Have just watched the old Lethal Weapon film (Mel Gibson and Danny Glover), the first one.  I paid attention to ammo.  Their, presumably automatic rifles and/ or machine guns, seemed to have impressive loads and although a couple of times in the film you see them reloading weapons, much more you see a lot of gunfire and not only no reloads but no obvious place they're carrying extra clips.  (e.g. towards the end when Gibson and baddie are having a shoot out on the freeway and Gibson at least is wearing very little).  I suspect I should learn this kind of thing from Hollywood.