Parker Bros overload proved stamp

[Phil C]

Just throwing out the idea that possibly they batch proofed barrels an did this prior to assembly. It seems logical that you pull a few barrels from every batch and test them. If one fails more testing needed.
I also recall watching a vintage video where a whole row of barrels were tested using black powder and a fuse. Possibly just a initial test.
It would seem to me in a large scale production facility you would want the barrels tested well before you invest a lot of manpower assembling, laying ribs, marking barrels, and more finish work. Roll stamping barrels for example would also be much easier to do prior to assembly.
If you were building custom hand built high dollar one off guns that might be a different story.