It’s always good to need as few different rounds as possible very good point. I’m not sure tho if they are worried about a side arm or not.
My SHTF prep is to arm folks with a rifle and sidearm in same caliber, from .22LR to 9mm to .357. My personal choice will be my Taurus .45 long barrel OSS DS. Have an M1 Carbine to accompany.