Random thoughts...

Always wanted to use one of these. https://www.youtube.com/watch?v=TsI3fHUOlQM

It is a 14.5x114mm round. Twice the muzzle energy of a .50 BMG round. The rifle itself weighing in at a good 20kg/45lbs. So him being able to stabilize the rifle when shouldered is impressive in of itself.

The weight of the gun helps with recoil but holding up that much weight like it's your standard rifle is real impressive.

Well I hate to be the nerd here but he’s actually not using much strength he’s using proper combat form to absorb the recoil when he’s firing just watch how it positions his body. If my guess was that this guy was probably Russian special forces or something he’s definitely using military form

Well the ptrs is a ww2 anti tank rifle, so not something special forces would be using nowadays, my guess is that the guy is a collector and got it as a surplus rifle.