I've been working on developing a good 168 gn load for my SOCOM 16 for the past year; yes I said a year. I've had a lot of issues with my SOCOM and as I got more accurate with my ammunition I had to tweak the rifle more and more. I've finally gotten the rifle to the point where I can depend on the groups representing the load and not some mechanical aberration caused by the rifle.
I have tried three powders;
- IMR 8208 XBR
- IMR 4064
- IMR 3031
I have worked with two bullets;
- Hornady 168 gn A-Max
- Barnes 168 gn TTSX
Cartridge Overall Length;
Cases;
- Lapua
- TTL 2.006"
- Primer pockets uniformed
- Flash holes uniformed and chamfered
Primer;
I started out by using the Federal 168 gn Gold Medal Match ammo for a standard to compare against. My groups would vary, on the average, around the 1.25" size plus or minus about a quarter inch at 100 yards from a bench, using sand bags.
So far the two best loads have been with the Hornady A-Max bullet (I intend to find others that are more appropriate for hunting but the A-Max is a good standard for load development) and the IMR 4064 and 3031 powders. The loads were;
IMR 4064
- 41.8 grains
- COAL 2.82" (at the bullet tip) & 2.192" (at the ogive)
- Group sizes are averaging around 1.25"
IMR 3031
- 40.2 grains
- COAL same as above (have not tried other seating depths yet)
- Group sizes are averaging just a hair over 1"
The 4064 load is not at max pressures but going any higher doesn't improve the groups. The 3031 load is right at max pressure. At 40.3 grains I started pushing my primers out and by 40.8 grains the primers were blowing out on almost every round, I put the limit at 40.2 grains even though, according to my QuickLOAD software, the chamber pressure should be at about 49,000 psi. My guess is that the pressure curve for the gases just doesn't work well with the SOCOM barrel length. The muzzle velocities for the 3031 are slightly higher that what 4064 gives me (3031 seems to push the bullets about 50 fps faster) and the chamber pressures seem to be slightly higher with 3031.
I like the fact that 4064 seems to not beat my rifle up as much but I sure wish I could push the muzzle velocities up a bit while keeping the group sizes down. IMR 8208 is my pet powder right now and I might work with it some more now that I have worked the bugs out of the rifle and I have identified a valid, safe powder range for these other powders (this helps guide me when choosing a charge weight).