In deciding how to finish a walnut stock I might suggest looking at how it was done pre-WWII. After all, your stock is intended for a gun that has been obsolete since the Grant administration. To me it seems inappropriate to use modern fast-drying finishes on a muzzle-loading rifle.
The Modern Gunsmith, Vol. I, by Howe. Chapter XII covers in detail of how a professional finished walnut in an earlier time. The procedure varied depending upon just what type of walnut he was using.
One may download Volume I for free at:
http://fliiby.com/file/34571/njz9evs5k7.html The term "Boiled linseed oil" doesn't quite mean what it says these days. Howe used real, raw linseed oil (you can't get it at the hardware) with real turpentine (also not available at hardware or paint stores). One finish involved mixing a pint of raw linseed oil with a half pint of turpentine, and heating to the boiling point. Apply with a swab. This is for an arm to see hard service, say in the tropics. After several heatings the oil became thicker.
Howe mentions how linseed oil was processed, some three or four score years ago. What it "boils" down to, is if you want good quality raw linseed oil in 2011, then get what is called "Cold Pressed linseed oil" from an artists' supply house. Oil already thickened with heat is available, same source, as "Stand Oil". Likewise real turpentine distilled from pine, no odd chemicals added, is also available. There are several types or grades of linseed. I would suggest staying with Cold-Pressed, possibly Stand Oil.
Background on artist oils may be found in
The Artist's Handbook of Materials and Techniques, Fifth Edition , by Ralph Mayer.
Artists' oil is expensive when compared with hardware store varieties, but not at all so versus commercial stock finishes.
For example: Lin-Speed $9.99 2 0z (59ml) dries in 2 to 3 hours. Advertised as "The Famous 'Real' Kettle-Boiled Linseed Oil." Source - brownells.com
I might beg to differ with the ad, but that's just me.
Winsor & Newton Cold Pressed Linseed oil $10.71 for 2.5 oz (75ml)
Winsor & Newton Stand Oil $6.30 2.5 oz (75ml)
Winsor & Newton Distilled Turpentine 2.5 oz (75 ml) $3.29, 16.9 oz (500 ml) $11.54
Source - dickblick.com
Real linseed oil contains no driers, so it requires some time to finish a stock. Hand rubbing is part of the process.