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The first step in load development for my new custom 7mm Rem Mag started with gathering the real-world velocities I could expect out of three quality long range bullets I was considering. I then used those velocities to compare the ballistic performance between those three bullets, as well felt recoil during the test rounds. I eventually decided to pursure further load development for Berger’s 168gr VLD bullet over Hodgdon Retumbo powder because it struck the right balance for me between the competing characteristics (recoil, barrel wear, flat trajectory, low wind drift, ideal energy for medium sized game, etc). For more details on this first step, see my post about it.
After choosing the bullet, I used Hornady’s OAL gauge to determine the approximate bullet seating depth that would be just off the lands (.005″ – 0.010″ off the lands). For my chamber, that was 2.770″ from the base of the loaded round to the ogive of the bullet. Note: You should always measure cartridge overall length (COAL) to the ogive of the bullet, not the tip of the bullet. Since I’m shooting a Berger VLD bullet (highly sensitive to seating depth), I will come back and fine-tune seating depth again after I settle into a powder weight … but for now, I just want it to be very close to the rifling.
My next step was to use Creighton Audette’s Ladder Test to identify a range of powder weight that show little sensitivity to minor changes in charge weight and/or pressure. Theoretically a range like that would allow a bullet to group even if a particular component varied slightly (e.g. primer was slightly hotter, neck tension wasn’t identical, there was .05 to 0.1 more or less powder in it, there was more/less bearing surfuce on the bullet, etc).
I’m purposely trying to stay in the mid-range of powder charges for the 168gr VLD for reduced recoil and barrel wear. You could definitely load the 7mm Rem Mag up or down more than what I’m showing here … but I felt like this range of powder charges was the right balance for me, because the ballistic advantage of loading it up a few more grains really isn’t that significant.
Here are the results of my ladder test. You should disregard horizontal dispertion. It was due to slight wind drift (targets were placed at 200 yards), because I used the same point of aim for each shot without holding for wind. With the ladder test, the things you want to focus on are vertical dispertion & muzzle velocities. After you settle in on a round, you can fine-tune grouping and figure out what adjustments you need to make for wind drift.
Based on these results, its clear there might be a sweet spot somewhere between 69.6 to 70.0 gr of Retumbo. I actually had a match come up before I could do further load development, and so I just loaded rounds at 69.8gr of powder based on these results. Although I hadn’t ever shot that round past 200 yards and only had “theoretical dope” past that … I made it 80% of the way through that match before my first miss, and ended up placing 2nd. The dope was good out to about 600, but beyond that I had a few misses. I also later fired a 0.188″ group with my first 3 shot group of that load.
Despite these stellar results, the ladder test isn’t the last step to load development. Unfortunately it is very dependent on single shots, so results could be easily skewed by one outlier that had a hot primer, bad chronograph reading, or more/less neck tension or bullet runout. Having said that, it’s still sometimes suprising how quickly the ladder test will help you zoom into an accurate load.
Jump to another step:
- Part 1: Bullet Selection & Real-World Velocities
- Part 2: Audette’s Ladder Test
- Part 3: Optimal Charge Weight
- Part 4: 5 Shot Groups
According to the reload data I am able to find on this particular load, the recommendation is between 65.5 and 71.1 grains of powder. Can you tell me how you came to the conclusion to limit your initial loads to between 69.0 and 70.8 grains? I am having trouble finding powder and plan on using IMR4831 as I have a lot of it available. The range recommended for this powder is between 53.5 and 59.4 grains. I would like to limit my search rather than load bullets in .2 grain increments over this entire span. Do you have any suggestions. I plan on using CCI 250 primers (based on availability as well)
That is a great question, and caused me to do a little digging because honestly I can’t remember off the top of my head. I don’t believe the Berger Reloading Manual had been published when I originally did this. I remember looking at load data from several other manuals, and they seemed to be all over the map. Here is what I found:
Sierra Reloading Manual
168gr Bullet over Retumbo, Start: 69.0gr, Max 71.1gr
Hodgdon Reloading Data Center
162gr bullet over Retumbo, Start: 69.0gr, Max 73.5gr (compressed)
170gr bullet over Retumbo, Start: 71.0gr, Max 75.0gr (compressed)
Hornady Reloading Manual
162gr Bullet over Retumbo, Start: 62.9gr, Max 70.1gr
175gr Bullet over Retumbo, Start: 59.7gr, Max 65.4gr
Since Sierra and Hodgdon both didn’t have a starting weight under 69.0 grains, that is what I set my start to. Then Sierra had a max of 71.1 grains, but Hornady had an even lower weight for their max load. So I set my max load to a somewhat conservative 70.8 grains.
Ultimately, I’m not the kind of person who loads really hot to get a few more FPS out of my rifle. Hot loads can dramatically increase barrel wear and decrease brass life … not to mention be dangerous. So if you find yourself trying to eke out a little more velocity, you might be better served by picking a different cartridge that is more suited for the muzzle velocity you are targeting.
If I were doing it again, I’d probably just pay attention to what Berger says on the matter. I have a lot of respect for those guys, and they are obviously testing against the exact bullet I’m using … a 168gr Berger VLD. Here is what their manual says:
Berger Reloading Manual (Published AFTER I did this load development)
168gr Bullet over Retumbo, Start: 65.5gr, Max 71.2gr
Great question! Sorry it took me a while to dig up the answer for you. It caused me to go back in time and try to figure out what was going on in my own head … quite an adventure!
i was new to reloading and became interested when I had a custom 7 mm rm built ( interarms action set trigger 1.8 lbs Mcmlllian stock 27″ bartlien barrel after reading about your build I learned an awful lot about reloading from your post. I’m just starting load development using 168 accubond lr bullets. Nosler brass fed 215 primers and starting with 67.1 gr h1000. Loaded 3 gr increments .035 off the lands . I load 3 of each grain end up with around 48 rounds and after a day at the range can be pretty sure I’ve the best load. Ive 3 questions. Is there a better/ faster way to to get to the best load. For that combo? How to know you in the right zone on seating depth if I change the depth do I need to start from scratch on load development. Last but not least when do we get part 4 5 shot development ………. You can’t leave us hanging. Thanks for your article. You are highly talented
Hey, Daniel. Glad you found this stuff helpful. This is the best approach to load development I’ve found. And on the seating depth, I usually find the best accuracy either really, really close to the lands or kissing the lands. Because I’m a tactical/practical guy, and not a benchrest shooter so I never jam the bullet into the lands. That can leave the bullet stuff in the chamber if you need to extract the loaded round without sending it. When I do my load development, I typically seat the bullet out incrementally until I can see tiny marks from the rifling all the way around the bullet. I always thoroughly check to see if it would ever get stuck in the lands, and if it doesn’t … that’s my spot. That’s what I call “kissing the lands.” I continue to check the seating depth about every 100-300 rounds, and will seat the bullet out further as the throat erodes. Ideally, I’d like it to always be kissing the lands or just off the lands.
If you have more questions about this kind of stuff, you should check The Secrets of the Houston Warehouse article. It is one of the best articles I’ve ever read on the subject of handloading and world-class precision. Here’s one takeaway from that article that shaped my approach to this:
And sorry I trailed off on Part 4. The 5 shot development didn’t change a thing, and I got busy. I should go back and remove that so it’s less confusing. My bad.
Hope this helps!
Cal
Following Mr. Dan Newberry and your steps on this load development, I came up with real close results to your test!!!
7 Rem Mag/Win brass/168 SMK/Retumbo load. CBTO 2.790 kissing lands COAL 3.357 kissing lands Fire-form win brass(hsm factory ammo)
Headspace set at left at 2.111″
Trim 2.490″
Primer fed match 215
Retumbo powder
168gr 7mm .284″ SMK bullet
OCW was found at 69.6 grains of Retumbo At 100 yards
3 shots 69.3, .411″ moa,
3 shots 69.6, .590″ moa,
3 shots 69.9, .500″ moa,
They all show real similar POI
However I came across at my local shop with a box of Nosler 7rem mag brass and I would like to know how much powder do I have to reduce or add to my current OCW.
Here is some data on my new nosler brass and current fire form win brass
New unfire Nosler Brass
Head space: 2.100″
Trim length: 2.490″
Internal H2O capacity: 85.25
Empty brass weight: 218.4
Fire-form Win Brass
Head space 2.111″
Trim length 2.490″
Internal H2O capacity: 85.90
Empty brass weight: 235.35
THANKS
That’s pretty amazing. At this point, I’ve heard a few people say they ended up with very similar results. I do think this is at least some anecdotal support for Dan Newberry’s loading approach, and the fact that some loads shoot well across multiple different rifle platforms.
Thanks for sharing!
Cal
When developing a load. From what I have read first audettes ladder test. Then narrow in on using OCW in .3 gr steps for magnum then further test say higher precision charges. When should I introduce testing for optimal bullet jump? Does the bullet jump have impact on that above or does bullet jump just further refine the accuracy beyond audettes and OCW methodology? Assume I would do the above with say .020 jump? 300prc 225 ELD-M
Hey, Peter. I’ve got to be honest … I actually have changed my load development process quite a bit over the years. I don’t start with the ladder test, at least like it is laid out below. It would probably take a multi-part series of articles to lay it all out and explain the why behind all of it, but I have simplified my process dramatically. I’ll try to outline my process, and hope it’s helpful.
Keep in mind that my application is primarily PRS matches (I’m classified as a Pro shooter, so I’m very competitive at that) or hunting. Both of those are in field conditions, and not from a bench. My load development process would likely be very different if I was Benchrest or F-class, but that isn’t my application – or the application of most reloaders. The fact that you are shooting a 300 PRC leads me to believe you might be doing ELR shooting or hunting. I’ve placed in the top 5 at national-level ELR matches, and this is the same load development process I now use in that application as well.
1) I basically start with a bullet and speed in mind that I want to run. Then I pick a cartridge that can easily launch that bullet at that speed without being close to max pressure. I prefer cartridges that Alpha or Lapua makes factory brass for, but I now use ADG brass for my 7mm Rem Mag. ADG brass is good, but you’ll never get as consistent muzzle velocities as you can with Alpha or Lapua brass.
2) Then I buy enough components for the full life of a barrel. If I think a barrel in that cartridge will likely have around 1200 rounds of accurate barrel life, then I make sure I have 1200 of those bullets, 1200 of the primers that I want to run, and for 1200 rounds, I might buy 200 pieces of brass. When I have all that stuff in my hands, I place an order with a gunsmith for a barrel chambered in that cartridge.
3) When I get the barrel, I load up 100-150 rounds that is a mild load with a really long bullet jump. I shoot all of that ammo before I start any serious load development. I want to get the barrel broken in, and as you do that your velocity will change quite a bit (sometimes by more than 100 fps) from what it was the first 20 rounds down the tube. Then I clean the barrel really good, and then might foul the bore with 10 rounds or so before starting load development.
4) Then I’ll load 1 round in 0.5 grain increments and fire those simply to record the muzzle velocities. That part is similar to the ladder test, but I’m not “looking for flat spots” like Audette was. The problem is the sample size. I’ve tried this myself and “flat spots” on a ladder test aren’t repeatable. If you do a ladder test and find a flat spot, I challenge you to repeat that same test 5 times on different days and see if the “flat spot” is in the same place every time. If there is real science behind that method, it would be repeatable. But I already know what you’ll find, because I’ve done that test myself a few times. That’s why I don’t look for “flat spots” any more.
5) After I have the muzzle velocities for different charges, I pick the one that gets me closest to what I was hoping my velocity would be before I even picked the cartridge. Then I load up 20 rounds for 3 or 4 different jumps, typically something like 0.050″, 0.075″, 0.100″, and 0.125″. I realize that is a lot longer jump than conventional wisdom suggests, but here is a very in-depth bullet jump article that is based on the largest research project ever conducted on bullet jump and it explains why I landed at testing those jumps. I’ll fire four 5-shot groups with each, and determine the mean radius for each jump. Then I load up hundreds of rounds of that, and shoot it. I usually start with 0.100″ and if my average over the four 5-shot groups is under 0.4 MOA … I typically won’t even try the other bullet jumps. I will just load up 300-400 rounds of that load and go shoot. It does fit my experience that some bullets are very sensitive to seating depth, and I know a few veteran reloaders who believe that seating depth is more correlated to group size than powder charge weight.
If you are consistently getting 3/8″ precision or better at 100 yards, then I feel like any minor tinkering with loads to try to get it to 1/4″ is trivial in my applications. For my application, it doesn’t help me hit more targets, so its not helpful. I also am very skeptical of whether most people’s improvements in a load would actually be repeatable in larger sample sizes. I believe most reloaders think they see patterns in group size, but their sample sizes are so small that it is actually meaningless noise that is exactly the kind you would expect to see in small samples. (Lots more on that in this article: Precision & Group Size – Statistics for Shooters)
I might check the groups and load once or twice over the life of the barrel, but in my experience – if you are using high quality components (bullet and brass specifically) and have a high quality custom barrel … you shouldn’t have to change your load much (if any) for that kind of precision. You also shouldn’t need an extensive load development process to get under 0.5 MOA with a custom rifle using match-grade bullets. If you do, then it’s likely a problem with your barrel or the lot of bullets you have.
I really started changing my mind about how critical load development was with a series of articles I wrote called “How Much Does It Matter?” It takes a very objective, science-based approach to putting in context how much group size, muzzle velocity variation, and other factors have on hit probability at long range. I’d HIGHLY recommend you read some of those artilces. I bet you’d find them very helpful: How Much Does Group Size Matter?.
I know that was long-winded, but you are asking great questions and I wanted to try to be as helpful as I could be. Like I said, it would take a whole series of posts to unpack everything that went through my brain when reading your question and my rationale behind my current process, but I’ll also say that I’m friends with many other pro shooters in the PRS and I’d bet the simple process I just outlined is more of the norm in that group than the exception. So I don’t feel like I’m an outlier, and I also feel like my results are not inferior to what any other pro shooter is producing. So it’s not that I’m lazy. Clearly, I’m a detailed guy who is very driven – but I’ve just learned through more than a decade of experience long range that a lot of the conventional load development methods aren’t necessarily helping you shrink your groups, find the best load, or get more rounds on target.
Thanks,
Cal