This is the second vena contracta I have had, and they are both Ferlach guns. This one is an Anton Sodia sidelock with 16 gauge chambers and bores that are hard to measure, but seem to taper from 16 to 20 gauge with an abrupt tightening to about .570 (!) at the muzzles.
My questions are:
Has anyone shot/hunted with one of these?
What was the purpose/theory behind them?
Why would they show up in Ferlach in the 1920's?

Here's an interesting group of tests on the 12-20, 12-18, 12-16, 12 choked, and 12 cylinder. Note, it appears the most open patterns started with the 12-20 and worked their way tighter as the constriction from 12 was more open.

http://books.google.com/books?id=inQCAAA...0gun&f=true

From Vintage British Shotguns: A Shooting Sportsman Guide, by Terry Wieland:




OWD

Daryl - thanks, those are interesting tables.
OWD - that's funny! I was wondering about recoil. But I believe the reference above is to Britain in the 1890's...any idea about these guns popping up in southern Austria 30 years later?

In 1897 Webley built Vena-Contractor sidelock guns for Joseph Lang .