From google:

The appeal of the .50 BMG goes beyond just military and benchrest shooters. Many shoot the .50 "just once" to try it. It's a common misconception that .50 BMG has terrible recoil. Modern .50s usually weigh between 25 and 40 pounds and have very effective muzzlebrakes. These two factors together reduce the recoil to something more akin to the push from a 12-gauge shotgun than the hard recoil you might expect from a .300 Winchester Magnum in a light hunting rifle.

SEE PHOTO GALLERY
Watson's Weapons' The Boss uses an AR-15 receiver and mates with any AR lower. However, the action must be broken open to reload with a round in the bolt head.
The big muzzlebrakes work well, but they produce an extremely loud report and an area of overpressure blast. Once a shooter has had a visceral taste of what it's like to send a 650-grain bullet hundreds or thousands of yards downrange and see it smash into a target, his appetite has been whetted and he must own one. If you find yourself in this position, what are your options?

It used to be that the price of admission to the .50 BMG club was a rifle starting at about $5,000. In the last 10 years there has been an explosion in the numbers of .50 BMG options under $3,500. Many of these rifles have simplified frame construction or are built like tube guns, and many are single-shot bolt actions.

Sounds clever how they control the recoil.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.