One of the headaches of shortened Stoner system weapons is that it was originally designed for a 20 inch barrel and when the Army decided to implement the XM-177 and the E2 follow-on, it had to add a heavier buffer and have a different gas port size. This ended up making the weapon more reliable when fired, but increased the stresses on the bolt and BCG. This is also prevalent in the M-4[A1] and commercial variants. When you go to a Springfield Saint pistol with the 9 to 10.5 inch barrel, again the stresses go up even more and was the gas port adjusted for proper lock dwell time. If not, one has premature unlocking while the bore pressure is high and this can cause catastrophic damage, even to Mil grade parts. Extractors begin to tear off cartridge rims. The new 5.5 inch barrel is more so affected. The muzzle blast is terrible and the gas column is not fully burned inside such short barrels, unless the ammo maker has compensated for it and I don't know any large makers who has yet. I'd want a can on one if I carried such a pistol. Keep in mind that the lethality of the round decreases dramatically as the barrel length in reduced towards 5.5 inches. Such a barrel might make 2,100 fps if one is using the M-193 55 grain projectile. I don't have the muzzle energy figures at present. A FN 5.7x28mm P-90 wouldn't be far away.