There is no reason that I can see to use raw linseed oil on any wood product, unless you are actively looking for a sticky surface to attract dirt. I grant you that this dirt attraction will highlight curl in maple over extended time, however I sincerely doubt *raw* linseed oil was used on any gunstock save perhaps those built in extreme backcountry areas. And frankly, even harder oil finishes will permit dirt infiltration, so raw oil has no benefit that I can see even in that respect.
Ditto for "tar." There were a huge variety of much harder and more refined resins available in pretty much any eastern area. Particularly various generic colophony resins which would have been even cheaper than tar, asphalt or Gilsonite based materials. All one has to do is go through store advertisements or inventories for Philly, Lancaster, Charlestown etc. Fully completed high quality vanishes were even available, let alone the very affordable primary components to make such varnishes or hard oil finishes. These were certainly not gunstock-only type materials so when you consider the large variety of woodworking and carpentry based trades using such materials, I personally find it a bit backward to consider the use of such primitive and unsuitable materials.
If one has access to "boiled" i.e. catalysed oil, why use a raw oil which is loaded with mucilage and other garbage that absolutely will not ever fully dry?
