What do the letters on the back of American guns mean?

STD is a kind of guide rail that can be equipped with aiming equipment.

Saws are square and wear automatically, which is a class A machine gun.

Commando means commando, which should be designed more compact and convenient for special tasks.

Sopmod is a special modification of operation characteristics, and it is a widely used aiming and shooting system in the US Marine Corps.

Hb means heavy barrel. M2 is replaced by a heavy barrel. At that time, water-cooled radiators were installed in some areas of M2. Others changed it to a heavy barrel and named it M2HB, because the barrel is easy to overheat.