After sanding and raising the grain 3-5 times and final sanding with 400 grit or finer.
Typical wood finish for maple is stained with ferric nitrate or "aqua fortis" stain.
Then real boiled linseed oil or a boiled linseed oil varnish.
But lumberyard boiled linseed oil is not recommended its not a stock finish as it comes from the can.
Probably Jim Chambers Flintlocks oil finish would be a good choice for folks not set up to make there own. I have not tried it but reports are good.
You can order ferric nitrate crystals from internet chemical suppliers. It better for the beginner than stains with an acid content as most "aqua fortis" stains bought over the counter have.
Mix with distilled water, apply to wood scrap. Allow to dry heat to develop the. Radiant heat no flame. I use a paint stripper gun, carefully. If color is OK apply to the gunstock. If not mix a little more crystals and try again. Or recoat the scrap.
May look pretty orange etc. but when oiled with a dark oil it will mellow out very nicely in a day or two especially if exposed to direct sunlight.
This stock looked pretty bad after I heated it but once oiled it came out very nice.
I would mix the oil with about 20% REAL turpentine that had been allowed to "air" in a shallow dish for 2-3 days before mixing. Mix well with the oil then apply all the stock will take. Set it in the sun for 10-15 minutes then wipe off any excess with a soft cloth. CAUTION the cloth will catch fire if it contains any significant amount of finish and wadded up. Put any such cloth/rags etc OUTSIDE away from any thing flammable and spread it out flat.
If a Walnut stock just oil with the mix it after sanding to 400 grit.
Follow up coats need not contain Turp some only mix a small batch.
Dan