Larry, I don't know if you saw my "bore" post on UJ, but that's what whdtt told me. The bore on the Belgian guild I just picked up is about .711. If one does the math equally dividing between .729 for a 12 and .667 for a 16, I came up with exactly a "13 ga."
In your opinion, you think I should have a smith check the thickness and maybe lengthen the cones to say 1 1/4".

Or do you think to leave it as is and use RST loads. Would 2 1/2" be better in this case to use or 2 3/4"? It has 2 3/4 chambers.

Don't sacrifice the future on the altar of today