I thought I would do an update to my SOCOM 16 reloading journey.
I started this craziness with the idea of finding the heaviest load possible that would provide the greatest accuracy out to 300 yards. I set a standard of at least 6" groups at 300 yards. I modified my rifle so that I could eliminate it as the source of inaccuracy. The modifications include a JAE 100 G2 stock, an Ultimak rail, and a Nikon 2.5x - 8x Encore scope.
The result? The groups were inconsistent and varied from 1" to as bad as 4.5 inches at 100 yards using 168gr Federal GMM ammo. I spent almost a year working on this issue and found that most of the problem was the Ultimak rail was contacting the JAE stock in several places. I had to do a lot of material removal and trial and error until I eliminated all indications of contact between the two. A couple of months ago I finally got to a place where I felt that the rifle is now performing reliably. This is where I actually got a chance to start testing my hand loads. The loads now seem to repeat the group patterns and sizes and they respond to changes that I make.
So I started working on the heaviest bullet that I thought might work, 178 and 168 grain Hornady bullets, in conjunction with IMR powders. After many different tests I concluded that the barrel length (16.25") was too short to stabilize these bullets. I don't know if it is their weight or length but I suspect that the velocities and spin rate of the bullets were too slow to stabilize them. Now I'm working with 165gr Hornady GMX and SST bullets and they seem to be working the way I had hoped. Here is my most recent range trip and the group analysis results.
Range trip results from Sunday, 27 March, 2011. Time was 0900 to 1200 hours. It had snowed the night before and in to the morning just before I started shooting. Winds were zero and there were scattered clouds. Altitude was approx. 5100' and temps were around 35 degrees.
The rounds were;
- Bullet: 165gr Hornady GMX
- Case: Lapua, TTL 2.007", empty weights were 171.4gr to 172.7gr to help ensure consistent case volume.
- Primers: Win Large Rifle
- Powder: IMR 3031
- COAL: 2.81"
The powder charge weights varied from 39.6gr to 40.0gr in 0.2gr increments. It looks like my best charge weight will be at 39.9gr using these components and dimensions. I intend to test a different primer next and then adjusting the bullet seating depth. My guess is that I will end up with a load that can keep my groups at 1" to 1.5" and my muzzle velocity will be about 2515 fps. My QuickLOAD software estimates that my chamber pressure will be in the area of about 55,000 - 56,000 psi. My primers still look good but they are starting to flatten a little. I actually fired some of my older 168gr loads at 200 yards and got a 3.5" group; and those loads were not as accurate as these new 165gr loads so it appears that I might end up with 4" to 5" groups at 300 yards.
The groups of numbers within the parenthesis represent the position of the center of the group compared to the point of aim (POA). Notice that as the load went up the center of the group got closer to the point of aim. I stopped at 40.2gr of powder and I didn't post a picture of that group because the group became huge at that point (about 5.5"). Obviously the top end seems to be about 40.1gr of IMR 3031. Also notice that the standard deviation (SD) went from 15.3 down to 7. At 40.2gr the SD went back up to 12.