A image of the underside of the tubeset might garner a date range. It is an eccentric breech but I believe Central-Feuer/Fire and just a paper hull cartridge, which may be similar to the below:


>>
Advert showing Collath 1 gauge & 4 gauge in his gauge scheme.


Lancaster's contribution from NE

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=107196&an=&page=&vc=1




Proofmarks from previous page & note the 1 gauge stamp, which I assume to be a 12 bore? Also looks to have the same tubeset knitter initials.

0 = 10 gauge
1 = 12 gauge
3 = 14 gauge
4 = 16 gauge
5 = 18 gauge
6 = 20 gauge
7 = 24 gauge
8 = 28 gauge<<


https://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=193971&page=all

Cheers,

Raimey
rse