Carrot of Truth
War is Peace
Another IRL bullet that wouldn't make too much sense given the damage values ingame, although that one would be a lot more powerful than .22 short for sure.
We see from the assault carbine the magazine length looks about .223 size, not super short or anything, and rimfire in an automatic is a very bad idea.
The Vindicator does fire 5.56 but that still kind of retarded because then you might as well just give your dudes M60's. Dudes in Power Armor should be using autocannons since they are basically Infantry fighting vehicles on foot.