The barrels are very pitted so I have been draw-filing them to get rid of the pits.
A It is very, very easy when draw-filing to get a bit carried away or overly focused on removal of the pits and forget about the rest of the barrel.
Finally, after completion of the draw-filing I would use some cloth backed abrasive to polish across or at 90[degrees] to my file strokes.
Because of that I began by draw-filing all the surfaces of the receiver.
Draw-filing is just the process of taking down a metal surface by pulling or "drawing" a file across the workpiece.
Of course, you can use other files for draw-filing.
When draw-filing a round surface, you have to be careful you accidentally create flats.