Mine had no trouble.
I had a HBAR that was not particularly accurate and heavier than it needed to be. He turned it down under the handguards to the A1 profile. I could not find a dimensioned drawing, so I had to borrow a rifle to go by. The one I got was very uneven, looked like it had been ground down freehand instead of lathe turned, but had a minimum diameter of .610". So FLG made mine .630" from the taper down from the chamber to the taper back up to the front sight/gas port bracket.
One of the 'smiths on AR15.com does it regularly. Maybe $75.