beleg2:
When the Enfield Breech-loader was first converted to fire the Snider cartridge, there were 2 proof loads for the barrels themselves. The 'first proof' was used on the iron barrels after forge-welding and consisted of 7 1/2 drams of powder and a 715gr lead bullet. The 'second proof' of 5 drams with the 715gr bullet was conducted after the rifling was cut. When the breech-loading shoe was fitted, the standard proof became double the service charge, which amounted to a 5 dram charge behind the 525gr bullet.

With regard to re-proving an old double, you're on your own! Sounds like a good idea, but I probably wouldn't do it personally.