The only shooter who knew what he was doing was the last one. He had the right stance to deal with that kind of recoil. Most of the others were standing like they were shooting a target rifle off hand, shoulders back, stomach thrust out, balance between the feet.

For that kind of rifle you need to take a trap shooter's stance, left foot forward, with most of the weight on it, shoulder held naturally, not thrust forward and anticipating the recoil, face firmly against the stock comb, butt firmly against the shoulder, just the way you would shoot a shotgun. Otherwise, it will bite you.

Be prepared to move the left foot to the rear without crossing over the right foot, then the right foot to the rear. It's a sort of little dance, which is not hard to master. It takes some room, however. This is better done outside, not over a concrete floor, just in case you lose control of the rifle, like most of these shooters did.