The “M” stands for “magnum” in the Benjamin Bulldog M357 — a high powered entry in Benjamin's Bulldog series of high caliber air rifles. The M357 delivers up to 300 foot-pounds of energy per shot, power 50% higher than the original model. To this magnum-level force, add an M18 muzzle adapter and an extended reservoir holding 440cc of air at 3,000 psi. Get all this in a compact, lightweight, well-balanced bullpup, making it one of the most powerful production .357 air rifles available. The M357 comes in an all-weather synthetic design with a five-shot magazine.