Used Glock, M4 and SCAR in vegas. The M4 was great.
Still not sure what a SCAR is.
Fabrique National (FNC) came out with a 5.56mm carbine to replace the M-4 (SCAR-L) and a larger variant in 7.62mm (SCAR-H). These use a gas-piston system instead of a direct gas impingement of the M-16/M-4. It runs cooler and cleaner, but it’s heavier, more complex and more expensive. Special Operations units have adopted them is some quarters.