I see. I wasn't sure if it was a patch puller or a wad puller. Of course a wad puller makes sense for a shotgun rather than a patch puller but you just never know what people might be using. If it were mine, before pulling the plug, I would try to shoot it out. Pull the nipple and stuff as much FFFF in as you can get, tamping it in with a small punch or nail until you can't get any more in there (it will probably only accept 5 or 10 grains), reinstall the nipple and shoot it with the muzzle close to or touching a cardboard box (to indicate if it came out). If it was a wire patch puller of course this would have no affect. Try that a couple times and if that fails then revisit the plug removal method. If you DO have to pull the plug, wood blocks similar to what Brent described is what is typically used to hold the barrels but, in the case of a double, the blocks must hold it FIRM. You could mitigate the torque on the joint by making a block that only holds the offending barrel and put that block/barrel in the vice VERY tight (and just ahead of the threads) leaving the other barrel outside of the vice jaws so if the barrel turns, the other barrel can swing rather than resist and cause strain in the soldered joint. Of course this means that you will be using the outside of the vice jaws rather then the middle where they are the strongest and MAY get flexing of the jaws unless you have a real skookum vice.
