Advantages of a rubbed oil finish are ease of maintenance and repair, wood stability with atmospheric moisture changes, and appearance. It's a life time finish. It will never yellow with age, chip, or crack because there is virtually no finish built up over the wood.
"Hand rubbed oil" is often misunderstood. There are plenty of people that espouse doing a hand rubbed oil finish by working the oil in with the palm of the hand for an extended period of time to "heat it to aid penetration". Capillary action is what really draws the oil into the wood, and working it 'on' by hand does nothing additional for getting it 'in' to the wood.
The hand rubbed oil nomiker comes from two things: prior to the advent of lint free paper towels (Scott shop towels for example), the finger was the best lint/dust free applicator available, so in a sense that part is true to the process's name of 'hand rubbed oil', but that takes a minute and no skill. The real rubbing however is in the removal of the cured finish back down to the level of the wood, because the real goal is to fill the grain pockets with oil and not leave any oil on top of the wood. Applying is easy. rubbing it back down again with sand paper is not so much, and you will quickly learn that it is the rubbing off that is the work, not the rubbing on.
In the traditional methods, only one thin coat is done at a time to minimize the build up of corns during the sanding. Corns are balls of dried but still soft oil that gets 'rolled up' on the surface of the wood and clogs the sandpaper. The rubbing off of dried oil was traditionally done with steel wool, which sheds and can be left in the pores of the wood. In modern times Scotch Brite type scrubbing pads have been used. After having finished many stocks by both rubbing off methods, I have come to prefer sanding the dried oil off. It is far faster and far more effective. It's aggressiveness allows many coats of oil to be applied before rubbing it off.
This 'rubbing to level' of the cured oil continues through to the final polishing stages.
Overview of the process:
We are doing two basic things in the process of oiling a stock: First, filling the pores of the wood with oil to bring them fair with the top surface of the wood, and second, fairing the wood surface while we're at it. This is done in steps involving applying multiple coats of oil, letting it cure and sanding off most of it. Oil removal starts with 80 grit sand paper and progresses through to 500 grit paper, and the finish ends with rubbing compound, polish, and wax.
There are many oil formulations and recipes out there, primarly based on Boiled Linseed Oil (BLO) as a base, with thinners, driers, and UV agents added. My recomendation is Minwax Antique Oil Finish. When done, it has a lustrous shine which can be knocked back to a mat appearance with rubbing compound. As the finish builds to a shine, the colors come out of the wood bright and clear, really very good looking. Compared to other products, it dries quickly to a hard finish that cuts (sands) easily, and takes well to polish for a gloss look or rubbing compound for a matt look.
Pure Tung oil is to be avoided. Such oils never fully dry and are inappropriate for gunstock work. Varnishes and Shellacs are similarly to be avoided. While they cure hard and can be rubbed down, they are really intended for built up on-top-of-the-wood finishes and are not appropriate for gunstocks. One may choose to use a Polyurethane finish instead of oil, however note that polyurethane is particularly susceptible to UV degradation, spectacularly so. If you insist on using a Polyurethane, use a spar varnish that has UV protection. Spar varnishes by nature are quite thick, so expect to thin them.
Ultimately, for a long life finish and for showing off the wood at it's best, I highly recommend Minwax Antique Oil Finish.
I prefer applying oil from it's factory quart tin because it's small mouth makes it easy to control the tiny amount of oil that needs to be applied to the folded paper towel applicator pad. However, after a stock is finished, for long term storage of oil, pour oil out of the factory tin into a glass juice jar with a somewhat small opening. Add glass marbles (available most any place that sells flower arranging kind of stuff like vases. Walmart is a good option) until there is no air left in the jar. Wash the tin with mineral spirits for later use as a dispensing device. When finishing another stock, transfer the oil back into the factory tin with a funnel.
This is the kind of oil that you hear about autocombusting when rags are left in a pile. I'm sure it must be impossible for a small torn off piece of paper towel wet with oil to do that. But nonetheless, I open the folded paper towels and drape them over the edge of the trash can/bag and let them dry.
Wear a dust mask when sanding.
Note on wood filler:
Very often a piece of wood will have tiny (or not so tiny) voids or fissures in the grain; maybe a series of half a dozen grain pockets that form one tiny crevice, or maybe even a sharp corner, like at the top of forearm screw hole cutouts, is flawed or broken off and needs to be built up. Tiny voids can be left as is, or filled. I prefer to use laminating epoxy resin mixed with wood sanding dust as a thickener. Create a cup of sanding dust by holding a paper cup off the end of the belt sander and sanding down a piece of walnut. Do not use 5 min or 30 min. type epoxies; they cure too rubbery to sand well. Laminating resin dries crispy hard and sands very nicely. I use Tap Plastics 314 resin with the 102 fast hardener. Any similar product, like West Systems Marine Resin will work fine. Use an inexpensive digital scale from Harbor Freight or similar source to measure small amounts of resin and hardener. The 4 to 1 ratio is easiest calculated by zeroing out the weight of the cup, add resin, then multiply the weight by 1.25. The answer is the weight you need to add hardner up to. Use a paper or plastic cup that does not have wax. Dixie paper cups (but not the waxed variety) are what I use for small quantities.
Note on Sanding Slurry/wood filler
I advise against filling the grain with mud or making a mud by sanding the wet oil. The slurry is never the same color as the local area being applied to and will leave a speckled appearance to the wood. For the full color and figure of the wood to show through, fill the grain pores with oil only.
If you have never sanded a piece of wood from a rough carved state, it will appear to be a daunting, overwhelming task. Surprisingly however, walnut sands readily and easily. It is effortless to use 80 grit machine sanding belt material rolled in a curve and completely smooth, round, and shape the upward curving area around the cheekpiece. 120 grit on a sanding block will quickly shape long straight sections. Shoe-shining action with a strip of sandpaper will very quickly fair a rounded shape. It is NOT hard. None of what follows is beyond the ability of anyone willing to spend a 1/2 hour a night for a while.
After the very first three soakings of oil, the stock can be put into service, though strictly speaking the stock is not exactly 'finished'. You may choose to continue to improve the stock at any time by advancing through a few levels at a time, and putting the stock back in service the very next day for a while.
Note on recoil pad/butt plate:
(Note most stocks we carve will have the recoil pad fit and shaped. This information is included here to have a complete set of instructions).
It is best to cut the length of pull and mount the recoil pad at the start. Use the slack side (bottom) of a belt sander to shape the pad to the wood. As you will likely impact the wood a little bit doing this, it's best done early and leave the recoil pad on throughout the sanding and oiling stages.
Shape pad with a 6" belt sander with the platten vertical using the slack side rather than the platten side. Stand on something so you can look down on the work. Grind pad down to the wood holding the stock at a slight angle to remove pad material without hitting the buttstock. I.e., instead of holding the stock flat to the sanding belt, tilt the stock away from the belt a little bit. Sand the pad and wood to perfectly match.
Finishing without a recoil pad:
If the stock has been cut to the correct length of pull before finishing and without the recoil pad (as in an adjustable butt plate that does not fit to the edge of the wood), glue a sacraficial piece of wood on the butt end. I recommned a piece of 1/8 or 1/4" thick basswood from the hobby store. This will give you an over-run piece to round off when sanding instead of rounding off the butt end of the stock. You may choose to sand a chamfer around the edge when finished, but that will be much neater than the rounded edge that happens from sanding over the edge while finishing.
Scott Blue Shop Paper Towel
Regular paper towel
1" chip brush. These are the cheapest wood handle bristle brushes you can buy.
80 grit machine sanding belt material
Wire brush to clean out sand paper in early stages.
1/3 sheet sanding block like this from Harbor Freight for a couple bucks:
Mineral Spirits (for cleaning fingers)
3M 39004 Super Duty Rubbing Compound
Turtle Wax Polishing Compound
100% natural Carbauba car wax
Initial wood prep:
Use 80 grit machine belt or metal wet/dry sand paper cut into convenient sizes (rolled into a curve works for inside curves like around the cheekpiece or glue with 3M 77 spay adhesive to a small block of wood for flatter areas) to work rough areas and finish shaping the wood.
Use 120 grit sandpaper to work out the sanding scratches from the 80 grit.
Sand to bring the surface of the wood to a level below the lowest divot or carving mark. You will not see all the sanding that needs to be done until the first application of oil, but get the wood as fair as you can at this point.
What is important for sanding at this stage is that all the surfaces are 'fair'. In other words, if there is a small divot that needs to be sanded out, don't sand it locally to smooth it. This will only create a larger diameter crater. The entire surface of the wood needs to be brought down to the level of the deepest divot. In other words, if there is a divot in the forearm, sand the entire forearm down until the divot disappears. Use light pressure and high speed to glide over the divot or low spot until the surrounding wood is brought down to the lowest level of the divot.
Care must be exercised here to make sure that all flats are dead flat, corners are sharp and edges don't get rounded over. Sand with a sanding block to back up the paper and give attention to the maintenance of edges and corners.
Use a long strip of sandpaper like a shoe shine cloth around round areas like the bottom of the forearm and the top and bottom of the buttstock, and around the pistol grip.
Use compressed air if you have it available to blow out most of the sanding dust and rub the stock all over with white paper towel to remove dust from the pores of the wood. This will allow you to easily see areas of sanding scratches that need more finish sanding, and will prevent this dust from becoming part of the finish.
Soak outside of stock and all inletted areas with oil using a 1" 'chip' brush. Soak up excess oil with blue paper towel. Have mineral spirits handy and use it generously on the recoil pad if you get oil on the pad. You can even just pour some mineral spirits over the back of the pad to fully irrigate it and wash off any oil. The sanded sides aren't a problem, but you will likely get oil on the back, so wash that off. Let dry.
In a warm environment drying may take a day. In a cold damp environment it may take a couple of days. Some articles on the internet advise against hurrying the drying. I have experienced no ill effects and I highly recommend putting the stock in a very warm space (a 1/2 bath with a space heater is great) or in the sun. A hot car is a great drying oven.
Your nose can be an indicator of how it's doing. If most of it has outgassed through drying, there will be only a slight odor, and when totally cured, there will be no odor.
The first coats will take a lot longer to dry than later coats, as the oil is impregnated deep in the wood and doesn't come in contact with the air easily to outgas and therefor dry. Also, as you make progress, a moistened paper towel will go further and further, until you will only need to re-moisten it a few times to cover the entire stock when applying oil near the end.
First Sanding Off of OIl:
Corns are balls of dried but still soft oil that gets 'rolled up' either on the surface or on the sand paper. Corn buildup is your visual cue to your progress while sanding. If corns are rolling up on the surface of the wood instead of in the sand paper, you need to use coarser sand paper. When you are at the 320 stage of sanding, you may find isolated spots where corns will build on the surface. That is your visual cue that in that area, you need to use appropriately coarse paper to remove the excess dried oil.
Therefore the first sanding off is with 120 garnet or 80 grit machine belt material. Use a wire brush by hand to clean the paper of dried oil. You will have to frequently change to a clean section of paper, and change paper swatches frequently as corns build in the grit. Be willing at every stage of sanding to not be stingy with the sandpaper. When it's clogged or not cutting anymore, use a fresh piece. Yes, you will go through a package of each of the grits and you might spend $50 on sand paper by the time you are finished, but it's worth getting the job done and not spending forever sanding with weak, worn out paper.
Fairing the Surface
A significant aspect of this first sanding is making the wood surface fair. You will see low spots because they will be dark from oil while surrounding sanded areas are light. Sanding dust will collect in low spots as you are sanding, providing another visual cue.
Use compressed air if you have it available to blow out most of the sanding dust and rub the stock all over with white paper towel to remove dust from the pores of the wood and help expose areas of sanding scratches or carving marks that need more work. Once again use a chip brush to generously apply oil all over the stock and rub off with blue paper towel.
2nd sanding off of oil
Sand with 120/180 grit garnet paper. We use 80 grit machine belt paper because it is has sharper edges than garnet paper, but when we work at the 120, 220 and 320 levels, garnet paper is better. If you have an area that builds corns on the surface of the wood instead of collecting on the paper, switch back to the next coarser grit to remove the excess oil. You can also tell areas of excess oil buildup because it will look black and won't coat with sanding dust like other areas do. If you scratch it with a finger nail you can really tell the excess oil that's in that spot. Use coarse grit as appropriate to remove the oil from those spots. If the finer cut sandpaper is gliding over it and not sanding, all the sanding in the world with that grit won't remove it. You have to jump back to the coarse grit to get it gone.
Sand to remove all scratches from 80 grit.
As you are sanding, you can tell where exactly under the sand paper the wood is being sanded by watching the trail of sanding dust in front and behind the paper as you move it back and forth sanding. That trail of dust will show you where you are actually sanding under the paper.
You can spot divots that still need to be sanded out because they will collect sanding dust in the little pockets as you are sanding an area. Make sure to sand the entire surface down to the level of the lowest divot otherwise you will just make a larger depression.
Note on preparing blue paper towel for oiling:
Use Scott Blue Shop Paper Towel which is lint free. To prevent fibers from the edges of the paper towel getting into the finish, cut a square of paper towel maybe 4"-6" on a side with scissors to create a clean edge. Then to really make sure no fibers from the edge can come off, fold each edge inwards, then the whole pad in half and half again to hold the folded edges in place. You should end up with a small ~1-2" square pad with no cut edges showing. The pad will also be thick enough that little oil will soak all the way through to your fingers by the time you've wiped the stock with oil, making finger cleanup easier.
Apply a thin coat of oil with a folded square of blue paper towel. Wet the towel by placing it over the mouth of the oil can and tipping the can. This will moisten a small circle on the cloth. Rub it into the stock starting at one end. You will have to frequently re-moisten the cloth, perhaps only being able to wet out a couple inches of area of wood at a time. Work your way to the other end of the stock until it's all been wet. Now start over back at the beginning again and wet out the entire stock with another thin coat. Don't apply it thick and drippy; rub it on thin. And one more time, start back at the beginning. So you have rubbed on 3 coats of oil. Once again let cure (dry) in a warm space.
Transition to 220 grit. If you're balling up corns on the surface, use 180 in that area, then transition back to 220.
Use a foam backed sanding block as much as possible to ensure the surfaces remain fair. At this point you will see lots of low areas you didn't see before as they will remain unsanded and dark oiled looking unti you sand the surface fairly down to the bottom of the low spots. Additionally, lots of little carving marks and divots you didn't see on the first sanding will now stand out. Sometimes you can notice low spots as you are sanding because sanding dust will collect in the valleys. When you wipe the dust off you may notice them because they have a darker unsanded appearance.
Note: use 120/180 grit as necessary to work areas with particularly deep divots, then back to 220 to remove those sanding scratches.
Once the stock is no longer sanded back down to bare wood and is fairly well soaked in oil, wash the stock with a high pressure jet from a hose after a rub down before the next oil and let dry in your warm place.
Continue to oil three coats at a time and sand with 220/320, wash, oil, and sand again until as much of the grain pockets are filled as you're happy with. You can continue to fill the pockets with oil until they're all gone, or put the stock into service at any point and do more sanding and oiling down the road. As the pockets get very filled, and you think this might be the last sanding, use a piece of 500 grit wet/dry paper during the wash off to remove the 320 grit sanding scratches. After the next oiling, you probably won't actually be finished after all, but as the pockets get very close to being all filled, you may as well do a quick rub with the 500 just in case you are finished.
NOTE: one visual cue that an area has not been sanded enough is if you can not see the detail of the grain. It might be a nice walnut brown color, but if you can not see the actual grain richly glowing in an area, that is an area that needs more 320 sanding. As you sand, you'll see it looks like a smooth even light brown color, but when it's finished being sanded, you'll see the actual grain flow.
A visual cue as to how full the grain pockets are with oil is during sanding you'll see little glittering sparkly spots of oil in pores that have not been sanded. Sand down to the tops of the oil in those pockets, but not sanding so deep that you expose new fresh pockets to fill. If you can't sand down to the tops of them all without fear of exposing new pockets, do more oiling until there's enough oil in the pockets that you can sand down to them. When you do a light 320 sanding and there are no glittering spots anymore, the wood is completely filled.
Once the pockets are filled with oil as much as you have patience for (you can always come back later and do more filling and sanding) from this point on you are basically finished with garnet paper sanding. After the final sanding, apply one coat of oil at a time and let it cure. While before the oil looked wet when it went on but quickly looked mat, now you will have areas that stay looking shiny and wet even when dry. Continue to apply oil one coat at a time and let it dry until all areas look shiny. As some areas look finished, and other areas do not, you can just apply additional oil to the mat looking spots and not all over. There are always small spots that just refuse to take oil, so just keep applying and letting it dry until that small spot looks like the rest of the finish.
When you hit an area that you did a few moments ago it will be sticky and you just smudged that area. Just go over the entire area with the slightly dampened cloth and it will melt the stickier partially curing area and make it smooth again.
Rubbing compound is used to remove the dust that settles into the finish. Think of rubbing compound as being liquid very fine sandpaper. Use water and a wet paper towel and lightly rub the rubbing compound all over the stock. Wash, let dry, and re-rub areas that still have dust in the finish. If the wood ends up looking sanded, apply two or three more coats of oil as necessary to bring the finish back, and a light rubbing compound rub-down to remove dust that will be in those final layers of oil.
For a mat finish, you are finished.
For a gloss finish, polish the finish with Polishing Compound. Except note how it is not all that gloss, like a fake liquid plastic type finish looks glossy; the hand rubbed oil finish has a rich glow to it that can't be imitated.
Finally, wax the entire stock with 100% Carnauba natural car wax. This will allow water to bead off, and protect the finish from U.V.
Dents: Fold a piece of paper towel so as to create a triangle shape tip of towel two or three layers thick. Wet with distilled water (distilled to prevent mineral ring). Place over dent. Touch the tip or corner of a piece of steel or aluminum heated up in a propane torch or the flame from a stove to the paper towel. Hold the metal with Vice grips pliers. Test the heat by applying then heating more and trying again. You're looking for a heat level that will allow a fairly dramatic hiss of steam being generated. Re-soak the paper towel to keep it wet (the local applied heat it will dry it quickly and you want good water to create a good jet of steam). Do this repeatedly until the dent stops expanding. If it still has a small depression (which is likely) block sand the area smooth. Apply a fresh application of oil over the area with a piece of folded blue paper towel. Let cure. Repeat until it looks good, typically two or three times.
I much prefer heating up a small piece of metal as the iron. You can make it quite hot and get a real good steam jet into the wood very localized at only the dent that needs attention.
Scratches: Sand with 500 or 1000 grit, add a bit of oil, and rub with rubbing compound, and polish with polishing compound. Wash with soap and water.