The boys who build period correct flintlocks find that by properly boiling linseed and adding the correct driers produces a durable varnish which is consistent with originals. Linseed is the basis for most of the older varnish finishes, many of which have withstood centuries of use on both guns and stringed instruments. But if you are talking about boiled linseed as found at the local hardware - that isn't going to help you.