A few years ago I put together some tips on "freshening up" and old shotgun to use as a shooter. As far as I can tell nothing I recommended would cause any permanent harm if someone wanted to do a later full-blown restoration. Doing this work typically has taken from 2-3 hours over a period of days and cost between $20-$30.
Steve
First do no harm Ive found that its easy and cheap to make a tired gun look a lot better by doing a few simple things.
Be sure when you take the gun apart that all your screw drivers tightly fit the screws so you dont bugger them up. Also, clean out the screwdriver slots on all screw heads before attempting to remove them, its amazing how much unseen dirt collects in the slots.
Stock I remove the stock and soak it for 12 to 24 hours in acetone, this will remove the old finish and much, if not all, of the soaked in black oil staining around the wood/frame area. After I let it dry, I rub it down with 0000 steel wool* and start wiping on very thin coats of True Oil. I let it dry between coats and then lightly rub the stock down with steel wool again before I wipe on the next coat of True Oil. I repeat 10-15 times and I always rub the stock down with the 0000 steel wool after the last coat to remove that cheap lacquered-look shine. Be sure to only give the checkered areas only 2-3 coats since the valleys fill up.
For cracks I use epoxy, I first spread the crack open as far as possible, then use one or more toothpicks laid on their side to keep it propped open. I next take slow curing epoxy and squirt it deeply into the crack with a disposable glue syringe (Hobby Lobby) then I take compressed air and blow it farther into the crack and then repeat with the glue syringe. I finally remove the toothpicks, press it together, wipe off the excess glue and wrap it with an old bicycle inner tube or rubber surgical tubing and let the epoxy cure for at least 24 hours. In some cases if need be, Ill drill and tap a small hole and screw in a thin stainless steel machine bolt slathered with epoxy. Ill pre-notch the screw with a file so I can break it off just below the level of the wood so it can be concealed better. I usually try to place any screws under the locks or the tangs. Through checkered areas is good since the checkering can be redone to hide the repair.
Metal frame and barrels I rub it down with light oil and 0000 steel wool to remove rust and grime. Ive also found that soaking the action overnight in Coleman Lantern fuel will clean out most accumulated grime and goo. After I pull it out of the Coleman fluid I use a bottle of high quality spray lubricant and one of those long red nozzles to spray lubricant into the recessed areas of the action. I let it set overnight in a standing position so the excess oil can drain out, then I use my air hose again to blow out any remaining excess oil. Usually that treatment will get the action working briskly without having to take it apart.
Barrels (assuming black and not browned barrels) I take the barrels that Ive cleaned with a 0000 steel wool rub and hose them down with automotive starting fluid to degrease them (dont be smoking when you do this!), after degreasing I rub the barrels down with a good quality cold blue treatment. Cold blue doesnt hold up as well as a rust blue, but its simple to do (and redo the next season) and wont hurt the barrels if you want to rust blue them in the future. Overall, while not nearly as good as rust bluing (especially in a side by side comparison) it will typically make the gun look a lot better than it did.
So thats my free advice for the day, its always worked well for me.
Steve
* be careful using sandpaper not to round the edges of the wood where the metal parts and butt-plate fits, I try to not use sandpaper at all.
