Spent a bit of time in choppers back in 1971 and considering that the metal between you and any incoming was not much heavier than a beer can.... my sidearm was the least of my worries... I was never a combat trooper, just a REMF hitching a ride in one direction or other, but never saw even a hint of a chopped carbine that year. You did see large number of regular carbines with ARVNs but that was about it...