Good comments above for the reloader.
I've been loading for an original (un-sporterized) 1898 Krag for something like 40 years now. So here is what I've found.
Jacketed Bullets:
1. My Krag's bore measures almost .309." Krage bores can go from .308" to .310" and the throats are notoriously long for the original 220 grain military bullet.
2. Current 220 grain jacketed bullets taper much faster than the original projectiles making accuracy questionable.
3. In my rifle (with a very good bore), Sierra 220 grain RN bullets are inaccurate as they taper too fast and do not fill the throat. Hornady 220 grain RN bullets shoot very well and will often shoot 1 1/2 MOA.
4. With jacketed bullets, H4350 powder has produced the best ballistics and with 40 grains (imagine that) velocity equals the original velocity of 2,000 fps from a 29" barrel with an extreme spread of 29 and an SD of 11 for 6 shot strings. Accuracy with the Hornady 220 grain RN is excellent as noted in #3 above.
Cast Bullets:
1. I size the bullets to .310" or .311" and lube with Alox/Beeswax lubricant and a crimped on gas check. In addition, I use a separate neck expander and expand the internal neck diameter to .308" or I neck size with a 308 Winchester collet type die for a .308" internal diameter. The 308 Redding collet die sizes only half the neck and that works well and enhances good bullet entry into the bore due to a good case to chamber fit.
2. With the Lyman 311041 bullet (designed for the 30/30) of 170 grain, I use SR 4759 powder to achieve a velocity of 1,675 fps for 2 MOA accuracy. If loaded to a higher velocity, the accuracy goes south.
3. With Lyman 311334 bullet of 187 grains using SR 4759 powder to achieve 1,850 fps, accuracy is 1 3/4 MOA for 10 shot strings at 100 yards. This bullets keeps its accuracy at extended ranges due to its spitzer design. It's .300" nose riding design fills up the Krag's large throat well enough for good accuracy.
4. I seat the bullets to just barely fit length wise in the magazine in order to fill as much of the long throat as possible when the round is chambered.
5. For the absolute best accuracy with cast bullets in the Krag I use "Pufflon" filler over the powder which (depending of the load) will reduce group size by up to 40.%
I have found when shooting US Military rifles with a 1 in 10" twist (Krag, Springfield & M1 Garand) that 1,800 fps is the sweet spot for cast bullets due to their limited strength compared to jacketed bullets.
While I prefer SR 4759 powder (and have a good stock of it) I have also tried the 5744 powder. It also produced good accuracy and ballistics, but due to its high nitro glycerin content, the barrel heats up extremely fast. Heat is the enemy of long barrel life and original barrels are irreplaceable so consider that when choosing a powder.
I shoot at least 30 cast bullets for every jacketed bullet not only for their accuracy, but to preserve the life of the barrel.
187 grain cast bullet group and original Krag cartridges: