Pistol port is an inappropriate name, although it's intital design was for a defense use, it was rarely if ever used as designed. It was a very handy port to open and discard the shell casings that littered the turret floor, and it became its primary use. In every unit to which I was assigned, it was always referred to as the pistol port and I have never heard any other terminology. It was also very handy to empty the pp can, for which the loader was sadly tasked. It was welded shut in later stateside M-46s and discontinued as of the M-47 as it caused a weak spot in the armor.