GEHA Mauser and common European shotgun calibres question

I got a GEHA Mauser because of its interesting post WWI history
And here is my question…
12g GEHA is chambered in 2 9/16” inch shell. It was made largely for export, some for USA. It was a hunting/sporting gun. Nowadays, at least in US, most shotguns appear to be in 2¾, which is longer and more powerful. I have no idea what chambers present day European shotguns. So, it would appear that the length of a shotshell increased from 1920’s to present day, probably both in US and Europe. Why? Did the deer and bear grow bigger and stronger? Or skeet regulations changed?

Perhaps for wildfowl usage the need grew for the longer shell. It’s been said that at least 4 pellets need to hit a bird for an effective kill. Not sure about the that, but It’s been said.

I don’t know if there is a hard fast date on the adoption of a particular shotgun shell length in any given country. Original Model 1887 Winchester shotguns were chambered for a shorter 12 gauge, 2 5/8 inch, I think. The Model 1897 Winchester shotgun was chambered in the now standard 2 3/4 inch twelve gauge.

in the story you link to it is said that Gustav Genschow company due to partly Jewish ownership was taken over by Gustloff. That is nonsense. Long before Nazis came to power, Dynamit AG bought the majority of shares. Karl Genschow continued to manage the company.

There’s a lot in the linked article I’m doubtful about, but I am certain that the Geha shotguns weren’t built from converted rifles. They were assembled from new parts, never before used, intended for Spandau’s rifle production, which ceased in late 1917 while these components were still in the pipeline. Some were used by the Reichswehr in the 1920s, others were sold off as in this case. Jack