Gard,
I agree, the 32-40 is a great place to start. However, if you want options for light recoil and a round that will stay supersonic thru 200 yards there are two Stevens options that were top competitors in the early 1900's you may want to consider. Both straight tape cases.
28-30 Stevens 135 gr Hoch, 12 - 12.5 gr 4227, small rifle primer, 1,600 fps. Rocky Mtn Cartridges can turn brass for you from rod stock.
32-35 Stevens (308 cal groove) 150 - 165 gr bullets. With all of the 30 cal mold designs and options, the 30 cal option is worth looking into. Brass, Cody at Rocky Mtn Cartridges can also turn cases for you in this caliber.
For more info on these two options, see the attached link to a 1937 load manual, Sharpe. (pages 372 & 395)
I have a CPA in 28-30 and CPA 32-20. The 28-30 was much easier to dial in than the 32-20 CPA. Same extractor, two barrels for one CPA action.
(You need to Login or Register to view media files and links)