I have Newell's book "Gunstock Finishing and Care" and if I remember correctly good grade oil has a shelf life of about a year. He cautions that includes time on the seller's shelf so you want to buy from a source that has good turnover. I've had some luck with old oil on stuff that doesn't matter but I'm not taking any chances considering the time and effort that goes into finishing a gunstock.
He considered tung and boiled linseed about equivalent. I don't notice a difference anyway. He also liked a spar varnish finish rubbed down to the desired look. Old book, polyurethane was just coming on so he might've liked that for the clarity.
Now back to our regularly scheduled argument.
