I would measure the diameter of the chamber, end to end, with a micrometer and the length with a machinist's scale, and send that info to RMC. After fireforming, the brass would conform to the chamber well enough for shotgun work. I have an eight gauge that has rather deep rim recesses, much deeper than commercial eight gauge shells. One firing with standard eight gauge shells and they are good for a lifetime of reloading. That is, the lifetime of the paper empties.