You can purchase guns out of the stock/action/fore end section at Holt's for pennies, they are all out of proof and the barrels will have notches cut out of them but fine for metallurgical testing. I will be happy to import a few antiques for testing purposes free of charge. Drop me a pm and we can work out the details. This will likely be your most cost-effective method of sourcing tubes to test.
Steve

Firearms imports, consignments


[Linked Image from i.imgur.com]