Wide range of round compatibility including .223, 300 AAC, .224 Valkyrie, 7.62x39, 6.5 Grendel, .308, 6.5 Creedmoor, 7mm, 300 WM, 300 PRC, 6.5 PRC and more; Includes a small and large caliber polymer body with adjustable spacer system for maximum compatibility; Spacer system uses Mil Spec washers and O-Rings to offer the perfect fit; Can be mounted using M-LOK or the accessory holes on the side of ACC chassis; Reversible design allows for mounting on left or right side of chassis; Staggered design providing greater clearance around ejection port; Glass filled Polypropylene polymer body