I seen to remember that some of the slide cracking was caused by using sub-machine gun ammo in the pistols? Could be wrong?
There was a 147 grain bullet with a subsonic muzzle velocity being used for submachine gun use (for use with silencers) that somehow achieved wider issue than intended vs the standard 115-125 grain supersonic bullets. Hey, if Special Forces use it it must be good right
However the heavier bullets increased the recoil speed of the slides of the M9.