Bwaites,
Watched that video of the 50 BMG. After seeing it, I have to think that the load they shot was either one of the mild surplus military loads with a 647 gr class ball projectile or a mild handload. The reason, a braked LAR Grizzly will put you back about twice as far and hard with one of my handloads shooting the 750 gr A-Max at 2700 fps.
I have since sold that rifle and built my own on an AR-50 receiver in my 510 AM chambering which is a ***** cat to shoot but its also a 38 lb rifle with a 5" long 5 port muzzle brake that I machined for it.
To shoot any 50 BMG without a brake is well, stupid. The reaction of the "kids" shooting the rifle tells alot. Thrill seakers and thats about it.
Kirby Allen(50)