Vintage Guns: Collecting, Restoring and Shooting Classic Firearms by Diggory Hadoke is a good start, for British Rules of Proof
A short preview is available
http://books.google.com/books?id=lvBk8df8PjUC&pg=PA139&lpg

Bore dimensions and marks post-1887 Rules of Proof
"At proof if a plug gauge of 0.729" diameter (but not one of 0.740") will enter the bore to a depth of 9", that barrel would have been marked 12."



So if the gun is marked 12, and a plug gauge of .740 can pass at 9", the gun is out of proof.

Yes, a gun with bore of .743 can be returned to the Birmingham Proof House for re-proof (and must be in order to be re-sold in England) and will be so marked. There are labs in the U.S. that will prove guns, and provide a report documenting the results.

H.P. White Laboratory, Inc. in Maryland and Cortland, New York will proof Twist or Damascus barrels for $500 (in 2014) to a pressure of 20,000 psi. A minimum pressure test would be 1 and 1/2 times the pressure of your intended load.
www.hpwhite.com

Chesapeake Testing
http://chesapeaketesting.com/services/outdoor-blast-testing/

Dayton T. Brown
http://www.dtbtest.com/Default.aspx

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