I've done the sandpaper and socket method. I don't like how it opens up the top of the channel more at the top as you go up in size. What's the easiest way to open up a barrel channel? Mill? Would it be something the average gunsmith can handle? Is there anyone that specializes in that? Thanks!
How big are you trying to go? There are barrel channel scraper tool available from Midway and Brownells. You could use 40 grit paper and go finer as you get closer to the size you want.
It would be a substantial amount around the shank. Do those scrapers work on fiberglass?
You can also used wooden dowels wrapped in 40-60 grit paper. Removes alot of wood fast too.
Gunline channel scrapers. Fast, accurate.
The Gunline bedding tool is a must, but buy a set of replacement cutters if you're going to work on a laminated stock, 'cause the plywood glue is just death on the cutters.
Not sure what to use on glass. It might depend on how deep the glass wrap is. I'm thinking a round wood rasp unless you hit wrap then it's a problem.
Do those scrapers work on fiberglass?
They will but dull really quick
The sandpaper on a socket is the absolute best way to make any job look like garbage.
Cut under the top line of the stock with scrapers, chisels, even a Dremel or Foredom tool. For that last tiny bit around the stock line you can use files for fiberglass stocks; chisels and scrapers are best for wood.
Remember to seal the cut areas in the channel with a finish similar to the outside of the stock if wood. For fiberglass you also need to seal the channel as you will have exposed glass fibers which will wick water into the fiberglass.