It really isn’t a force multiplier. It means in about 2 seconds everyone is out of ammo. The USMC abandoned it and went to 3 shot burst and haven’t looked back. And the semi mode is the preferred.
Full auto is amateur hour in any sane scenario.
I know it seems fun, but a full auto AR never outguns a semi AR. A bit less sexy, but with the money you save just go to the lingere section at Walmart and buy yourself something.
We are not talking about sane times.
I agree that full-chat is best saved for very special occasions, nighttime when other folks are making muzzle flashes, [get yours out quick then move!] when entering a hostile room, ideally after prepping it with a grenade in first, in rain or sleet when sights are more or less worthless, and when a guy with two .50 ammo cans rigged as satchel charges is climbing on the back deck of your tank, has both hands occupied and well away from his clacker hand detonator and you have an M3A1 greasegun in your hands because your tank commander borrowed your .45 autopistol because he could wear it under his poncho. the .45 pistol would likely have done fine, as would a shotgun. But a dozen rounds of .45 in a row worked okay.
If you have two guys with rattle guns, one smart answer is one on semi,one on full. and remember, we're talking a world with a LOT of rookies with no concept of sights, aiming or the slightest rudimentary marksmanship. Shotguns for such are really a better choice, but I promise you there won't be enough to go around, nor enough ammo.
Where full auto is useful is hitting running targets crossing your field of fire.Just pick a point in front of your target and fire.
Having said that,my weapon of choice if the SHTF is my M21 clone with Leatherwood scope.For close work my suppressed Mp5A3.