S&W M&P Extra-Power Magazine Spring - Extra Power Magazine Spring For S&W M&P

Extra-length magazine spring replaces factory-supplied spring for use with aftermarket magazine extenders and extended base pads that increase round capacity. Gives follower up to 10% more power for smooth, reliable feeding of rounds. Made of certified aerospace-spec chrome silicon wire, then heat-treated and stress-relieved to ISO 9000 standards. Mfg: Brownells SPECS: Chrome silicon steel wire. Fits S&W M&P pistols chambered in 9mm, .40 S&W, and .357 SIG.