As has been said, the .30 US is not a hard round to load. And if ever a bottleneck case was made for cast bullets, it's this one.
There are those who will say the Krag will not feed Spitzers. This is flat wrong. The Krag will not feed SHORT spitzers. If the OAL is within spec, the shape of the nose means next to nothing. Flat, pointed, round, hollow point, the Krag will eat them all, as long as OAL is maintained.
For a military load that shoots to the sights, the search begins and ends with IMR 4350. 40 grains under a 220 Jacketed RN duplicates the pressures, velocity's, and numbers on the rim of the original. As good a target or open sight hunting load as you will find for any Krag. Lighter bullets can be used, and other powders, but this is the one if you want to know what Teddy Roosevelts shoulder felt like.
For close in steel plate shooting, any lead bullet 180 or more grains is fine, over a 3/4 case of Trail Boss. Set the sight between 4 and 6 and you'll be right on target from 100 yds in. See the Trail Boss KISS topic above.
Krags can vary in bore dimensions, Mine are both just under .309. But they can go larger, though I've yet to slug one over .310. Not saying they're not out there though. Check yours and plan accordingly. Mostly I think its 100 years of wear. My M1898 Infantry is pretty much worn out, so I've got a brand new CMP Krag barrel waiting to go into it one of these days. These barrels are a great deal IMHO, and any worn out Krag can be transformed by one.
https://estore.thecmp.org/?cat=BAR