Need to make chrome lined AR barrel legal by removing threaded portion. Barrel is chrome lined. Any issues ?

Can't you just screw on a thread protector and pin it?

No problems if you use a carbide bits. I have done this many times.

No cap and pinned is not legal
Chrome won't chip when cut in lathe ?

I would likely just turn the threaded portion down until the threads were gone. It'll look silly but there won't be any chance of tge chrome flaking.

That's thought and keeps a bit more velocity.
Thanks !

I've shortened and crowned several chrome lined AR barrels and never had an issue. The chrome is hard, but thin enough that it doesn't seem to really cause any problem with normal lathe tooling.