I have the xgrip for my m&p 9c and it allows me to use my 17 round mags from my full size m&p9 in the compact. The xgrip fits very well and actually closes the small gap that exist when the 12 round mag is seated in the compact. Taylor freelance makes a mag extension for 5 or 10 extra extra rounds of 9mm or 40 cal. A bit pricey.. the 5 round is 29.99 and the 10 round is 49.99. Brownells sells both the xgrip and the taylor freelance mag extensions. With the 10 round mag extension, I can get 29 rounds of 9mm in either the compact or full size m&p.