mostly wt of gun and ammo, but also the better controlability of M16 on full auto. You CAN'T fix what's wrong with 308. It's heavy, bulky ammo, no .22 unit, no concealment, no 1 hand utility, scope base for M14 sucks, and it's not the GI rifle rd, doesn't use GI parts or mags. It's been history for 35 years now, let it go. The military gets to fly and haul stuff, you have to hoof it. They get to go to safe bases in between wars, you are stuck with where you are. you have to forage, they don't. 308's power is wasted on men, so why bother to lug it around? EFFECTIVE cans for 308 RUIN handling of the auto rifles. A 10" CAR-15, with an 8" can on it, is every bit as handy as the uncanned 30 Carbine ever was.