The Beretta Vandalia- only about 300 were made. It was a beautiful single barrel gun, one came up for sale a few years ago and that was the first I saw since I saw them for sale new at the Grand in Vandalia, OH.
That was quite the strange one. The outward appearance of a Beretta SO, with a sidelock on one side and a sideplate on the other. However, it had the Purdy double underbite lockup.
I suspect it wass subcontracted out to/from another company, much the way the SO9 was to Famars, it wouldn't have made much sense to engineer, design, and manufacture parts which interchanged with nothing else they've ever produced to make a run of 300 guns, unless they'd originally planned to do a much larger run but stopped after 300. But I would have expected to see whatever the parent gun was at some point, the closest I can think of was the old Stoeger Zephyr.
