'RichWIS' - gave a good suggestion about using a .308 Winchester F.L. Sizing Die to Neck-Size .30-40 Brass.

Keith - confirmed your fired Brass is dimensionally typical for 'once fired Krag brass'.

The .30-40 Case Neck is quite long. It is not necessary to Re-size the entire case-neck, especially if reloading 130 to 165 grain bullets. With lighter projectiles, you may have to seat bullets Out, as far as practical, to have your reloads feed through the Krag action.

I am not a 'Precision Bench Rest Shooter' (BR does not appeal to me). I am a Military Match shooter. I have gotten good results from my Krags using Standard Dies, Neck-Sizing, using 'starting loads' of IMR-3031 & IMR-4895 with 180 grain and lighter jacketed spitzer projectiles (to keep pressures low), and standard large rifle primers (Winchester).

The .30-40 U.S. Army has been around a long time and is fun, accurate and easy to reload. There is a wealth of Data on this cartridge.