The problem can be if you get one of those really tight buggers, then a pipe wrench may not be able to clamp it and not damage the barrel. The bigger (longer) the pipe wrench the wider the jaws.

In that case heat would be the next option, but you need to know what you are doing

Then its cutting off with a dremel tool, but you also have to have a good hand with that so you don't cut barrel threads. They can be cleaned up but that's annoying.

Yours also has the bottom bolt release, it works, mine was plastic and I found it annoying. I converted mien to top bolt release.

That also is a bit tricky.