The 16 in a circle means it was proofed with a !6 ga. 65mm( 2 1/2-2 9/16" chamber), the 16/1 is the bore diameter ahead of the chamber (this translates to 16.99mm), as expressed in gauge measurement. The crown U is the mark for the View Proof, which is a detailed inspection, including verification of measurements, after firing the proof load. The Crown S means it was proofed for the use of shot. The crown W means the shot barrel is choked, but the amount of constriction is not known (usually pretty tight). It was already stated that the rifle barrel was proofed with a 16 gram bullet. The St.MG means that bullet had a steel jacket. The crown G on the rifle barrel means it was proofed for a single projectile(bullet). There was a class of rifle cartridges that were provided in various case lengths that had cases near enough the size of 410 cartridges that metal 410 mases are sometimes used to handload them. Also, 410 shells are often fired in these rifles because the owners tried different shells/cartridges until they found something that would fit into the chamber. I believe it would be worth your time to have someone examine it closely to determine if it has been converted or if it was only marked as a 410 by mistake. You should see if you can tell if there are any other numbers ahead of the 3/26, if so they would represent the bore (not groove or bullet) diameter. In 1928 the bore diameter would be shown in mm and if there is a fraction a , instead of a . would separate the numbers. Fluss Stahl means fluid steel and Guss Stahl means cast steel, there is not much difference.
Last edited by Der Ami; 07/18/23 06:03 PM.