Most of the loading data I've looked at for the Krag round put 150-165 gr. weight bullets mighty close to .308 Winchester ballistics. I like to load my 1898 Krag carbine with 220 Hornady's and 'about' 41 gr. IMR 4350, which pretty much duplicates the original 220 gr. cupro-nickel fmj military load giving it 2100 fps out of my 1899 Krag rifle. The 220 round noses also shoot a LOT better than other bullets, mostly, I suppose, because of the long bearing surface that performs well in less than perfect bores. I've used that bullet in some mighty nasty looking 1903 Springfields at about the same velocity, and even they'll turn in some impressive targets. Recoil doesn't seem to be as sharp with the heavies, and are more pleasant to shoot than the lighter slugs.
Having two Krag rifles, I think I'd have to pass on the idea of punching out a .30-30 Handi, and leave it as-is. I load Dad's Topper with 165's using 170 gr. data, and they work just fine. Gotta watch out, though, as most bullets in that weight range made up as spitzer soft points perform best at a bit more velocity than the .30-30 will deliver downrange, so the shots are still limited (self-imposed) to 'around' 200 yards.
Oh, one other thing to consider....you'll likely find a box of .30-30 on the shelf in the gas station at Resume Speed, Wyoming, and the .30-40 might be a bit more problematic if you leave your loads sitting on the counter and don't realize it till you're halfway to the stomping grounds!
