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7mm Rem Mag Load Development Part 4: 5 Shot Groups

I’ve already done quite a bit up to this point in my load development.  At this point I know I want to try to find an accurate load for Berger’s 168gr VLD over Hodgdon’s Retumbo powder and I’m now zeroed in on a very specific range of powder weights that seem to be very tolerant of slight pressure variances.  You can see the previous posts for how I got here.

My next step is to test 5 shot groups in very granular powder increments.

Jump to another step:

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. His engineering background, unique data-driven approach, and ability to present technical and complex information in a unbiased and straight-forward fashion has quickly caught the attention of the industry. For more info on Cal, check out PrecisionRifleBlog.com/About.

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  1. I would be careful using the Retumbo powder, for it is used for ultra mags. With the slow burning difference between Retumbo and H1000 you might have an issue with too much pressue build up thus causing major issues. I Would get in contact with Hodgdens powder first before I try the Retumbo powder.

    H1000 is specifically made for 7mm mag rifles, and still is a slow burning powder.
    good luck!

    • Thanks for the tip, it’s a great reminder. You should certainly always be careful when handloading with any powder, and build up loads slowly, constantly checking for any signs of pressure along the way.

      Hodgdon does list Retumbo as an appropriate powder for 7mm Rem Mag in their reloading data. It’s also referenced as a powder choice for 7 Rem Mag in Berger Bullet’s reloading manual, and manuals published by Hornady, Sierra, and Barnes. I have personally shot 1400 rounds of Retumbo powder out of my 7mm Rem Mag with no issue so far. The gunsmith who built my rifle also found Retumbo provides more consistent velocities out of 7mm Rem Mags when using heavier bullets, but I know other accomplished shooters who use H1000. They’re both viable options. Thanks again for the comments.

  2. The one thing that I have found is that the temperature and wind makes a big difference in the speed of my bullets using the same charge weight.

    • Temperature and wind definitely influence where the bullet hits. Temp & wind both influence external ballistics (i.e. bullet flight), but only temperature affects internal ballistics (what determines muzzle velocity). Without getting too nerdy, is a breakdown of the ballistics life-cycle of a bullet (at least the major parts).

      Ballistics of a Bullet - Internal Ballistics, External Ballistics, Terminal Ballistics

      Since wind can only effect external ballistics, it actually can’t change your muzzle velocity. It definitely changes the flight of the bullet … just not the initial speed the bullet exits the barrel. Temperature on the other hand does impact both internal and external ballistics, which means it CAN change your muzzle velocity. Some powders are better at minimizing this effect than others, but no powder is immune to temperature changes. That is why I exclusively use Hodgdon Extreme Series powders. These powders all have a coating that makes them less temperature sensitive. This means the muzzle velocity will vary less. In fact, Hodgdon has published some test data that shows how different powders perform from 0 to 125 degrees. I take it with a grain of salt, since they’re obviously biased … but my own experience closely matches these results.

      Hodgdon Extreme Series Temperature Variation from 0 to 125 degrees

      Of the top 50 shooters in the Precision Rifle Series, 96% use Hodgdon Extreme Series powder. That is quite a statement. There are more than a couple believers in this series of powders.

      To me, its just so frustrating for a bullet to shoot completely different when its 50 degrees at 8am in the morning than it does when its 90 degrees in the afternoon. I’ve seen guys literally change dope cards multiple times during the same competition because of the temperature variation in their powder. That’s why I won’t even try to do load development on anything but the Hodgdon Extreme Series powders. If one of my rifles won’t shoot one of them well, I’d rather sell the rifle than put up with that kind of headache.

      Disclaimer: Hodgdon is not a partner or sponsor of my website, and I’m in no way affiliated with them. I’ve been buying their powders at full retail price, just like everyone else. So this is an honest opinion, not a paid commercial.

  3. I’ve had good results in three rifles with a load very similar to Cal’s

    Federal 210M primers, Norma brass, 72.0gr Hodgdon Retumbo, Berger 168 VLD, COAL 3.380″ (0.086″ off lands).

    Repeatably shoots 0.3″ 3-shot groups into a 175yd target (when I’ve not had coffee that morning).
    Only 13¼ MOA drop to 800yd target.

    Very confidence inspiring. I know the rifle and ammo will do their part, if the wingnut behind the trigger is doing his job. No worries about my equipment or loads, just have to get calm and shoot straight.

    Only 28 MOA drop to 1250yd target. Coriolis drop, Eötvös Effect, and spin drift at 1250yd is ¼MOA down (shooting west) and 1MOA right to that target. That is a flat shooting load, when esoteric “voodoo math” effects like Coriolis drop, Eötvös Effect, and spin drift are a noticeable adjustment to your point of aim yet you can still shoot with holdover in your reticle without dialing the adjustment into your turrets.

    Alternate loads that work well;

    162 A-Max and 70.0gr H1000. (Norma brass, Fed 210M).

    Berger 180 Hybrid, 72.0gr Retumbo, COAL 3.530″ (0.020″ off lands), Fed 210M, Norma brass

    (Standard disclaimer: These loads are above listed safe values. They were carefully worked up to, starting from minimum published loads, over the course of years of reloading, with a few specific rifles.)

  4. Cal…I may have missed it but would you please recap the method used to determine bullet seating depth? I’ve never had anything but frustration with the Berger VLD bullets. My rifle is a custom but it has a standard SAAMI chamber. If this is ground previously covered I apologize.

    • Cal, I am familiar with the published method that Berger came out with years ago (fire test groups at -.005, -.050, -.100 etc). Just curious as to whether you used this step in your load development. It would seem to me that the seating depth is critical to accuracy.

    • I typically start by using a Hornady OAL Gauge. There is a video below that shows how it works.

      [youtube http://youtu.be/WCPgKNp8i7o%5D

      After that, I usually seat a bullet in a case at the depth I think it should be and try to chamber it in the rifle. If the bolt is too tight, I seat it deeper. If it chambers, I’ll eject the round and make sure the bullet came out and has marks on it. I typically prefer to get the bullet to “kiss” the lands, which to me means that there are marks on the bullet … but they aren’t very long. They may be roughly 1/2 as long as they are wide. Since I’m a practical/tactical guy, I NEVER want the bullet the to become stuck in the lands. Benchrest guys do that a lot, because thats where they find the best accuracy. They typically have to send a round down range after they chamber it. But in matches or hunting scenarios, that is a terrible option. I typically chase the lands as the barrel starts to erode, so that I’m always touching them … but not jammed into them.

      Here is a quote I keep in mind when thinking about seating depth. It’s from The Secrets of the Houston Warehouse. You might check it out if you haven’t already. Awesome read!

      …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.

  5. For overall length gauges, I use a black magic marker to color the gauging bullet. When the bullet touches the lands, it shows up much better as bright scratches on a blackened bullet.

  6. I’m reloading for a parker hale 7mm rem mag. I used the hornady o.a.l gauge to find my bullet seating depth. After many attempts I came up with 2.957 for the ogive o.a.l. That puts me way over the max recommended c.o.a.l. I am using berger 168 vld bullets. The bullet is only seated by about .15. Just wondering if there is something different about parker hales or if I am missing something somewhere. The chamber looks fine. It shoots decent groupings when the bullet is seated at the max recommended c.o.a.l. But i’m worried about chamber erosion if I keep it like that. Is the bullet seated far enough in so I wont have problems or do I need to bump it in farther? Or is there something different about my gun or that I’m doing wrong?

    • Hey, Kurt. I’m not familiar with the Parker Hale 7mm Rem Mag, but I’d expect that the chamber reamer is slightly different dimensions than what most custom gunsmiths use for a 7mm Rem Mag designed to shoot VLD bullets. One thing about the 7mm Rem Mag is since it is an “older” cartridge (at least relative to many of the popular rounds on the market), there are a ton of variations of chamber dimensions out there. The VLD bullets are an extreme shape (very long nose for “Very Low Drag”), which means they may work better in some chambers than others. You may have a chamber that isn’t ideal for VLD bullets. Some gunsmiths “short” the chamber on rifles designed for VLD bullets, so that they don’t have to be seated out as far to touch the lands.

      Here is a link to the chamber print for my 7mm Rem Mag compared to the SAAMI minimum dimension chamber print. It will help illustrate the kind of variation you can expect in 7mm Rem Mag chambers.
      7mm Rem Mag Chamber Print

      One thing about VLD bullets is they are typically very sensitive to seating depth. If you can tune the seating depth so the bullet is next to the lands or even touching the lands, it can have a dramatic impact on precision. I’d suggest you try Berger Hybrid bullets. They have the same high-BC, but are much less sensitive to seating depth. You can usually “jump” those bullets (i.e. they aren’t close to the lands), without much consequence to group size (if any).

      I’d be a little concerned with bullet runout with it being seated so far out and not being all the way within the neck. That just means how aligned the bullet is with the bore. It would be easier for it to be off-center one way or the other and that can affect accuracy, and even chamber pressure and muzzle velocity to some extent.

      If it were me, I’d probably switch to a Hybrid bullet or a bullet with a tangent ogive design. The VLDs have a secant ogive design, which you probably want to avoid if you don’t have fine control of seating depth. Here is an article that explains the difference of those in more depth: Tangent, Secant, Hybrid Ogive Bullets: Bryan Litz Explains Characteristics of Different Bullet Ogive Designs

      Hope this helps!

      • I will look into the hybrids. Thanks much!

      • When switching to the hybrid bullet should I still seat the bullet as close to the lands as possible? If so are there guidelines for bullet to neck ratio as far as how far out I can bump it? Thanks for the info! Always fun to get an education!

      • I’d push the bullet out at far as you could, but still keep the bearing surface in the full length of the neck. That can help with concentricity and more consistent neck tension. I typically prefer to minimize jump, but I haven’t noticed any accuracy loss with the Hybrids when I’m not able to do that. In fact, the throat on my 6XC has eroded to the point where I can’t touch the lands if I want to still fit a loaded round in a magazine … so I’m jumping the bullets. I’ve actually fired my best groups with that rifle doing that (0.11 MOA). Seating depth on those hybrid bullets just doesn’t seem to be as critical as other designs.