Guns CMMG now offering 5.56mm caliber option for AR15 pistols Recoil Staff July 11, 2014 Join the Conversation CMMG is adding a 5.56mm option to its line of AR pistols. In addition to the new caliber, the Mk4 K AR Pistol features a 12.5 in. barrel (vs. the 8.2 in. versions in .300 AAC Blackout and 9mm). The new Mk4 K comes with a Magpul MOE grip and stock, an A2 muzzle comp and an ambi rear sling mount. The Mk4's rails are RKM11 free-floating KeyMod (slots at 3, 6 and 9:00 positions) with a Pic rail across the top. As with other CMMG firearms, the Mk4 K AR Pistol comes with a lifetime guarantee against defect in material or workmanship. Learn more on their website, Facebook page, YouTube channel or via Twitter. Notice: We Found Ammo In Stock: (Check our Current Deals page for more ammo deals - including bulk ammo) 5.56 NATO 55gr FMJ 150ct $129.99 Optics Planet9mm 124gr FMJ 1000ct $639.99 Palmetto State Armory 12ga Slugs 2.75" 200ct $259.99 Palmetto State Armory5.56 75gr FMJBT 200ct $198.99 Creedmoor SportsGet 5% off all Creedmoor brand ammo with code CREEDMOOR5 Disclosure: These links are affiliate links. Caribou Media Group earns a commission from qualifying purchases. Thank you! Explore RECOILweb:RECOILtv NRA 2017: Microtech SuppressorsNew: Gen 2 Delta Eagle JacketGone Shootin': Rockcastle Shooting CenterAnkle Carry Revisited