I'm looking for some advice on lapping a conical loading tap, as it's something I'm not very good at. The gun is an early Webley Osprey. I have made some attempts, but at the end the tap is very prone to binding (suggesting high spots, I would guess).

Do you guys lap the new tap from the very start, or do you size it down a bit first, such as on a drill/lathe with emery or wet and dry?

What do you use for lapping paste? I've tried valve paste, but found it very harsh, then rottenstone in oil, which seemed much better.

Do you do it all by hand, or by mechanized means?

What kind of finish do you aim for on the final surface?

All tips and advice appreciated!