I believe we are going to end up with a cascade of complementary evaluation options based on ones toleration of uncertainty, and bank account smile :
1. External visual inspection
2. Internal visual inspection augmented by direct or digital images the length of the bore
3. Chamber length, forcing cone length, and bore measurements for evidence of alteration from the original
4. Wall thickness measurements from breech to muzzle
5. Non-destructive Testing (NDT); likely radiography
6. Proof testing to at least 1 1/2 times the psi of the shooters intended load

Anything else?

https://sites.google.com/a/damascusknowledge.com/www/home