I believe that in U.S. small arms manufacture circa 1850-1920s it was accepted practice to proof test the barrels in a rough bored condition, prior to rifling and finish turning to outside dimensions. These used very heavy bullets to generate the desired pressures with the intent to burst any barrels with flaws before wasting time and effort finishing them. During the period when barrels were made by foldng iron or steel around a mandrel and hammer welding the longitudinal seam this was probably a cost effective test. Later methods of making barrels from drilled blanks instead of welding around a mandrel probably resulted in eliminating the practice which likely revealed relatively few flaws compared to the cost and trouble of doing the initial “burst” proof test, and only a final proof test of the finished barrel/arm was conducted.
While “auto-frettage” is certainly an accepted practice with artillery as outlined in the posts above, is it possible that the cartridge shown is actually intended for use in a “burst test” function, and not as a form of “auto-frettage?”
The U.S. Ordnance Department was notoriously slow to change processes, and the Russian inspectors in the U.S. during WW1 were obsessively picky about minor details, so this cartridge and its associated use may have been required “because we always did it that way” rather than for “auto-frettage” benefits.
Who has examples of the “burst test” cartridges used with U.S. arms manufacture for comparison?