Adds +1 round to the 357 Sig and 40 S&W; Capacity will not be increased on magazines with a capacity restriction feature; Will not fit the XDM series; These DO NOT FIT .45ACP magazines; These Pearce units blend with the contours and texture of the handgun and have a factory appearance once installed correctly; They are made from High Impact Polymer and withstand drop tests at temperatures from -20 F to 350 F; The added length provides better control & comfort while increasing round count