Will this fit on an AR-18 lower? If it helps, the particular model I'm looking at is the ADM UIC-180. — 1 Answer

Yes it will. I have a couple fm15 gen 2’s, 2 Brn-180’s, mcx lt upper, and they all work with the picatiny buffer tube extension lowers from adm, brownells, foxtrot mike, and another one I got. If you are planning on suppressing this upper I highly recommend getting an adjustable gas block for it. FM offers upppers with them installed or you can get one from them, or at least used to. This is the only DI internal recoils system platform I’ve ever seen. I still prefer my Brn-180 but that’s because I’m a lefty and I always run a can. I have that adm lower, I got it on a bundle deal at brownells. FM products actually helped build the BRN-180’s along with PWS. PWS is the king of piston ar’s but they all have buffer tubes. FM is the only internal recoil DI systems. They worked together on it. I’m hoping that FM will start offering piston options, PWS has a new line of internal recoil rifles.