I've shot lots of .50 cal Barrette rifles from the shoulder. What some didn't see was the muzzle brake on the front of the rifle that mitigates the recoil. The blast from that brake will clear anything on the benches nearby that isn't tied down and really anger the people shooting there.
The recoil isn't that bad. More like a 30-06 without a shoulder pad.
My friend has one we use when our range sponsors a Women on Target program. The last stage is touching off the .50 cal. Everyone is afraid of it until he lets his 14 year old daughter at that time fire the first shot.
Nobody gets off the shooting bench without a big smile on their face after firing off one of those beasts.
Why he shouldered it that way is weird, and the stock is weird as well.
It's just like being in the middle of an explosion without being hurt in the end.