I have been using 26.9 grains of CFE with Everglades Ammo 55 grain bullets and Wolf Magnum SRP with good luck. Shooting them in a S&W VTAC II and Colt 14.5 inch M4 with good luck. Tried P-mags, D&H and Colt factory mag's on both and the bolt stays open when empty. I am not certain how a bullet profile could effect that .