The MK12 Gas Block is only compatible with the RIS II (M4A1 & MK18) family of rail systems manufactured by Daniel Defense. It is not compatible with any other Daniel Defense rail system. This is due to various clearance issues. This only applies to rail system lengths that would completely shroud the gas block. If you are mounting the gas block to the barrel without being shrouded by the rail system, then this does not apply. In that case, it will fit as long as barrel diameter is .750.
All Daniel Defense products carry a 100% satisfaction guarantee against defects in original materials and workmanship. If your Daniel Defense product shows evidence of such defects, Daniel Defense will make every accommodation to fix, repair, or replace your product in the most expeditious manner possible. Daniel Defense does not warranty products or damage caused to our products by the correct or incorrect installation of other manufacturer’s products. Be sure to retain your sales slip as proof of purchase date when making a claim.