This thread as come a long way from the original red oil enquiry.
To keep it on track we really do have to differentiate between oil finishes and lacquer and polyurethane.Spar varnish does dry but is formulated to be flexible to cope with the rigours of a seafaring way of life.The usage your gun is going to be used for can determine the final finish.Is it going to be used for wildfowling, sporting clays or for display in the gun cabinet?