FWIW - This is the answer that I have been led to
"the "accepted" standards for what twist is needed for what bullet are, for better or worse, thought of in relation to the standard 20" AR-15 barrel. Because your barrel is 26" long, you are probably getting close to 150 fps higher speed than the box states, about 190 fps faster than most AR-15 loads, and it's pretty **** hot loaded anyway. What that means is that you are likely doing a fair amount higher RPM than the "accepted standard", which generates an increase in axial rigidity; thus, the bullet shoots."