Shellac varnish, often applied by French polishing, was by far the most common wood finish for furniture and other high quality items, until nitrocellulose lacquers for spray application appeared in the 1920s.
(You need to Login or Register to view media files and links) In my experience of original pieces finished by this method, it is quite durable and not harmed by handling. This finish is also easy to repair. On the other hand, cellulose lacquer over wood tends to craze, crack, and flake over time, and it is exceedingly laborious to remove.
Copal varnish in oil was in wide use for various purposes during the Victorian era, but I don’t think it was used for gun stocks in industrial production of rifles, where shellac based finishes were the rule. Here’s a typical gun stock varnish formula of 1890:
Varnish and Polish for Gun Stocks.— Gum shellac, 10 oz.; gum sandarac, 1 oz.; Venice turpentine, 1 drachm; 98 per cent, alcohol, 1 gallon; shake the jug occasionally for a day or two, and it is ready for use. Apply a few coats of this to your gunstocks, polish by rubbing smooth, and your work is complete. 1901:
Varnish for Gun Stocks-- Five oz. shellac, ˝ oz. sandarac, Venice turpentine 1 drm, alcohol 2qt. The French polishing method involves a small amount of linseed oil (a drying oil that hardens by polymerisation), mostly as a lubricant, but it becomes incorporated into the finish and may add to moisture resistance. Naturally, a gun stock finished with shellac varnish can be waxed for extra protection.