I have seen a gun come back from successful proof with 07 thou minimum!
Generally, a barrel with 17 or 18 thou is fine as long as it well up the tube. Just don't dent it and don't pay too much for it!
A friend of mine has a Purdey SLE with damascus barrels down to 17 thou. It is lovely and he only paid 5000 for it. I told him not to dent it. He has been shooting it happily for five or six years.
Unfortunately, he is too mean (cheap) to buy a decent gunslip and dented it last time he went out by banging it inside the gun bus.
The same gun with 25 thou in the barels would have cost him 10,000.
Take your pick.
Last edited by Small Bore; 01/11/11 06:32 PM.