Magazines that stick out poke you in the back.
😁
Working as a United States Air Force Security Specialist (in the 1970's we were still using Vietnam era M-16's), I humped one almost every day for 4 1/2 years and never had that particular problem (maybe because I'm smaller framed than the average guy; I dunno). My big gripe with them was their propensity to get jammed. I saw it tons of time on the firing range so I can imagine it could be worse in an actual firefight. Used to drive the Range Masters nuts.