I cross posted this at 68 Forums and I’m adding it here for posterity.
Here’s the rub: Twist rate makes ZERO difference to barrel performance. My earlier theoretical analysis appears to be supported and I expect that twist rates equal to or slower than 1:4 will see no appreciable difference in pressure or muzzle velocity. So far I haven’t seen any difference with 16″ 4-groove barrels in 1:7 vs 1:11 twist.
The numbers (mv in average of several shots):
16″ 6.8 BSP”
SSA 115 OTM: 2492 fps
SSA 110 TSX: 2547 fps
SSA 85 TSX TL: 3010 fps
16″ 6.8 SPC II 1:11″
SSA 115 OTM: 2493 fps
SSA 110 TSX: 2575 fps
I had exactly 5 rounds of the 85 TSX TL and didn’t have any left for the SPC II 1:11″ twist. I’ll get those next time. I didn’t measure accuracy closely but I was shooting about 1.25″ to 1.5″ at 105 yards with everything. Neither barrel showed better accuracy than the other. The brass looked exactly the same. With a suppressor or without, didn’t make any difference.
More testing will follow with the SSA Tactical loads