Hey Rich,
When using any finish on a longrifle, if you're getting runs, it means you're using far too much finish. When applying a finish whether oil or varnish, you should try to rub the finish in to the stock, not brush it in. As for removing the runs, I'd use some 600 to 1000 grit sandpaper with a flat wood backer to try and shave down the runs. Alternatively, you can remove your finish entirely and start over with a thinner coat. Runs won't happen because you applied too thin a finish, but too much. What kind of finish are you using? Best
-Eric