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. Explore RECOILweb:New AK and AR Magazines from XTech TacticalDaylight's End: post-apocalyptic urban brawlShield Arms Opens Pre-Orders for S15 15-Round Glock 43X/48 MagazinesSan Tan Tactical, Hornady, Proof Research Team Up for 6mm ARC Release with STT-15 Rifle NEXT STEP: Download Your Free Target Pack from RECOILFor years, RECOIL magazine has treated its readers to a full-size (sometimes full color!) shooting target tucked into each big issue. Now we've compiled over 50 of our most popular targets into this one digital PDF download. From handgun drills to AR-15 practice, these 50+ targets have you covered. Print off as many as you like (ammo not included). Get your pack of 50 Print-at-Home targets when you subscribe to the RECOIL email newsletter. We'll send you weekly updates on guns, gear, industry news, and special offers from leading manufacturers - your guide to the firearms lifestyle.You want this. Trust Us.