As a never-served fat and spoiled civilian, about the closest I've come
to trying a modern military rifle is getting to shot an AR-15.
It was amazingly smooth and rapid-cycling even if it was just semi-auto.
AR-15,.........varmint gun.
A lot is said about the weapons by looking at the safeties:
When you take the AK off safety, you're first placed on "auto". The user has to take an extra step to get onto semi; you get the feeling it was born to spray.
Doing the same thing with the AR first puts you on semi, where the weapon was intended to reside, mainly.
They're fun.
I legally own an M-16.Very smooth in full auto mode and not much more difficult to handle than a 9mm subgun.