Some info in a thread on same last year:
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Well, if you mean what Sharps originally cut them I can't help. But I do have 2, both are Ballard repops, one a schuetzen and the other a 4-1/2. These are my thoughts.
Rim Dia; a case from Win 30/40 in hand is .535, an as-recieved Baco from R-P case is .544. Since rim dia is an air dimension anyway make sure it's big enough.
Rim thickness; the Baco cases I have are reworked by them to increase the rim thickness to original spec.s, I reface them to get a specific thickness for my chamber. This also lets me seat Lg pistol primers flush. Probably more work than most would want to fool around doing. I would decide what brass to use and that will dictate the rim.
Neck; If your chamber is the least bit snug and you are using a bullet seated very deep you will probably have to ream or turn any brass formed from 30/40 because the brass is tapering and the wall is getting thicker at this point. Otherwise they don't go all the way into the chamber. The neck will be bullet dia. + (wall thickness x 2) + whatever clearance you want. I would take the brass you intend to use, load some rounds however you intend to, then start measuring then get a reamer made. Conversely, if you already have a reamer available, you will have to just do what it takes to get the brass to work. 
Case Length; nominal is 1.875 
Other thoughts; Similar to 38/55 but with black powder the fouling is spread thinner due to more bore area. That is a theoritical plus. Little bit bigger hole will get you an extra point every so often. Little bit heavier bullet kicks a little more I suppose. Cases were a lot more fooling around the way I did them. Reloading dies are a LOT more money.
Wouldn't ever think of selling either one of mine.
kootne

I checked the chamber dimensions and fired cases and loaded rounds also. The chamber is .438 at the neck and it tapers to .457 at the rim. It does not appear to have a straight section. A loaded round in 303 brass has a .433 diameter neck. The fired brass measures .436-.437. 
Krag brass is .452 in front of the rim and 303 brass is .451. The brass thickness at the neck is .012 for the 303 and .010 for the Krag. That's why I use the 303 brass, it doesn't get reworked as much as the Krag.
I cut my chamber with a 40/70 SS reamer made for the .405 brass which is heavy brass. I use the reamer for the 40/50 SS and the 40/60 Maynard as well as the 40/70 SS.
I use the Lyman neck die to size the cases and I made a straight line seater with the same reamer designed after the Bonanza Bench Rest seater die. the Saeco 740 bullet over 42 grains of FFF Swiss was generally the load of choice to shoot in this gun.
My son holds several national records in BPCR silhouette shot with the round while he was a junior. He just missed making master class while still a junior.

You should be able to find the reamer drawing on the PTG website. If not, give them a call and they will e-mail you a copy as an attachment. Very accommodating folks.