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