There’s a world of options when it comes to AR15s and for those that want to reach out to further targets or hunt with 5.56 the 18-inch ENDEAVOR® Mk4 chambered in 5.56x45mm is an awesome choice. Despite all the different caliber offerings available today for AR15 pattern rifles 5.56x45mm still stands as one of the most popular. – Built on our Mk4 AR15 platform this ENDEAVOR can make use of just about any AR15 compatible component and utilizes a nitride-finished 18-inch 416 stainless steel barrel for enhanced ballistic performance. – Each CMMG® ENDEAVOR rifle is purpose-built for long-range performance with everything from the Magpul® MOE® rifle stock to the ZEROED muzzle brake and every part in between selected for its utility to the avid marksman. – The EML 15 handguard maximizes customization potential. M-LOK® attachment slots at the 12 3 6 and 9 o’clock positions give you plenty of real estate to mount accessories while the Picatinny rail sections allow for easy and solid mounting points for sights and accessories. – Platform Mk4 – Caliber 5.56x45mm – Operating System Direct Impingement – Barrel Length 18 – Barrel Twist 1:7 – Barrel Contour MT – Barrel Material 416SS SBN – Barrel Twist 1:7 – Muzzle Device CMMG ZEROED Muzzle Brake – Muzzle Thread 1/2 x 28 – Gas Port Location Rifle – Gas Block 0.750 Non-Adjustable – Upper Receiver Billet 6061 T6 Aluminum – Lower Receiver Mk4 Forged 7075 T6 Aluminum – Hand Guard CMMG EML15 M-LOK – Finish Cerakote – Charging Handle CMMG ZEROED Ambi – Pistol Grip CMMG ZEROED Pistol Grip – Buffer Type Rifle/A1 AR15 – Receiver Extension A1 – Stock / Brace Magpul MOE Rifle Stock – Trigger Type ZEROED Drop-In – Trigger Guard CMMG ZEROED Trigger Guard – Safety Selector CMMG ZEROED 60/90 Degree – Magazine Magpul 30rd PMAG – Weight 7 lbs – Length 37.8