Served in the Army in the 1970s. Only time we were ever issued ammo (outside the firing range) was guard duty at the Logistics Center at Ft Lewis (15 rnds 5.56mm in mag, and the ammo was counted by the OD each time it was transferred! Mag stayed in the ammo pouch.
Guard duty at an ammo dump, in Germany, issued 5 rnds 12 ga. IN the tube, chamber empty. Guard duty at a tank park, barracks, or any other installation, you get a stick. If you're lucky.
Outside of hot zones (and sometimes inside them) the military is way more concerned with troops accidently (or on purpose) shooting something than they are with troops being able to defend themselves, or whatever they are guarding.
Exceptions are munitions, and nuclear weapons. Those they are kind of serious about.
Things may have changed some since, but I doubt it. Protection of the individual GI is always at the bottom of the priority list, if its on it at all.
All else being equal (and it almost never is) bigger bullets tend to work better.