Linseed oil will shrink into the pores somewhat over time. But the English guns that were used generally had oil added at the end of every shooting season. This would replace any oil that was worn away from handling.
Apparently there were traveling stock finishers that did this. Guns that hung on the wall etc that did not get oil added may show sunken fill depending on the oil used for the fill originally.
This comes to me second hand from a friend who had some conversations on finishes with Kit Ravenshear.
Using sanding dust in the oil will add solids and perhaps reduce shrinkage but its a PITA too for me anyway. Tried it and did not like it, no benefit for the extra work.
I think that a great deal of the "eye of Newt mixed with bat wigs applied under a new moon" comes from people who either were trying to make things appear more difficult than they were to generate business or people who had listened to to some such and then wrote a book or magazine article about it.
Then we have folks like Hal Hartley who, for example, used to char curly maple with a torch then sand it back to bring out the figure.
Monte Kennedy, Hartley, Linden etc did WONDERFUL work in checkering stocks but they were not Kentucky rifle makers for the most part and Hartley at least could not make a good Kentucky at least from the photo of his attempt found in Kennedy's book. They were "stuck" with post industrial revolution varnishes for stock finish. They wanted to "waterproof" the stock. This is virtually impossible but they tried (note the number of moderns sporting plastic stocks for this reason). The Linseed oil they had access to was NOT what was used as stock finish during the 18th and early 19th centuries and even much later in England from reports I have heard.
They were, for one example, using bar top varnishes then using a low speed buffer to take it off to fill walnut. Using varnishes with solvent bases, wet sanding etc, makes me wonder if they were addicted by "huffing" solvents. I don't think they knew any better. By their time "boiled linseed oil" was the stuff made for paint thinner or painting on board fences and was not suitable for finishing stocks in any reasonable length of time. They though that the hard "waterproof" finishes were good, but they do not work as well on gunstocks as on bar tops. Bar tops seldom see 100 degree temperature changes in the period of minutes as a gunstock can. When subjected to this many hard finishes will fail since they lack the elasticity that will allow them to move with the wood as it changes dimension due to temp changes etc.
The really shiny waterproof plastic finishes used for a time by Remington are the poster child for this. It as possible to actually hear the finish cracking. A friend told me of a hunter in a camp he was in bringing such into a warm cabin and it was possible to hear the finish tinking and crackling as due the temperature shock. The cracks then admit water freely.
Flat finishes that look painted on are another hallmark of "plastic oil" finishes.
Much of the hard, fast drying varnish technology comes from the advent of the industrial revolution and factory made finishes, usually for indoor use like furniture and wood work and the loss, for the most part, of the knowledge on how to make the old stock oils and varnishes. A true spar varnish is about as good as it gets for durability on a gunstock. But these are now chock full of aromatic solvents that are hazardous to your health.
As a result of this there is a great deal of hoop jumping done to finish gunstocks that is not necessary or even desirable. Factory made love the fast drying stuff they can finish stocks in their manner much faster and when making 200-1000 guns a day this is a factor.
I was watching the Outdoor Channel and the guy that runs Midway was polishing a stock. Of course he SELLS stuff so he spent twice as long and used 3 times and much stuff as needed and water as a cutting fluid. Yeah it will work but
Of course this is best if you use some cheap hard varnish or plastic sold as stock finish. They, in an earlier "infomercial" also recommend using 100 grit paper to remove old finishes and such
How to maintain the metal to wood fit was not touched upon IIRC.
Rottenstone and store bought boiled oil will do for cutting fluid, the stock finish is done to the point it will all be wiped off anyway. But most store bought "stock finishes" and furniture varnishes dry too fast for this so people use mineral oil, paraffin oil or water and of course this is recommended by the folks that SELL the fast drying varnishes that won't work as a rubbing lubricant and may not even flatten properly and thus REQUIRE rubbing out with the stuff they then sell for the purpose.
Heh heh heh. Its called marketing I guess. Its a win-win for the merchant at least.
Dan