I've been doing some research on this.

To summarise what I have learned: "For long term reliable ar pistol functionality buy a 300 BLK". Every bit of data I can find for 5.56 pistol at the velocity the bullet needs to perform to specification is razor edge thin in terms of safety. +,- 1/10gr carries a warning to let someone you don't like test it first.

No shit.


. . and this from a guy that spent a couple of hours this morning putting 48.5gr of H110 under 240 grain pistol bullets.