Re: 308 vs 7.62 Nato
You make some very good points.
Something to remember is that not all "surplus" ammo is NATO ammo. NATO ammo is usually marked for year of manufacture, plant & also a circle with crosshairs.
The worst 7.62x51 (but not NATO) ammo has been that produced by India & it has actually blown up several rifles. Everyone & their dog produces 7.62x51 but not all is NATO & that means it's a crapshoot. It pays to be sure what you're buying.
The sticking issue you had was most likely not with NATO ammo. There is no more closely monitored ammo that I know of. Muzzle flash is not usually from overloaded ammo but lighter loads of ball powder. Shorter barrels can also help produce muzzle flash as in the Mosins. Sticking of re-loaded NATO cases is a possibility as the brass is thinner than with commercial cases-the reverse of normal when comparing military brass to commercial. Another way to identify NATO ammo is that it's all BOXER primed. If it's berdan primed it's not NATO but some kind of crapshoot 7.62x51.