Developing a Load for Competition Shooting, Part 2
In Part 1, we outlined the six steps in developing a good competition load:
Those steps were very easy with our 6BR, as that rifle had a “history” of preferring Berger bullets. Varget powder was virtually the standard and the load range was fairly well established. With the arrival of Susannah’s new Savage M12 F-Class rifle, in 6.5x284, things became more complicated.
Bullets: We had no idea as to what bullet would work best in this gun. The 142 grain Sierra Match Kings, 139 grain Lapua Scenars and 140 grain Berger VLDs are used by competition shooters around the world, but which one would work best in our gun? Since we already had a good supply of 139 grain Lapua Scenars we decided to try them first. If the results are not acceptable, we will buy a batch of Bergers or Sierras and start testing all over again. Although our choice of bullets was not scientific, you have to try what you already have before buying something new.
Brass: This choice was easy. We use only Lapua brass for all of our competition shooting. If there was a better brass, we would buy it. Lapua is the choice of most champion shooters, so we picked up seven boxes of new 6.5x284 brass.
Powder: Hodgdon’s H4350 and H4831SC are commonly used in the 6.5x284. A lot of shooters prefer Vihtavuori N160, N165, N170 and there are just as many who prefer Reloader 22, Reloader 25 and Hodgdon’s H1000. Since we already had two-eight pound kegs Hodgdon’s H4350 on hand, we decided to use it for our tests. We are admittedly partial to Hodgdon’s powder, having used it in our hunting rifles for over 40 years.
Range of Powder Loads: Here again, depending on the powder, the possibilities were mind boggling. Most F-Class shooters recommend keeping your velocities between 2,950 fps and 3,000 fps. The 6.5x284 barrels burn out fast enough, without pushing the bullets to their maximum velocity and accelerating the process. (2950 fps is at or beyond the top maximum load listed in every reloading manual I own! -Ed.)
The literature we reviewed suggested loads from 48.6 grains to 49.8 grains for H4350. We decided to start at 48.6 grains and work our way up in 0.4 grain increments to 49.8 grains.
We loaded three rounds each at the following charges: 48.6 grains, 49.0 grains, 49.4 grains and 49.8 grains. The bullets were “jumped” rather than jammed into the lands and grooves. Our chronograph tests were conducted at 5,232’ above sea level at a temperature of 90o F. As such, your velocities will vary in accordance with the environmental conditions in your area, as well as how you seat your bullets. We were looking for consistency and velocities above 2900 fps.
The following table displays the chronograph results of three shot velocities for the charges we loaded:
Lapua 139 grain Scenar
H4350 Powder 48.6gn 49.0gn 49.4gn 49.8gn
2969 fps 3033 fps 3038 fps 3054 fps
2983 fps 3028 fps 3037 fps 3052 fps
2964 fps 3039 fps 3033 fps 3041 fps
Average: 2972 fps 3033 fps 3036 fps 3049 fps
Std Dev: 10 fps 6 fps 3 fps 7 fps
Once again, do not assume that a small standard deviation with a sample size of three is going to be significant. It simply gives you a good starting point to run your 10-shot accuracy test.
Because the velocities of the loads at 49.0 to 49.8 grains were more consistent, we made the arbitrary decision to exclude the 48.6 grain from further testing. This was a judgment call in an effort to save some barrel life on the new 6.5x284. We loaded up ten cartridges at each of the three loads and headed for the range.
We also changed our testing procedure. We decided to shoot five rounds of each load to check for grouping or scattering. If the initial five rounds showed pronounced vertical and/or windage deviation for any load, we will not fire the additional five rounds. Again, this was a decision that was based on preserving barrel-life in the 6.5x284. Unlike the 6BR, which can have a competitive barrel life of 2,000 to 3,000 rounds, a 6.5 barrel may be “shot-out” in as few as 800 rounds, although the norm is more in the 1,000 to 1,200 range. It is easy to do the math and figure out that if you are testing many bullet/load combinations, you could rapidly use up a significant percentage of your barrel’s competitive life.
All three loads produced meaningful results after five rounds, so we ended our tests after expending only fifteen rounds. There was too much vertical and windage with the 49.0 and 49.8 grain loads, but the group with the 49.4 grain load was very nice. The five shot 49.4 grain group measured ¾” in size, which equates to less than ½ MOA at 200 yards.
The results of the accuracy tests are illustrated in the following targets:
6.5mm-284 load development test targets. Photo by Jim Clary.
It is possible that with minor adjustments of the 49.4 grain load, we might be able to tighten the group up even more. However, we decided to use it in Susannah’s next match. After that match, we will make a decision on whether we need to adjust the load before the U.S. Nationals.
Copyright 2008 by Dr. Jim Clary. All rights reserved.