As for the largest cartridge it can be chambered for. I designed it for 30-06 sized cases, but since it requires a rimmed case, it will need to be a rimmed version in the medium bore family.

I did some research regarding the specific strength of the action. The dimensions critical to this are the action side walls, barrel band and corresponding barrel shank dia. The side walls are .2" thick, but can be left thicker if requested. ( the action is 1.25" thick)That's the same side wall thickness as a Ruger no.1, but my action has a couple of advantages over the no 1. First is the material. The No 1 is from a casting, and has releived areas where the sidewalls are thinner. I am using 4140 and 8620, and the cavity is wire cut on my EDM. The EDM produces a smooth, stress free cut. The breech block, also EDM cut is a precise fit, which reduces "hammering" from a not so perfect fit.

The barrel hole on the action is .875", which keeps .2" barrel wall thickness, plus the thickness of the barrel band around the chamber ( .164"). So, the dimensions of the barrel band and barrel shank require the case diameter to be .471" and smaller at the base, The rimm size should be .531" and smaller. This includes the 9.3x74r. So, to answer the question on the largest caliber, the 9.3X74R would be it.