I've shot an assault rifle that I can't remember the model of and I've also shot a pistol.
Seeing as I'm a kinda wimpy 13 year old, the rifle feels like solid lead and even the pistol's recoil made my body ripple.
My grampa (pretty sure he served for WWII) also had a humongous, tremendously heavy belt-fed machine gun in an army crate. Pretty sure if I tried to fire that monster I'd dislocate my arm.