I have been using an Armalite AR180B for many years. This model uses an AR15 fire control set. Mine has a LaRue Tactical. I had my gunsmith cut off most of that ugly 'wart' on the muzzle, and install a regular AR muzzle brake. It takes AR magazines.
It has proved very reliable, as accurate as your standard type AR, and has good ergonomics. It has a gas operated, piston action.
[Linked Image from i.imgur.com]

Sam......