There are numerous ways to refinish a wood spear gun- All I suspect are correct. A few suggestions:
1) contact Al Biller for their recommendations and supplies
2) contact Jay Riffe who markets a special refinishing oil for his Teak guns
3) go to gun shop and purchase "LinSpeed" used for wood firearm refinishing
All of the above will provide an acceptable some what durable finish which should last for several seasons, but will need to be periodically refinished by repeating the process.
My grandfather, Sam I was born in 1856 on the Missouri frontier. I was fortunate to have been his constant companion during later part of his long life. One thing he taught me via OJT was how the pioneer hunters finished their fire arms-- repeated and liberal applications of linseed oil .
It is a process my son, Sam IV and I have successfully used for probably 40 years.
Purchase 2 bottles of linseed oil, one raw and one boiled--CAUTION Linseed oil is very volatile-and can erupt into flames -- be very careful around open flame and under no circumstances attempt to boil raw linseed oil to produce boiled linseed oil.
Procedure
1) apply liberal amounts of RAW Linseed by oil to wood -rub and massage into wood
2) when dry repeat the process - (generally in California sun every 2-4 days)
3) when wood reaches super saturation of raw linseed oil cease application of the raw linseed oil.
4) begin vigorous application of factory boiled linseed oil--rub and massage into wood
5) repeat process numerous times --
6) Allow to "Dry" for several weeks (gun will be sticky to touch- but will wear down )
7) Assemble gun
8) Stick fish
Both my shooting irons as well as son Sam IV are around 40years old and demonstrate only minor wear even though well used. I must give total credit to Sam I and to the pioneer process of finishing the wood with a protective bullet proof coating
Good Luck,
SAM