I bought my husband the S&W 500 hunting model this past Christmas. It looks just like the gun in your photo, but IIRC, the barrel is only 13.5". Cool gun. The one you posted is a monster. What does BMG stand for?
BMG=Browning Machine Gun
Browning Machine Gun. I think that's not a REAL gun. It would probably break every bone in your hand, and several elsewhere. Surgery may be required to remove the front sight from the shooters forehead.
BMG stands for "Browning Machine Gun." This caliber is reserved for hearty souls firing Barrett rifles and hitting things at ranges normally associated with indirect fire weapons (mortars, artillery, nuclear weapons)!
Odd little note. The expression "the whole 9 yards" has nothing to do with football. I comes from the belted ammunition (.50 BMG) used in the P51 Mustang. When you "gave him the whole 9 yards," you fired all the ammo in the belt.
Cheers,