A good man will admit his mistakes, and learn from them.

I made similar mistakes before. Theres solutions but it costs more and is more invasive than most people or I would even bother to do.

Or instead of sending it back… check with customer but thread the barrel to whatever thread is appropriate and make an adaptor to go from that thread to the one they want ? Will add length when installed but not much

I had a similar issue years ago when getting a tikka threaded to install a suppressor mount. The gunsmith made and attached an adapter of sorts and threaded that to the barrel to mount the brake. Actually looks and runs great and it’s well hidden by the mount and suppressor.

Machine the barrel down slightly and press fit an oversized piece, then thread it. Edit: you could pin it for more strength if you think a press fit wouldn't hold.

1/2-28 and adapter or correct mount.......easy

You usin seafoam as cutting oil? Good video 👍