Greener577,
Your nice Sauer was proofed in Feb. 1930(2/30), so it could very well be a GI bring back from WW2. The 12 in a circle means it has a standard, for the time, 12ga chamber. The chambers will likely be around 2 5/8"( often called 2 1/2"), instead of todays standard of 2 3/4". The 13/1 is the bore diameter ahead of the chambers, expressed in gauge measurement. This works out to be about 18.26mm. The crown S means it was proofed for shot. The crown W means the barrels are choked, but the amount of constriction is not shown. The crown U is the mark for a View Proof, which is a detailed inspection after undergoing definitive proof, including verifying dimensions. The "Nitro" in block letters means it was nitro proofed in Suhl, but since Sauer was located in Suhl this would be expected anyway.
Mike
Thank you for the information. It seems to be full choke in both barrels. As far as 2 1/2” vs 2 3/4” chambers does that mean I should only shoot 1oz loads out of it? I will get the chambers measured to be sure.
Greener577,
I suggest you do measure the chambers, it could have been rechambered since the war and not marked. After that, what you do is entirely up to you. Some shoot them with proper length shells( they can be found on the internet), some shoot them with 2 3/4" shells, and some lengthen the chambers. Whichever you do, someone will argue with you, but it is your gun.
