What wildcat?

[WestKentucky]

30-30 case cut right at the shoulder without reform has a ID of .401 which would be tight enough to use a standard crimp on a 10mm bullet. 1.97” of hollow brass case at what would average out to be about a .410 cylinder. .26 cubic inches of case capacity converts to somewhere in the neighborhood of 65gr H2O. Would be quite potent with a slow pistol powder or a fast rifle powder.

I know it’s been done, because everything has been done. But what is it?

 

[WestKentucky]

And chambering would be about as simple as running a 30-30 reamer into a 10mm barrel and then cleaning it up after going just barely deep enough to allow for a rim cut.

 

[troy fairweather]

Only thing I can think that's close is a 40-50 sharps straight. But it's based off the 303 brit size case. Seems most 40s that size used a 303 or 30-40 case.

 

[tightgroup tiger]

.401 Herter's Power Mag. It was also made from 30-30 brass at one time. I think it's already been done.
http://castboolits.gunloads.com/showthread.php?322689-401-Herter-s-PowerMag-Brass