From what I understand, it's not really designed for that kind of thing anyways. I mean, if you're built like Arnold or Lou Ferrigno, I suppose you could, but even if that were possible, I think the report from it as well as the waste of a very large bullet would pretty much defeat the point.
Nobody ever considered using something like that to be shot from the shoulder. I've fired a M82 Barrett from a bipod as intended and even then it weighed a ton. Something like that
needs to be heavy, otherwise it kicks like a freaking mule.
Same with the M-1 rifle from WW1. That .30-06 cartridge in a 1903 Springfield rifle kicked a lot, but when the M1 came long, it weighed almost twice as much as the '03 it replaced and it didn't kick that much.
I
have, however, shoulder-fired M-60s when I was an Army ROTC cadet on STX lanes (the M-60 was essentially gone from active units by then, but we used them along with M-16A1s that were handed down from National Guard units). I remember one time at advanced camp, we were coming up on a bunker complex and I was one of two M60 gunners (with with MILES gear emitters). The other guy hit the ground with his AG and went to work.
I, however, could see the OPFOR through the slits of a bunker and realized I wouldn't 'hit' them with the MILES gear from laying prone. So, I ran up to the bunker and fired it like a rifle into the slit. The lane NCO later yelled, "Cadet, what the [bleep] were you thinking, charging up like that. Do you think you're Audie Murphy?"
I calmly told him that I knew I could hit them standing up but wouldn't while lying down, and reminded him you could hear a lot of beeping coming from that bunker after I did that.
Stupidly, I then reminded him that Murphy was a LT when he was in the action from which he was awarded his Medal of Honor (which is something I often reminded NCOs once I became a LT later, just to mess with them). That NCO developed a vein on his forehead and he desperately wanted to write me up, but that he knew I hadn't actually done anything to merit that.
I never even saw an M-60 after that as all I ever saw were M249 SAWs in line units. Shooting one of those from the shoulder was impractical due to that giant box for the belt underneath it.