Quick question on my MN 91/30, I stained the stock a few days ago, I've seen some people say they lightly sand after staining & before the coating (in my case tung oil), other How-to's online don't mention a sanding step between them.



So would it be a good idea or bad idea to go over the stock lightly with some 320 grit before the tung oil?

Yes.

Light sanding with 0000Fine brass wool, green scuffpad (careful, it cuts fast) or 600 grit paper between coats.



1st coats of stain and Tung oil will cause slight grain swelling, and fibers will stand up.

You just want to make sure it's smooth between coats.  You'll also knock down some dust particles too.  Look at wiping down with a 'Tack Cloth' after sanding.  It's sticky, and holds the dust.



I've used stain and oil, on stocks.  I've never used Tung oil on stocks, just building materials.



 

I have used Tung Oil for many applications and in your case do as above, after staining use 0000 steal wool to rub the stock down lightly. This smooths the stock out. After this blow it off with an air compressor or use a towel to wipe it down then use a tack cloth if at all possible to get the dust off.

Wipe on Tung Oil with a cloth of some nature that does not have much grain to it, like a sock cut in half.

I usually apply it generously since it soaks in on the first few coats pretty good anyhow. Just follow the grain of the stock and wipe in once direction, when rag starts to dry up just put more Tung Oil on it. Don't be afraid to apply it generously, but then again don't go crazy with it or you will get run marks that dry up and you will have to steal wool them real good to get them out.

I usually start on one end of the stock and do one swipe all the the way down, then work my way around while slightly overlapping the last area I wiped. After applying let it sit for at least 24 hours, I usually wait about 48 to be on the safe side so it has dried. At this point again use 0000 steal wool to lightly rub the stock down, then clean off and apply another coat of Tung Oil.

Keep in mind once you get to about the 3 coats you will see the stock not absorbing as much, at this point you either want to use the steal wool to dull the finish back down since the stock really won't suck up anymore of the Tung Oil ; or you can keep coating it and let it dry in between coats, after about 5 coats fully cured you will get a complete shiny finish. You can always come back and use the steal wool to touch a spot up and apply more Tung Oil, it will blend right in.

If you want a dull finish and an easier product to work with then you should consider Boiled Linseed Oil.

Same here, steel wool to get the excess stain off.

That doesn't make any sense

Steal wool is there to smooth the stock out not remove any material or stain.

This.




It's just to cut through the bumps from raised grain, dust that may settle on the wet finish, or a stray 'lump' of finish that wasn't dissolved in the can.
I prefer brass wool because it doesn't leave particles that may rust.  Corroded brass fibers have never been a problem for me.  And BLO (Boiled Linseed Oil), as was stated in another post by haLfLiFe.
My opinion, YMMV.
 

Yes, I don't remove any wood and I put stain on lightly so there is little to non that needs to be removed.

I've learned through trial and error making walnut stocks that, first of all, staining is not necessary on walnut if that's what you're dealing with.  The tung oil alone will darken it a great deal. What works best for me on a tung oil finish is to sand it to 150 grit. Then mix tung oil and turpentine 50/50 and lather the stock up with your bare hands.  After about an hour, wipe off any excess oil with a clean rag.  Wait about 3 days to dry, then sand it down with 220 and apply pure tung oil thinly with a clean rag.  Again wait about 3 days, then sand with 320, thin coat of pure tung oil.  Again 3 days, 400 grit, thin coat of pure oil.  3 more days or longer depending on humidity and temp. Just make sure it is completely dry.  You may like it right there.  It should  be a smooth flat finish.  If you want just a little more sheen, but not quite glossy, burnish with 0000 steel wool and put another very thin coat of oil on it.  After it dries, touch up any dull spots with 0000 steel wool again and rub a very thin coat of oil again with a clean rag.  I use pieces of worn out t-shirt for my clean rags.

I see.