Arredondo Basepad & Spring for S&W M&P in 9mm & 40 S&W Arredondo Basepad & Spring for S&W M&P in 9mm & 40 S&W For High Capacity magazines only. Will not work for ten round magazines. Models: M&P 9mm & .40 S&W Extended Base Pad, add’s 5 rounds in 9mm and 4... MSRP: $24.71 Was: Now: $22.00