Raw linseed oil( Not boiled) makes a good lube for use with drill bits when drilling ramrod holes into wood stock blanks. Other than that, I would not recommend it for use doing anything else with a MLer.
It would certainly never dry, and it would GUM Up the works, as you say, terribly. You would have to use a good alcohol based solvent( denatured alcohol, Kerosene, Gasoline! etc) to get that linseed oil out of a barrel, along with all the Black powder residue it would hold in the barrel.