Interesting to note that the original nitro proofs are all on the tubes. Not very common to see that. Common on BP proof but not nitro...
The proof marks on the flats are all modern Birmingham standard proof. There is a date code in the crossed swords indicating the time of the reproof but I don't have the codes in front of me.
The gun is considered in proof if it is within .008" of the metric measurements. .008" = ~ 0.2mm