polyurethane removal

[INLAND44]

Raw linseed oil dries much more slowly than boiled linseed oil. Tackiness starts to become apparent, IMHO, on the third or fourth coat even when cut with turpentine. Instead of being a clock watcher, be patient and wait for the coat to dry(!) before applying another else your haste will be rewarded by weeks or even months of waiting.

That's because it doesn't 'dry' and is not supposed to be applied in 'coats'. It is applied sparingly, being rubbed-in with a cotton patch or similar. The stock is then put away for at least overnight while the RLO soaks in. You can cut it with Turpentine which will speed penetration. If this will not penetrate your stock, it has some kind of hard finish that is clogging up the wood. If you get an old, black over-oiled stock, consider using Lacquer thinner on a ScotchBrite pad to clean it. For an existing unknown hard finish you may have to try the mildest solvent first as posted above - that would be the most conservative thing to do.