A couple of months ago, we built a 7mm SAW for one of our long time customers, and he sent us some Alpha Munitions .308 Winchester Small Rifle Primer brass to use for load development in his rifle. It was extremely consistent stuff and worked very well for his build, so I decided to run some in my personal 7mm SAW as well and let y’all know the test results.
If you’ve read other information we’ve put out about this cartridge, you know that we designed it around the Lapua .308 Palma Case. In comparing the Alpha .308 SR brass to the Lapua, the two lots we have tested are every bit as consistent on weight as the Lapua offering. The Alpha brass does have slightly less internal volume; my test lot averaged 53.4 grains of water versus 54.6 grains of water for the Lapua Palma. Also of note is the Alpha primer pockets. They are just slightly tighter than new Lapua pockets, which should help with even greater brass life. If you are using an adjustable jaw priming tool such as the Forster, you’ll want to ensure that the priming tool’s alignment to the pocket is perfect to avoid damaging a primer during seating.
To form the cases to 7mm SAW dimensions, I used our custom Whidden Gunworks die set and a 2 step form process that has proven to work very well for me. First, I debur the inside and outside of all the necks, put a sparing amount of One Shot sizing lube on the cases, and then run all the cases through the Whidden sizing die, with a .325″ Neck bushing installed and the expander removed. For the second step, I install a .312″ neck bushing in the die and re-install the expander ball positioned as high in the die as it will go without interfering with the bushing. This keeps the case mostly supported by the die as the expander passes through the neck on the return stroke. I then run the cases through the .312″ bushing, which puts the neck to it’s final dimension. This method yields formed cases with very little runout, which are ready to load and as the test data below indicates are more than capable or producing match ready accuracy on the first firing.
I’ve been building a load for my rifle to complete at the upcoming Precision Rifle Series match at Q Creek Ranch in Wyoming, and settled on the 180gr Sierra MatchKing bullet and Alliant’s new Reloder 16 powder. With my existing Lapua Brass, 44.5 grains of RL16 produced muzzle velocity of 2700 FPS and extremely consistent accuracy at all ranges. Here are the specs of my rifle:
- Bighorn Arms TL3 LBRP short action
- Bartlein 1-8.5″ #23 contour barrel, 26″ length
- McMillan A5 stock
- WTO Mk2 brake
- WTO short action bottom metal with A/W mags
- Huber Concepts 2 stage trigger
- Kahles K624i with SKMR3 reticle
- Hawkins Precision Heavy Tactical rings
This barrel currently has a little over 2000 rounds on it, and has shown no velocity change since initial break in. Based on the load already developed on Lapua Brass, I decided to run a test on the Alpha .308 SR brass to see if equivalent accuracy and velocities were achievable. Taking into consideration the reduced internal volume, I shot a modified ladder test with Reloder 16 to determine maximum pressure.
180 SMK, 2.950″ OAL, CCI #41 primer, Reloder 16
- 43.0 grains: 2651FPS, no pressure
- 43.5 grains: 2690FPS/15ES, no pressure. .7″ group at 200 yards
- 43.8 grains: 2702FPS/5ES, slight ejector mark on case head, easy bolt lift. 1″ vertical group at 200. Established as max charge for this brass/bullet/barrel.
With a good load found at 43.5 grains of RL16, I loaded a few more and decided to do some longer distance testing. I had several customer’s rifles to collect field data on the following morning, so once done with them I pulled my rifle out and shot two 600 yard groups. Conditions were 75 degrees, with a 12-15MPH full value wind from left to right. The first is the group pictured at the top of this post. The highest shot was the cold bore, followed by the two stacked together slightly below. Total group size measured 3.2″ center. I followed this group with a second group at 600 yards using my established load on Lapua brass. The second group was shot on a warm barrel, and measured 3.4″ center to center.
Later that evening, I pushed both loads out to 1055 yards. With very similar conditions to the morning shoot, both produced 5 shot groups hovering right around 6 inches, which I was more than pleased with. Of note in the 1055 yard groups was that the Alpha brass load seemed to steer better in the wind. While both loads exhibited about the same vertical dispersion, the Alpha brass load all fell within about 2.5″ horizontal dispersion. This may simply have been caused by more consistent winds or better calls during that string of fire and have nothing to do with the brass itself, but I plan to continue side by side testing to see if this is an actual trend.
In summary, our testing showed the Alpha Munitions .308 Winchester SR brass to be a very high quality and useful alternative to Lapua brass for 7mm SAW shooters. This test also answered a relatively frequent question on this cartridge of “can you really get match grade accuracy on the first brass firing?” Unequivocally, yes you can!