The English used 2 3/4" and 3" 16 bores at that time too. Usually if the gun does not have chamber length markings it will be 2 1/2". Don't be tempted to lengthen the chambers and thereby weaken the gun as I'm sure you can find the right ammunition if it is 2 1/2". One thing you may find with German guns of that period is that they had a sharp chamber cone; more or less a dead stop rather than a taper, as they were primarily intended for paper case roll crimped cartridges that opened dead to the start of the end of the chamber. Might be worth having a gunsmith who is familiar with European guns take a look at it and advise. Lagopus.....
