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 like custom trigger groups 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 - Muzzle Device: ZEROED Muzzle Brake 5.56 - 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 - Hand Guard: CMMG EML15 M-LOK - Finish: Cerakote Standard - Charging Handle: CMMG ZEROED Ambi - Pistol Grip: CMMG ZEROED Pistol Grip - Buffer Type: AR15 Rifle/AI - Receiver Extension: CMMG A1 Extension - Stock / Brace: Magpul MOE Rifle Stock - Trigger Type: Mil-Spec Single Stage - Trigger Guard: CMMG ZEROED Trigger Guard - Safety Selector: CMMG 60/90 Degree - Magazine: Magpul 30rd PMAG - Weight: 7 - Length: 37.8