MR Inc. BFR

Magnum's BFR is a single-action revolver manufactured by Magnum Research. It is only available in stainless steel and is manufactured in a variety of heavy calibers, such as .500 S&W Magnum, including some traditional rifle cartridges, such as the.30-30 and .45-70/.450 Marlin. The name "BFR" officially is an acronym for "Big Frame Revolver". (However, collectors and large-caliber enthusiasts have been known to misinterpret the acronym)^[2

The BFR comes in two basic models, one with a long cylinder for big rifle cartridges, and one with a more traditional revolver cylinder length (called "short" by Magnum Research). Note that some models that use identical bores such as the .45/70 and .450 Marlin can be made with two cylinders for the same gun.^[3]

Magnum Research also makes these guns in custom calibers and discourages the use of most rimless cartridges in their revolvers due to mechanical issues. The BFR can be customized for the .50 Beowulf cartridge.^[4] These pistols were originally made by DMAX in Springfield SD until Magnum Research bought them out.

(Sources from Wikipedia)