From NY Daily News:

Not in my hands. I’ve shot pistols before, but never something like an AR-15. Squeeze lightly on the trigger and the resulting explosion of firepower is humbling and deafening (even with ear protection).

The recoil bruised my shoulder, which can happen if you don’t know what you’re doing. The brass shell casings disoriented me as they flew past my face. The smell of sulfur and destruction made me sick. The explosions — loud like a bomb — gave me a temporary form of PTSD. For at least an hour after firing the gun just a few times, I was anxious and irritable.

The only reason it was loud was most likely due to an indoor range. If it bruised his shoulder it was because he wasn’t holding in properly due to poor instruction or ignorance.