if the gun is really old you should look for proofmarks
The proof marks for the Beretta single shot, I've posted in my penultimate post. It is a 1946 design. It was made in '54. From what I've worked out this evening, the Model 412 was an entry level 16g. Looks very nice, though...
The VC 12g is more recent, probably from the 60's. I'll see what I can see on it.
I'll also have a look for any number codes for the ammo, although all the information should be on the link I post earlier...
Hopefully, this will lead to the answers, and these guns can be shot for the first time in about 30 years!!
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