These are space age composite poly/fiber 80% lower receivers.
The JMT receivers are super strong and have a very nice finish to them. They really are the Rolls Royces of alternate material lower receivers. Also, they’re quite easy to finish with an end mill bit an a drill press.
The receivers come with their own one time use jig and intructions for finishing them are available on the James Madison Tactical website from this link:
These are non returnable if any work has been done on them. Once you start drilling ormilling then it is no longer an 80% receiver.