While I am an avid user of linseed oil(generally mixed with dryers/thinners), I do agree with the notion that it’s not very good at resisting water. I think that treating the un-exposed inletting of a muzzleloader with one of the polymer based sealers provides a greater degree of sealing and protection. I have used both approaches On the inletting over the years and have, on occasion, experienced wood swelling and grain lifting using Linseed oil based products in the inlet areas exposed to water and moisture. IMO, this is one of the reasons for widening the the pin slots in the barrel escutcheons with a full stock flintlock. I do prefer, and will continue to use Linseed Oil based products(formulated with dryers) for exterior wood which alternatively may help to maintain the moisture content of the wood. I personally think the beauty of the finish is in a class of its own.
From Wilkapedia:
Wood finish
When used as a wood finish, linseed oil dries slowly and shrinks little upon hardening. Linseed oil does not cover the surface as varnish does, but soaks into the (visible and microscopic) pores, leaving a shiny but not glossy surface that shows off the grain of the wood. A linseed oil finish is easily scratched, and easily repaired. Only wax finishes are less protective. Liquid water penetrates a linseed oil finish in mere minutes, and water vapour bypasses it almost completely.[6] Garden furniture treated with linseed oil may develop mildew. Oiled wood may be yellowish and is likely to darken with age. Because it fills the pores, linseed oil partially protects wood from denting by compression.
Linseed oil is a traditional finish for firearm stocks, though very fine finish may require months to obtain. Several coats of linseed oil is the traditional protective coating for the raw willow wood of cricket bats; it is used so that the wood retains some moisture. New cricket bats are coated with linseed oil and knocked-in to perfection so that they last longer.[7] Linseed oil is also often used by billiards or pool cue-makers for cue shafts, as a lubricant/protectant for wooden recorders, and used in place of epoxy to seal modern wooden surfboards.
Additionally, a luthier may use linseed oil when reconditioning a guitar, mandolin, or other stringed instrument's fret board; lemon-scented mineral oil is commonly used for cleaning, then a light amount of linseed oil (or other drying oil) is applied to protect it from grime that might otherwise result in accelerated deterioration of the wood.