I have had that problem also, buy a gun to go with ammo I had.
I have never played with anything smaller than .30 and that one was a peta.
It was a sewer pipe, but nice old English rifle.
If you have to make a gun to fit the wood, why not use some old 22 barrel and make a flinter, to see how/ if it works.
Than if it pans out , you can spend the big money.
There are old Milt training rifles with long barrels, but most of those are expencive or crap.
The money manger (you know who) would say, sell the damn wood.
But than I am deaf to good advice from all the shooting.
Good Luck