Most types of ammo in the game can be used with multiple firearms.
223 (Sniper, LSW, 223 Pistol)
5mm (Miniguns, Assault Rifles)
10mm (SMG, Pistol, Pipe Rifle)
You get the idea.
But 45 and 9mm only get used in Grease Guns, and Mausers. I know these weapons aren't needed, and it's not really important, I just feel like they're missing.