If you are sure you won't go back to iron, then can epoxy it in place. Is a good place to use a cheap brand fast-cure epoxy...those are not as aggressive and are more easily removed if you change your mind (or sell the rifle and want to put it back to box-stock). Those types will usually give up when heated to a point where the metal "spits" when water is flicked onto it, but not so hot as to discolor the metal...the slow-cure epoxy types take a bit more heat...and the metal types (the ones that mix up to look dark gray) take a good bit more.
It's how the barel sleeve of a FWB 150 was put on...whatever they used (some commercail version of LockTite) is very aggressive....that one doesn't want to let go easily.
I've used a household over to get fast-cure expoxy to let go of metal (why does the torch always run out of gas just when you need it?)...just set the pover to 300degrees...let it get up to temp... put the metal work in for 10 min (with a full length barrel, you won't be able to close the door fully, but it will still work).