You can stain if you like, satin refers to the reflectance, like a flat finish or a gloss. Satin is between flat and semi-gloss. You can get polyurethane in any of these finishes.
You can buy it in a spary or small can size if you want to brush it on. I used a spary can to redo an old stock, came out very nice. One word of advise, sand sand sand very well because this finish picks up everything.
Sand to prepare the finish, Stain to get your color. Then your top coat is your protector. As stated before, satin is between flat and semi gloss. Avoid gloss finishes if you have imperfections. Flat and semi hide more sins than a high gloss does. Several coats of semi won't shine much more than two coats, but will protect better.
Companies like Minwax do sell stain/protectants that are one coat applications. I personally have limited experience with them and do not like them. I prefer the old sand, stain, top coat.
Definitely stay away from the combined stain/poly if you want a good, long-lasting result.
I've never redone a rifle stock, but I have done lots of wood furniture (re-)finishing. If you want to remove old stain, strip it chemically. Sand thoroughly prior to (re-)applying stain and let dry completely. Apply 2 thin coats of clear satin polyurethane gel with steel wool pads; sand in between coats with fine sandpaper (320 or higher). Use oil-based poly and stain if you want it to last.
Mike
"Eternal vigilance is the price of liberty." -Wendell Phillips, abolitionist, 1853
1) SAND the wood... you want to use a 220grit, then a 320grit... if you are going to sand out the old stain start with a 150grit.
2) Once the sanding is done you will apply a wood conditioner - wipe it on, wipe it off and immediately -
3) STAIN - using whatever color you decide on, wipe on a good layer of stain, don't get fingerprints in it, and wipe off excess right away.
(if it's not dark enough you can re-coat the STAIN until you get the color you want)
4) Sanding Sealer - now you lay on a coat of sanding sealer (shellac basically) to seal the wood for finishing.
5) SAND - a light sanding with 320 to get rid of any 'fuzz' and wipe/vacuum clean
6) POLY - I recommend "Minwax Wipe-On Poly" I just used this stuff on a mess of wood trim and it's great! Choose your finish SATIN (not stain) or GLOSS. SATIN is I think what you're looking for... You apply this stuff with a Pad (ask for STAIN pads at Home Depot) get the pad wet with poly, wipe it on with just a couple passes, THIN, with ONE full-length swipe. DON'T try to rub it in, just wipe it to coat it, then the last pass end-to-end to make it smooth and even. Hang it to dry at least 6 hours (they say 3-4)
7) SAND - just a touch with 320 to knock down any lint, bubbles, etc that may have gotten on. If you slide your hand over it, take a pass with sandpaper and slide your hand again you'll see right away how much you need to sand.
Repeat step 6 & 7
9) Repeat step 6 and let it dry a few days before messing with it.
You want to do at least 3 coats like this, cooler temps are better since the poly dries slower, which gives more time for it to lay flat.
The Wood Conditioner is to help the stain go on evenly, without you may get dark streaks in the grain of the wood - you can omit this if you aren't concerned with an even stain. (sometimes I like the dark contrast of the grain) The Sanding sealer makes a big difference in how many coats, and how well the poly lays on. USE IT! The Poly needs to go on thin, and without much working to not get bubbles and runs. - it would take me maybe 20 seconds to coat a stock. If you don't use the Sanding Sealer before Poly, you'll get much more 'fuzz' in the poly and need at least 2 more coats.
I would not suggest the spray poly, it works, but it is VERY temperature sensitive and difficult to get a nice surface. (no more than 60 degrees, and no sunlight) The new Wipe-On stuff is great!
All this really takes very little time, except the original sanding.
If you like the color you've got you don't need to do so much sanding, and can probably just get the old surface cleaned up, Sanding Sealer and Poly. (in this case you'll want to wipe it down with denatured alcohol before sealing to get any oils out)
Pete
"It ain't the guns stupid - It's the CRIMINALS!"
"Never try to teach a pig how to sing...it just wastes your time a - nd annoys the pig." - Robert Anson Heinlein
If you want the grain to stand out apply all the coats of Gloss Poly first. Then apply Satin poly as the final coat. If all the coats are Satin poly, the grain will be dull and not stand out at all.
The difference between satin and gloss is that satin has "dirt" (actually fine silica powder) added to it.
When finishing the group buy WASR-10, we had to apply five coats of gloss wipeon oil based Minwax poly. The first couple of coats made the finish look worse than the unfinished wood. It also absorbed a LOT of poly in the first couple of coats. It started to look better by the third coat. There was almost no absorption by the fifth coat. We did not apply any other sealer or stain as it is a AK47 rifle and AK47's should look rugged.