The 500 B&M is not in the standard line up of B&M Cartridges. It is or was more of an experiment and something to play with. The 500 MDM is a 2.8 inch RUM case, at .500 caliber. The 500 B&M is a 2.5 inch RUM case. Both designed for the Winchester M70 RUM Control Feed action, long action.
At 2.5 inches one can load full length nose projection Raptors, with the added Talon Tip, and work in the full length magazine of a long action Winchester M70, RUM
