I've cycled multiple 20 round mags through an M-16 on full auto. BRRRZZZIIIP, drop the mag, insert another, BRRRRZZZIP, repeat. Nothing caught on fire, no malfunctions, no jams, everything just keeps on working. This was when I was employed by Uncle Sam, and the ammo was free. Load tracers, fire them at night and it's like a lazer beam, very cool. The only concern with going full auto with an M-16 is that you'll rapidly burn up all your ammo. A guy can only carry so much..