All rifles are loud, but the likely reason the AR-15 sounds so much louder is this little bugger right here.

It’s a flash suppressor. Its main reason for existing is to eliminate as much of the fireball that comes out of the rifle barrel as possible. It does this really well, but it also happens to direct a little bit of the gasses sideways into the range. Along with those gases comes a bit of the sound.

However, the guy that REALLY makes everyone angry is the guy that mounts one of these on their 300 Win Mag.

This is a muzzle brake and it’s designed specifically to redirect most of the gasses to the rear in order to help pull the rifle forward and reduce the recoil of the rifle.

Muzzle brakes work REALLY well at reducing recoil and some rifles, like the 50-caliber Barrett, would be almost completely unmanageable without one. The main reason people hate them is they are REALLY loud. They redirect so much gas to the side and rear that they can literally break stuff.