Chambers that are 2 1/2” or 65mm long, for a 28 gauge, are a bit of a problem on older European guns, at least here, in the US. That is a fairly uncommon loading here.
I’m looking at the wall thickness at the breech end, and, it seems quite substantial. The gun might have an action more properly sized for a 20 gauge gun, with 28 gauge barrels mated to that. If that is the case, it would explain two things, the comment that they aren’t made like that today, and the gunsmith not being worried about using 2 3/4” ammunition in it.
Good luck.
Best,
Ted
