JCKelly, good, no,
excellent thoughts. While I understand the desire for "sealing" the wood, is it really necessary? At the armories at Springfield and Harpers Ferry, hot linseed oil was applied by dunking the stocks into the oil. Yes, it was a different linseed oil than we have commonly available today but there are a number of archived posts on properly preparing linseed oil to get what is a very similar product to what was used. Look especially for those by Eric Kettenberg and Chris Immel, there will be others as well.
stuart cee dub , you don't say what kind of "walnut stocked musket" you are building but you do say you want to seal it and maintain the appearance of the originals. Why not try the oil? If you look at original muskets from 150 - 225 years ago or any walnut stocked US military gun before WW2 for that matter, few if any exhibit cracks or swelling so the linseed oil on a
properly and well cured stock must have done the job pretty well? Military arms lead a generally tough and unsheltered life when on issue.
Personally, I have always used the store bought linseed oil and have had no problems with any of the muskets I have built over the years, but I have been trying to get the courage to try Chris's method of "boiling" the oil and hope to do it soon.
Now, you have been given some excellent advice above, better than mine for certain, so do what you feel is best after consideration, but there is a lot to be said for linseed oil applied to properly cured wood.
Sorry guys, I'll go sit in the corner now.....
Edit: Dave, I really admire the finish on the on the M1863 and the flintlock you show above, beautiful!