozens of groups that Virgil King shot in there ‘in the zeroes’… he NEVER fired a single official screamer group when he was ‘jumping’ bullets. All his best groups were always seated into the lands, or at the very least … touching the lands.” – Secrets of The Houston Warehouse, Precision Shooting Magazine

Most published materials on reloading repeat a similar idea. The Hornady Reloading Manual simply says, “In general, the less distance to the bore, the greater the accuracy.

The Practical Guide To Reloading - Long Range Hunting Series by Nathan Foster

Another one of my favorite resources are the books by Nathan Foster, an accomplished gunsmith in New Zealand and author of Terminal Ballistics Research. I’ve read a ton of what he’s written, and Nathan has earned my respect because he has both a practical and data-driven approach. Here is what Nathan says on the subject: “Why seat close to the lands? In our last example Joe read an article where the author stated that for best accuracy, he should be seating close to the lands. Many of you will have heard this statement. Target shooters often go to the extreme and wedge the projectiles right into the lands – but why? The statement ‘because it is more accurate this way’ is not really an explanation. Current research suggests that by pushing the projectile into the lands pressures can be made more consistent from shot to shot.” Nathan later adds that, “The projectile may arrive at the lands slightly off center if it has to travel a long way. In this instance, having the bullet close and concentric to the bore can help minimize potential bullet yaw during ignition. Close seating can also simply be used as a start point for harmonic experimentation. We can test the bullet up close to the lands, then step back if need be, monitoring the effects on accuracy.” So, Nathan has more a pragmatic approach, as expected, where he starts close and then experiments to see what jump results in the best accuracy for that rifle/bullet combination.

Rifle Accuracy Facts by Harold Vaughn

Dr. Harold Vaughn, who is literally one of the greatest researchers of the past 100 years (you should read about him here), concurs with the Nathan’s point about how important it is to get the bullet absolutely centered with the bore. In his book, Rifle Accuracy Facts, which covers his extensive research, he shares how Benchrest shooters desire chambers with minimum clearance in the necks and they also turn the necks of their brass to ensure the bullet is perfectly centered with the bore. Dr. Vaughn goes on to explain, “They also seat the bullets into the lands, which helps center the bullet. However, seating the bullet in the case so that it contacts the rifling in the throat also increase the peak chamber pressure, which is not desirable. Evidently the Benchrest shooters have found that having the bullet centered in the bore is important, and I think they are right. … Seating depth of the bullet in the case has an effect on just how close to the center the bullet will line up. Obviously, the bullet will be centered if it is in complete contact with the lands, however Reference 1 showed that peak chamber pressure decreases if the bullet has a free run before it contacts the lands. Since a minimum in peak pressure for a given load implies minimum bullet distortion, the author prefers a seating depth that will provide about 0.010 inches into the lands in the case of a Benchrest gun with light bullets and about 0.020 inches of bullet free travel before the bullet contacts the lands in the case of a sport shooting heavy bullets.”

The Book of Rifle Accuracy by Tony Boyer

Tony Boyer is the most successful and celebrated Benchrest shooter of all time. He has won several World Championships and was named Shooter of the Year over ten times. In his 2010 book, The Book of Rifle Accuracy, he simply says “When shooting with the bullet into the lands, the lands themselves straighten the bullet without forcing over-travel.” However, Tony goes on to say that bullet shape can affect optimal seating depth, and “There are no hard and fast rules dictating the best seating depth for all bullet/barrel combinations.” But, Tony does say there are some common characteristics of barrels, and when he’s searching for the sweet spot “with a button-rifled barrel such as a Shilen, I would have stopped the search for the optimal seating depth at the 0.012 inches off the jam. … With a four-groove cut-rifled barrel (Bartlein or Krieger), be more patient and keep trying until there is no mark on the bullet at all. Again, I personally do not want to shoot off the rifling so that become my stop point.” So, the guy who has proven several times that he can shoot the smallest groups in the world, says he is always at least touching the lands, and often the bullet is jammed into it.

Extreme Rifle Accuracy by Mike Ratigan

Now and then, 2-3 thousandths change in seating depth can make the difference between average and peak accuracy,” explains Mike Ratigan, Benchrest Hall of Famer and World Champion, in Extreme Rifle Accuracy. Wow, 0.002-0.003 inches in bullet jump can sometimes make the difference! Of the dozen or so published resources I’ve cited so far (plus others), they virtually all suggest testing seating depths in 0.005” increments, meaning most expect that changing the seating depth by just 0.005 inches or less can have a measurable impact on group size on the target.

I could cite even more books, but it seems like there is overwhelming support that if the absolute smallest groups are your highest priority, then minimizing jump seems to be the way to go. Everyone from accomplished scientific researchers to the absolute best-of-the-best, world-champion shooters are convinced that you’ll likely find the best accuracy with 0.020 inches of bullet jump or less.

The One Resource That Suggests Testing Longer

Berger Bullets Reloading Manual

The only professionally published resource I’ve found that clearly recommends testing beyond 0.020” of bullet jump in a precision rifle is from Berger Bullets. In the Berger Bullets Reloading Manual they say:

“What has been discovered is that VLD bullets shoot best when loaded to a COAL that puts the bullet in a ‘sweet spot.’ This sweet spot is a band 0.030 to 0.040 wide, and is located anywhere between jamming the bullets into the lands and 0.150 jump off the lands.

Berger’s VLD bullets are Very Low Drag bullets that have extremely high ballistic coefficients, meaning they are very aerodynamic and ideal for long range shooting, but have been known to be sensitive to seating depth (and probably more precisely bullet jump). Because VLD bullets were known to be very sensitive to bullet jump, Berger apparently performed a lot of research and found that the sweet spot for optimal precision could be as far as 0.150” of bullet jump on some rifles.

Eric Stecker, previously Master Bulletsmith for Berger and now President, provides detailed instructions for how to find the optimal jump in as few of shots as possible in their manual, but they also republished similar information in this article online: Getting the Best Precision and Accuracy from VLD bullets in Your Rifle.

Up Next

Hopefully this post has given us a good fundamental understanding of bullet jump, seating depth, and freebore, as well as a comprehensive view of what conventional wisdom and best practices are from a wide variety of trusted, published sources.

Stay tuned for the next articles which will build on this one and go deeper into some of the latest research on this – which could potentially make us reconsider some of our long-held beliefs on these topics.

About Cal

Cal Zant is the shooter/author behind PrecisionRifleBlog.com. Cal is a life-long learner, and loves to help others get into this sport he's so passionate about. Cal has an engineering background, unique data-driven approach, and the ability to present technical information in an unbiased and straight-forward fashion. For more info, check out PrecisionRifleBlog.com/About.

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48 comments

  1. Great info! I have several of these books including Zediker, Vaughn ( incredible! ) and Poyer.

    I started reloading with Zediker’s book and ran rounds jammed and did get great accuracy.

    After dealing with the powder mess and stuck projo that can result from extracting a live round, jammed, and low neck tension I quit doing that for PRS type shooting.

    Best, and thanks for your efforts and info.

    • Hey, Forest. I appreciate you chiming in. I agree that those are some great books. Nathan Foster’s books are really good, too. I bet if you liked those others, you’d like his work. Of course, there really isn’t anything like Dr. Harold Vaughn’s book, except maybe Modern Advancements of Long Range Shooting. But then again, there aren’t many true research scientists in this field (at least that publish content for the public), and that was the culmination of a literally years and years of work. So I’m not holding my breathe for something like that to come out again. I was honestly just reading through it again the other day. It’s good stuff. Wish I could have met that guy and had a conversation!

      Stay tuned for the next few posts. I bet you’ll find them interesting!

      Thanks,
      Cal

    • Yet another great read. Been waiting on this series Cal! Can’t wait to dive in on the subsequent info!
      Currently working on a .30-06 load (yeah, yeah, I know, that’s an old outdated hunting cartridge- but that’s the point) to attempt to dial in as small a long range group as possible. And I literally am at the point of adjusting seating depth/ jump when this article appears. Thanks for all your hard work. It’s a great resource for us newbies.

      • Ha! Well, timing couldn’t be better for you, Jeff. And don’t feel like you need to apologize for the 30-06 … it’s only taken more animals than just about every other cartridge out there. It’s still a great cartridge when terminal performance is a high priority. It is true that it doesn’t see a lot of love in the long range competition world, but that doesn’t mean it isn’t a great choice for other applications. Just a different set of priorities that you’re trying to balance.

        Hope you enjoy the rest of the posts! I’ve spent a ridiculous amount of time analyzing data, creating visualizations, and crafting the content, but I find this very interesting stuff. Hope you do as well.

        Thanks,
        Cal

      • Thanks for the reply. I really enjoy your articles Cal and have been hoping for this series.
        I should clarify on the 30-06… I’m not a hunter, I’m former military and have always preferred larger bore cartridges. I know there are lots of other calibers that are better suited to the LR niche, and that’s why I chose the 06. Carlos Hancock took many of the 2-legged variety from some pretty impressive distances with an 06. I guess when I started this rifle build I kind of chose the 30-06 as a personal challenge to see just how far I could accurately stretch it out. Factory rifle zero’d at 150 with well under a 1/2″ 5 round group so far. Got a long way to go yet.

  2. Anyone who wants to learn the most efficient method to reload and find the best accuracy node fast should read this article by Dan Newberry who invented the OCW method of reloading.

    http://optimalchargeweight.embarqspace.com/ocw-instructions/4529817134

    In addition, for those who are more computer literate, they need to look into the computer software QuickLoad. This software can help you zero in on the accuracy node.

    https://www.accurateshooter.com/gear-reviews/test-quickload-review/

    A combination of the two, which is to use QuickLoad to narrow the load and then use OCW to finalize load and seating depth is about as good as it gets.

    • You’re absolutely right, Joseph. I actually will talk a little about Dan’s OCW method in a subsequent post in this series, but those are both good things to use. I have personally used QuickLoad a lot more recently than I have in the past, and it’s a great resource.

      Great tips! Thanks for sharing.

      Thanks,
      Cal

  3. Cal,
    Given that less bullet “jump” is usually better, AND that a chamber cut to minimum SAAMI specs also means that bullet is closer to being centered on the bore, would it be a good thing for precision rifles to have these specs posted?
    Naturally any jump and chamber size specs would have to be based on the maximum SAAMI cartridge overall length (COAL) and chamber dimensions otherwise they would be meaningless in trying to compare one maker’s rifle to another.
    So in this discussion on bullet jump to the lands I think we must also keep chamber size in mind. Yes, after the First firing there is a “custom fit” to the chamber, making a sloppy chamber a bit less important but having a “snug” chamber (in SAAMI terms) seems better from the start as well as for case life.

    Most commercial precision rifle makers must follow SAAMI specs for liability reasons and custom chambering that go beyond these specs is another story altogether.

    • Hey, Eric. Thanks for the comments. I follow what you’re saying about cutting a chamber to minimum specs would theoretically cause a bullet to more naturally align with the center of the bore, but I’m not sure what specs you’re suggesting be posted. I might think you’re talking about what the bullet jump would be for a particular chamber and ammo loaded at max SAAMI COAL, but even then the geometry of the particular bullet you are using would impact what the jump would be. Bullet jump is more closely correlated to Cartridge Base To Ogive (CBTO) and not Cartridge Overall Length (COAL), which is the cartridge base to the tip of the bullet. So it seems to me that bullet jump depends on too many factors to provide helpful specs, including chamber reamer dimensions (like you mentioned), specific bullet design being used, leade angle of the rifling, etc. Of course, I could be misunderstanding what you were suggesting there, so please clarify if that’s the case.

      I do agree that most commercial rifle makers have to follow SAAMI specs, which can make tuning bullet jump a little more difficult for reloaders. Sometimes you might run out of case neck or would have to exceed magazine length on a cartridge in order to reach the lands. It’s definitely a hassle and something you might have to consider if you’re using a factory rifle. It’s not always a problem, but often is with long, heavy-for-caliber, high-BC bullets that are popular for long-range shooting. If you use shorter, lighter-weight bullets in a factory rifle, you can often have a little better luck reaching the lands, because the dimensions of the bullet are different.

      Thanks,
      Cal

    • There are a couple of things to keep in mind when talking about chamber specs and jump distances.

      If you go for minimum SAAMI specs, you will be forced to seat the bullets deeper than say if your chambers are longer. It of course depends on whether your final use will be single load or off a mag. If single load, the only factor is enough neck grip on the bullet to prevent it from falling out and also alignment i.e. concentricity. If you are using a mag, then max COAL would be that it fits in the mag.

      One reason to avoid minimum SAAMI specs is the deeper you seat the bullet into the case, the smaller the case volume and less space for more powder and at least for the same powder weight, the higher pressure with less volume.

      In terms of jump distance, one reason to avoid distances significantly shorter than 10 thousand is there are a lot of things that can affect accurate/consistent bullet seating, and 10 thousands gives you some grace to avoid jamming when you think you are seating. Very bad if you are at max charge.

  4. Did you poll seating depths in your what the pros use for different chamberings? I would be interested to see the jam vs jump spread in PRS. I currently shoot a dasher and it, like all my other rifles, prefers the bullet jammed. However, I am afraid of dumping powder in my action during a match.

    • Hey, Brad. Great question. I didn’t ask that on my top shooter survey, but am considering asking that in the future. I did ask a couple of the top PRS and NRL shooters what they did, and plan to share their tips in subsequent posts … so stay tuned!

      I would suspect that there aren’t many shooters that jam bullets in PRS-style competitions, for the same concerns you mentioned. In these kinds of matches there are times where you have to remove an unfired round from your chamber, and if it’s jammed the bullet could stay in the rifling and gun powder could be dumped into your action. That is too big of a risk for the theoretical or incremental benefit you might get from jamming it into the lands. It’s just a different game than some other shooting disciplines, and that is one of the things you may have to think about differently because the structure of the matches and priorities are different.

      Thanks,
      Cal

  5. Realy like your write ups Look forward to your articles to come

  6. I love the principles explored here, but take the opportunity to point out some anomalies that I may well have missed in the conversation (my apologies if I have).

    Most of the advice is perhaps correctly focused on traditional jacketed bullets regarding jump, given that some competitions still don’t allow monolithic bullets in some countries. Fair enough.
    Should these dimensions be applied to copper bullets however, disappointment can be assured. Copper bullets usually like a jump of 0.9 – 1.3 mm or 35 – 55 thou (I say usually – there will always be an exception pop up somewhere!) for best performance. This of course dependent on the alloys and coatings used.
    Whilst most find the use of copper bullets either a novelty or outside their scope so to speak. new benchmark standards are being set with copper bullets now on a regular basis around the world. Use of traditional product settings with copper bullets will achieve a similar result as would be expected by putting diesel in your petrol. The results aren’t pretty.

    • Very interesting, Stephen! I haven’t even thought about that. I use solids in my 375 CheyTac, but I’m using a Desert Tech HTI and I can’t get anywhere close to the lands anyway because of their factory chamber dimensions. So I don’t have any experience with it, but I could see how it could potentially be different. I do agree that most of these resources are referring to jacketed bullets. The monolithic copper bullets are a newer things, especially for precision work.

      After reading your comment, I ran out to my shop and pulled my Barnes Bullets Reloading Guide off the shelf to see if they mentioned any recommendations for bullet jump or seating depth, since they have been using solid copper bullets for a while … but I didn’t see anything in there. It only includes very basic reloading tips. But, I did find some info on their website, which seems to be in the same vein as your suggestion:

      “When loading a Barnes TSX, Tipped TSX or LRX bullet, your rifle may prefer a bullet jump of anywhere between (a minimum of) .050” up to .250” or more. … When selecting the cartridge overall length (COAL) we recommend starting with a minimum “jump” of .050” off of the lands. You can test different seating depths and find a “sweet spot” that your particular firearm prefers. We suggest working in at least .025” increments as follows seating the bullet deeper to allow a further jump.”

      Then they go on to explaining a test method that seemed similar to what Berger recommends.

      I didn’t find any data online from Cutting Edge or Warner Flatlines or Lehigh Defense about seating depth or bullet jump, at least not from them directly in my quick search. It is interesting. A topic of further research for sure!

      Thanks for sharing!
      Cal

      • Cal,
        I will share that every time I have run a load development for a copper solid like a Barnes TSX or TTSX, I have ended up with the bullets seated deep (aka, large jump).
        I have no idea why and some repeat work is required to go back and check if there was any correlation to pressure or SD events. I wasn’t always concerned back then and to be honest I was a little miffed that CA forced me to hunt in that Condor Zone with non-lead bullets. I was just happy to see good groups, and some wild pigs and coyotes were not. Great article with great references.

      • Thanks for sharing, Dino!

      • Seems crimping is totally ignored. I read years ago a CRIMPED bullet has a more consistent ignition BEFORE letting go of the bullet. Been squeeze crimping all my loads since & a definate improvement in accuracy w 10 fps spreads consistent regardless of all other factors combined.

      • Interesting theory. I’ve heard something similar about using a little more neck tension too. The theory one respected guy in the industry told me in conversation at SHOT Show this year was that if you had little neck tension, the chamber pressure didn’t have to build much to dislodge the bullet from the case and it would travel until it hit the rifling, but there wouldn’t be enough pressure built up to start pushing the bullet through the rifling yet. So it would travel out of the case, get lodged into the lands and stop for a brief moment as pressures continued to build in the chamber, and eventually when they got high enough it would start moving down the barrel. He thought if you used more neck tension it would give time for the pressures in the case to build a little higher so that when the bullet starts to move forward it won’t temporarily stop when it engages the rifling, but would have a more smooth and continuous movement through barrel.

        Now, I will say that is all theory and there wasn’t any science to back that up – at least that I’m aware of. I’m not saying it isn’t true, but it was just a off-the-cuff conversation from my perspective. But, your comments brought that conversation to mind, so I thought I’d least share it.

        There are only two scientific studies I’ve ever read related to neck tension. The first was from Dr. Harold Vaughn in Rifle Accuracy Facts. It was pretty short, so I’ll just include the full excerpt of what he said on the topic of neck tension:

        “The effect of neck tension on the seated bullet has been discussed in various magazines. None of these articles that I read seemed to have any real data so I decided to try to make some measurements. A load cell was made which measures the force required to seat a bullet in the bullet seating die. The load cell was an aluminum cylinder with two strain gages on it to measure the force. The force was indicated on a milliameter and the peak force required to seat the bullet was recorded. The peak force varied between 30 and 70 pounds. The test was run on a 6mm Remington case with 68 grain match bullets. Sixty rounds were tested and segregated into low ( 50) pounds seating force. The rounds were fired in 5 shot groups through an Oheler 35P chronograph in the Tunnel Range with a Heavy Varmint rifle. I could tell no difference at all between the high and low seating force in average muzzle velocity, extreme spread in velocity, or group size. Consequently, l am forced to conclude from the results of this limited test that bullet seating force has no effect on accuracy. However, this test was run on one cartridge and one gun, which is a very limited test and is not necessarily conclusive. It may be that a very light seating force (<10 pounds) may result in uneven bullet seating depth in the lands. This could result in greater dispersion. However, some successful Benchrest shooters use very light neck tension and do very well in competition."

        The other scientific study on neck tension was done by Bryan Litz and published in Modern Advancements for Long Range Shooting Volume II. He tested 3 different cartridges (223, 243, and 308) with 0.001″ of neck tension (relatively light) and 0.003″ of neck tension (relatively heavy). Bryan shares the full details in his book, but I’ll just share his conclusion here: “The 223 Remington saw its SD improve from 9 fps to 6 fps for the higher neck tension. The .243 Winchester saw an even more dramatic improvement in MV, going from 13 fps to 7 fps! The .308 Winchester which already had a respectably low SD of 7 fps saw no improvement for the higher neck tension.” So basically, Bryan found heavier neck tension was better in most cases, and at the very worse it was as good as light neck tension. If you find this interesting, I’d highly recommend getting Bryan’s book … there is even a good study in there on barrels from that PRB guy. 😉

        Probably more than you were wanting, but it is a great point – so I thought I’d just add a little more context for other guys who might be thinking the same thing. Seating depth, bullet jump, and neck tension are all closely related topics, and Bryan even discusses that in his research in the book.

        I appreciate you sharing your thoughts!
        Cal

  7. Jonathan Phillips

    A random aside and something that adds even *more* fun to the idle thoughts of a reloader: so what happens as the barrel breaks in? Do you chase the lands as they slowly wear? Do you allow the natural increase in free bore? How fast are they wearing? A small belief of mine is that if you can ensure bullet runout as low and as consistent as possible (and mark high points on the cartridges so you can chamber them in a consistent orientation) they are less likely to have measurable consistency variations due to increasing free bore…. But then again, I may be trying too hard lol

    Natutally, overbore cartridges are more likely to have to deal with this as their barrel life is measurably shorter and may necessitate measurement and adjustment every few hundred rounds, but these tiny variables slowly increasing with every shot kind of eats away at the consistency that we might spend hours working towards with our hand loads -_-

    • Jonathan … you couldn’t have led into my next post any better than that! Seriously! My next post will be focused on that exact subject, and I bet it has some surprising info in there for many of us. It certainly surprised me when I started diving into it.

      So in reply here, I’ll just say stay tuned. But I promise I will try to answer your questions in-depth in the very next post.

      Thanks,
      Cal

  8. Hi Cal
    Just spent two weeks shooting with Scott Satterlee in South Africa. He was out here running some training sessions and doing some hunting.
    He has some really interesting insights and ideas about bullet jump and seating depth. Definitely worth having a chat to him when you get feedback from the Pros.
    Looking forward to the rest of your posts on this subject!
    Kind Regards
    Grant

    • Hey, Grant. You are right. I have talked with Scott at length about this, and I’ll be including his perspective in this series of posts. Scott is pretty pumped that I’m publishing this. We’ve had multiple conversations about this, and I’ll include some of his data and details about what he is currently running. He’s a knowledgeable guy and clearly one of the best long range competitors in the world (finishing in the top 10 in the PRS and NRL rankings), so I thought it’d be good to add his voice to this conversation. You should definitely stay tuned for that, because you probably know where this is going. 😉

      Thanks,
      Cal

  9. Great article! I was curious to know how far off the lands do you load your 338 lapua and your 300 norma mag? Also have you been able to get low extreme spreads with your 300 Norma mag? Thank you!

    • Hey, Jay. Good questions. I’ll answer about whether I’ve been able to get low extreme spreads with my 300 Norma first, because it might be relevant to your other question about the jump I’m using. My initial response is “not really.” For an ELR gun, I’d like to have my standard deviation (SD) around 5 fps or less, ideally. I went back just now to look over my range data and over multiple 10 shot strings, my ES typically ranged from 27-35 fps and the standard deviation (SD) ranged from 8.7-11.5 fps. Honestly, I’ve struggled more getting a really consistent load with my 300 Norma Mag than any other cartridge I’ve done load development for. Since I started loading with a Prometheus powder scale, load development for most cartridges has been super-easy.

      Now the question of what my jump is on my 300 Norma, I actually just recently started using a new method to measure the distance to the lands which is super-precise and repeatable to within at least +/- 0.001″, and I just pulled my 300 Norma barrel last week to measure it and I was surprised by what I found. My previous measurement method was like probably a lot of other people, basically seating a bullet in a case and then chambering the round and repeatably adjusting the seating depth down very slightly until there was no longer any rifling marks on the bullet. It turns out, you are actually still seated into the lands slightly even when there aren’t any marks on the bullet, which is what I realized when I measured it using a more precise (but also more involved and time-consuming) method. On my 300 Norma, I thought I was jumping very slightly (around 0.005″), but it turns out I have been seated into the lands 0.010″. That actually could be part of the problem with my velocities being a little inconsistent, but that is just a theory at this point.

      On my 338 Lapua, I actually haven’t measured what the distance to the lands is using the more precise method yet. I’ll pull the barrel this afternoon and measure it and get back to you, because I have been wanting to do that anyway. I think I’m jumping the bullet pretty good, but can’t remember and couldn’t find it in my notes when I did a quick search … although I know I have my old measurements somewhere. I will say my SD’s on that rifle are stupid low. I have fired 10 shot strings that had SD’s of 3.2 fps, but they may range up to 5.6 fps. That’s the kind of consistency I like to see in an ELR rifle, and why I’ve been able to draw a smiley face on a target with my 338 Lapua at 1400 yards. That is the rifle and ammo I have the most confidence in of any that I own. So I’ll get back to you on the 338 Lapua bullet jump. I’m actually anxious to know myself, knowing that the velocities have been so consistent. I will say I haven’t been managing it much (i.e. not adjusting seating depth very often to “chase the lands”), so I might be surprised where it is at. The performance definitely hasn’t degraded, because I won an ELRSO competition with it last time I had it out.

      Great questions! I’ll try to get back to you on the 338 Lapua bullet jump.

      Thanks,
      Cal

      • Hey, Jay. I took my barrel off my 338 Lapua today and very carefully measured the distance to the lands using a technique that I’ll share in the next post. The old way that I tried to figure out the distance to the lands was not precise or repeatable, although I thought it was until recently. It is what a lot of other shooters probably do, which is simply closing the bolt on a loaded round and seating the bullet incrementally deeper until there were no longer rifling marks on the bullet. It turns out that is not precise or repeatable.

        So it turned out, after using the more precise and repeatable method of measuring, my distance to the lands was much shorter than I thought it was. That means I’ve been seating into the lands a considerable amount. It wasn’t enough to leave marks on the bullet, but that doesn’t mean it wasn’t seated into the lands … it just means there weren’t marks on the bullet. Turns out those are two different things and there is a large difference. Kind of surprising, honestly … but that’s why I prefer to measure things instead of just guessing.

        I will say that I bet most guys aren’t measuring the distance to the lands in a way that is reliable. There are only two ways I’ve come across that seem precise and repeatable, and one requires you to take the barrel off and the other requires you to disassemble your bolt (including the extractor and also the ejector, if it is one of the plunger styles that is in the bolt face). So both are a bit of a hassle, but I’m not sure there is another way to measure it that is repeatable even within +/- 0.005″ and maybe not even within +/- 0.010″. The method I’ll talk about in the next post seems to be repeatable within +/- 0.001″.

        That’s all probably more than you wanted to know, but it’s my long answer to say that my 338 Lapua ammo has been seated into the lands. 😉

        Thanks,
        Cal

      • Thank you for tge reply! I have allot of time into the 300 norma mag. I had 1/4 inch groups with H1000 but my extreme spreads were not good. I finally got my hands on some n570. If you get a chance try some of that and see if your numbers get better. I have a mile range at my house so I shoot allot at 1 mile. My target is only 24 inches so i’m sure you can do the math and figure out that I need low extreme spreads to consistently hit the target at that distance. Although I am having better success with n570, I read your post on how accurate your 338 lapua is and how your extreme spreads are so low so i’m going to try one myself. Do you usestainless steel media to clean your brass or just corncob media? On the subject of finding your lands, I do the method that involves taking my bolt apart. It’s a very accurate way to measure it. Thank you for the reply!

      • Thanks for the tip, Jay. I appreciate that. I’m a corn cob guy. And taking your bolt apart is a great method. I actually just created an instruction page that details the method I use. You can check it out here if you’re interested, but I’m not going to say it’s more accurate than the method where you disassemble the bolt. In fact, I mention that method at the bottom of the page, just so guys are aware of that option … because it’s just as precise and repeatable, in my opinion.

        https://precisionrifleblog.com/how-to-measure-the-distance-to-the-lands-on-your-rifle-barrel/

        Thanks,
        Cal

  10. Cal,
    I live in California, where the CDFW, in their infinite wisdom has mandated non-lead projectiles in every aspect of hunting within the State. I am a reloader and have always loaded my rounds touching the lands for the best accuracy. When I begin reloading with non-lead, I selected Barnes copper. After many practice rounds with various bullets, weights and powders, I still could not get my rifle to produce a decent pattern with the non-lead. I called the Barnes factory representative and was told that Barnes bullets do NOT like to be up against the lands and shoot best when they jump. Desperate for anything that would work, I tried his suggestion. Reducing the COAL and having the Barnes bullet jump to the lands has definitely improved the accuracy in my firearm and given me a consistent MOA I can live with. Go figure!!

    • Hey, Larry. Thanks for sharing your experience. Another reader left some comments to a similar effect, noting that the conventional wisdom all these resources are proving may not be applicable to monolithic/solid bullets, like Barnes, Cutting Edge, Flatline, Lehigh Defense, Berger’s new line of copper solids, etc. However, I didn’t notice until the comments today that none of the stack of books I own actually ever draw that distinction. I did find a similar recommendation from Barnes on their website and quoted that in my response to the other comment someone left about solids, but it lines up with exactly what you said. It certainly makes me wonder how they are different and what is the underlying reason for the difference. Maybe the lead core responds differently or is more malleable than a solid when it engages the rifling? I’m just pulling that out of my butt, but it’s definitely something that’s got me thinking! I guess if it works, we should just use it … but something in me isn’t quite satisfied until I know WHY it works. 😉 I guess that might be another research idea I’ll file away on a shelf.

      Thanks for sharing,
      Cal

  11. Very interesting reading coming I can feel it! I’m probably the odd guy out here. For years I messed around finding the land then 0.005 at a time…… then I read Bergers idea on jump now I find the lands 0.030 at a time done! If 0.09 and 0.12 are good I load 0.09 and forget about it. Both my 115 VLD and 115 DTAC like 0.120 who would have thought? I found a lot bigger difference going with the bigger incerments. Mind you I’m not after benchrest accuracy but good solid consistent loads. I’m looking forward to what you have all found. Regards John

    • Hey, John. Thanks for sharing. I will say that while it seems like all of these resources seem to encourage getting close to the lands or even into them, you’re not the first person I’ve heard say they had good luck with longer bullet jump. It definitely seems more rare though, compared to jumping 0.020” or less. I’d definitely say you should stay tuned. There are some interesting trends in some of the new, primary research I’m about to publish.

      Thanks,
      Cal

  12. Have joined the fun for about a year now and follow ALL of your posts with great enthusium. YEARS ago I bought and read a really good book on bench rest shooting. Unfortunately, I have misplaced the book and been unable to find it online (don’t even remember the name of the book). I do remember them recommending “on the lands” for best accuracy. I also remember the discussion on the 6mmPPC being the hands down favorite cartridge. It always intrigued me how that cartridge never made it into the mainstream. I was elated when Browning&Winchester came out with the WSM line of cartridges as I thought it was a step in the direction of the 6mmPPC design efficiency and immediately jumped on that bandwagon and invested in the Browning Eclipse M1000 in 300WSM. I love that gun and it is that cartridge that got me into reloading because the rest of the world did not share my interest for the WSM and cartridges became hard to find and stupid expensive. About that same time I came across your blog and and followed with great interest in the new PR fad and the new 6.5 Creedmore, and that evolve into the 6mmPRC and the half dozen or so other cartridges. Jumping on the bandwagon (just for fun) I decided to build a rifle. There is no substitute for a good gunsmith but for the average Joe the wait to get things done can be unbearable. My guess is a lot of gunsmiths got into the business because they got tired of the wait. So I built on a Savage target action and a couple of Bartlien barrels (300WSM & 6.5 CM). Being a target action I am not limited to a magazine length so I can run 147gr and 150gr 6.5mm match bullets to desired seating depths and love that flexibility. Not doing PR match stuff so speed is no issue. What is frustrating is I am now loading for my son’s Ruger Precision rifle and being mag fed I am at best around 97 thou off the lands. I find that does not fit my Idea of a precision rifle. Seriously, how hard would it be for manufacturers to increase the mag length to accommodate the new higher BC offerings for all of the bullet makers. Just between you and me I am getting 3,000 fps on 147gr and 150gr bullets with 47.6 gr RL26 and a 28″ BBL and running 15thou off the lands. Seriously don’t know how you find the time to do all you do…and stay married but I am glad you do!

    • Hey, Kenny. I can appreciate your excitement! I totally agree about the magazine length issue. I just wish everyone would move to longer magazines. The truth is over the past 20 years people have migrated to heavy-for-caliber bullets (at least in the long range world), and those are typically longer and have issues fitting in magazines designed before that was a thing.

      Kenny, I think you’ll find this series of posts interesting. I think you might appreciate some of the ideas we’ll explore. Stay tuned!

      Thanks,
      Cal

  13. thanks for sharing , and again ! you always post great articles .
    Before reading this article, I almost never thought about this problem, i mean the relationship between center and coal. This is an enlightening point.

    best wishes

  14. Since I am brand new to this game & thoroughly confused by “jump”, I measured the headspace/ COAL on my Howa 1500 6.5C (2.874) with a Hornady Comparator> And measured COAL on various Factory Match cartridges. Huge differences. An ELD MAtch 140gr comes in at 2.656. And yet I get “good” results with the ELD. What am I doing wrong ?? Not sure what length COAL to make my loads.

    • Well, if you are satisfied with the results you are getting … I’d say don’t fix happy. Often times it comes down to what someone’s goals are for precision. If you are using factory ammo and not reloading, you can ignore this post. This is really only for the guys who are customizing a round they are handloading to be ideal in their chamber. If you’re using factory ammo, I’d just keep shooting it! I am going to mention a few things in this series that might potentially be a way a gunsmith could build a rifle that is more optimized for a particular kind of factory ammo. But bottom line is if you are using factory ammo in a factory rifle and getting good results … you should ignore this stuff and just go shoot. Sometimes we can overly complicate this, which is especially true the deeper down the rabbit hole you go.

      If you really want to understand this stuff better, and make sure you’re thinking about it the right way, I’d highly recommend buying Top-Grade Ammo. It is a good overview with lots of photos and even has equipment recommendations and stuff for those getting into reloading. I tried to cover this in a way that I didn’t lose people, but unfortunately I probably can’t represent all this in a comprehensive way like a book like that would.

      Thanks,
      Cal

  15. Sorry Cal: I didn’t make it clear. I DO reload. Was just using factory ammo till I got started. Basically trying to figure out what the ideal COAL should be for my rifle. So should I load to the length I got off my rifle or that of the factory ammo..A 0.218″ difference. Will get the book you recommend. Thks for yr help. Rgds. Ghalib

  16. Thks Cal: That was super quick & much appreciated. Just ordered the bk!

    • I’ve read a stack of them, obviously! 😉 I find that one to be a great reference. It even comes in a spiral-bound format that makes it easy to just open up and reference on your loading bench as you’re working. I bet you like it!

      Thanks,
      Cal

  17. Hi Cal,
    New to the PRS and I am shooting a Seekins SP-10 semi-auto in 6.5 creedmore. I was wondering if the optimal
    “jump” is in that same range of touching to .020″ to maximize accuracy. I am limited by my mag COAL of 2.800″ my barrel had .100 jump at 1000 rounds and is now up to .123″
    I will be changing barrel soon to an X-Caliber and will see what I get.
    Are semi’s different.

    • Great question, John. I can’t say that I’m an expert in semi-autos, but I’d think it’d be similar … but I don’t know that. I personally would be hesitant to seat into the lands or even less than 0.020” jump to the lands with an AR. If I were you, I might reach out to Seekins and see what their recommendation is.

      If someone else has experience with seating depth in large frame AR’s, please chime in here in the comments!

      Sorry I couldn’t be more help,
      Cal

  18. Cal,
    I’m sending this as a personal note and entirely understand that you may not wish to publish shameless self promotion or be seen as a sponsored infomercial.
    The information regarding monolithic projectiles is provided as an information source for cross referencing only. You did say you looked at the Barnes, Lehigh and Cutting Edge websites …
    Have a look at our website, outeredgeprojectiles.com.au
    Some of the information is a little outdated and needs to be reviewed, but provided in good faith.
    You won’t find any scientific data collection posts there, but the principles explained are the result of a great deal of research and testing (how much scientific data should be posted on a product website is an eternally perplexing issue!)
    Being a monolithic projectile manufacturer, we are constantly making the case for the differences in loading techniques to enable our customers to get the best results for their efforts. Much of our research is universally (to monolithics anyway) applicable, not proprietary.
    The analogy of confusing petrol with diesel is a good one; the differences really are that stark.
    Whilst our research, like all research, is never complete and we don’t have all the answers, we are starting to get a pretty good handle on how and why things are different and what does, and doesn’t make them work.
    For example, another area for research is the influence of barrel land configuration.
    Copper bullets don’t like polygonal or canted lands, but generally work exceptionally well with standard and ratchet land configurations.
    But that’s a story for another day
    Cheers
    Steve H

    • Wow, Stephen. That doesn’t feel like a shameless plug at all. I appreciate you sharing a link to your findings. We’re all just trying to figure this stuff out, right?! Of course a bullet manufacturer wants their product to perform at its best, so they typically do have recommendations on how to make it so. It did surprise me to not find more on those other websites honestly. I appreciate you sharing the info you have.

      Thanks,
      Cal