I'm seeing posts on this board and others where shorts are trying their best to confuse folks.
Let's make a few things clear. Ruger retired the AC556 a while ago. It was ONLY sold to police and military and it was a mini-14 model. The SR-556 is a semi-auto and doesn't even closely resemble a mini-14.
Before you let them confuse you more, do some research and you'll find that all AC models available are old and only available to buy on the secondary market IF you have a CLASS 3 dealers license.
Yawn, shorts are getting boring with their lack of knowledge or purposeful misrepresentation of information. Must mean they are getting desperate though.
While in the service I had a chance to shoot many weapons. My personal long gun was a 700 Remington in 308 caliber. However in certain situations we used the M-16 as well as the M-14. Both the 14 and the 16 were shot mostly on the semi-auto mode. Much more accurate than on full auto. Why you might ask? On full auto a gun barrel will tend to walk up. A .223 not as much as the bigger 308 nato round, but you tend to shot higher as the weapon is firing on full. Boy, I remember that 14 barking over those little .223"s popping. Even after 45 years, you might think I'm crazy,but I can still hear that beautiful old monster "taking charge" when I close my eyes. Ever get the chance, shoot one. As for me I'm just to old. Be safe.
Further to your point, a few years ago the military starting ordering M16s without full auto, only 3 round bursts and semi-auto settings. These are being phased in for most troops with only special forces having full auto.
Reason is simple, they did studies that found full auto a waste of rounds. Three round bursts are useful in close quarters where a rifle is cumbersome to aim and semi-auto (one round per trigger pull) is the most useful for short to medium range.
Military is finally catching up to what civilians have known for decades.
Of course the shorts and lefts will still lie and say semi-auto can spray bullets and that's dangerous.