As Ken said, you will most certainly cover the $120 investment with the realized selling prices of the vintage double barrels by knowing wall thicknesses.
You will also avoid potential liability for a. selling an "intrinsically unsafe" product if something bad happens or b. something bad happens after the purchaser modifies the barrel. Selling the barrels "as is" is no protection.
Besides the liability, you could potentially recoup the gauge cost by avoiding the return shipping charges when someone discovers they've been sent a honed, unsafe set. Let alone the increased value the tubes would have if a buyer actually knows they are safe and usable. Better to know what is arguably the most important aspect of your inventory. What's that we always say? That stuff about having new toys checked out by a competent doublegunsmith?
