I want to lap a 22 RF barrel. The chamber end is almost .0015" tighter than the muzzle. Muzzle is .219+" measured on a slug, so it still is tight. Can I take this much out with a lap? What grit should I start with? Can I put a bit of tin into the lead to get a sharper impression when pouring the lap? Ball bearing lapping tool has been made. Plan on rechambering to 22 mag, so throat damage will be cut out when I rechamber. This is a Baikal22/20 ga, so not a benchrest quality job.

I think if you do a search here you'll find instructions on how to cast a lap and what compounds to use. You'll also find that just the idea of lapping is discussed quite a bit.

Good suggestion! Found 44 pages of lapping about 90% ring, and firelapping. Finally found a learned discourse from jurgen. 220 grit, and 200 strokes, and use a guide/fixture. Still can't find out how much 220 grit will take out, but I'm going to find out. My copy of Howe's and Dunlap's books have some useful stuff, too.

IIRC Vickery's "Advanced Gunsmithing" also has useful information on lapping along with how to rebore (freshen) a bbl. Say a 32-40 to 33-40

I worked with a guy that made/lapped barrels for a brand that was once well known in bench rest circles. He lapped with 220 grit and finished with 280.