J.D. Dougall information from the Internet Gun Club is here
https://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=399162
and
https://www.internetgunclub.com/forum/viewtopic.php?t=213

It was originally proved 1904 - 1925 (I think the 2 1/2" was marked at reproof), then reproved (Crown over R) by the date code of N C in 1987

[Linked Image from photos.smugmug.com]

It may have been slightly honed on L
The original bore R was 13 = .710 - .718 and at reproof was .710"
L was 13/1 = .719 - .728 and at reproof was .728"

3 TONS would be for a max. service pressure of about 9000 psi

Please check carefully for cracks at the apex of the R lockplate inlet.

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