I have 2 rifles chambered in 30 US. Gas checked Lyman 311291s work well in both rifles.

311284 bullet was designed for the 30 US/Krag
it is about 215 grains, round nose, gas check. A good shooting bullet in most 30 cals. The original Krags were in 10 twist, but I expect your 12 twist should work OK.

OTOH, that suggestion for the 311291 is Very Good. It is one of the easiest 30 cal bullets to get good accuracy, Nom
170 grains. for plinking you could use it w/o the gas check
over a light load of Unique or similar
beltfed/arnie
beltfed/arnie

I have a Krag action I rebarreled with a 1:12 twist 0.308” Douglas barrel and chambered in .30-40.  I use 21 gr of 4759, behind a gas-checked cast bullet.

Generally, I find any bullet between 165-200 gr works well, but if you’re only going to get one mould, the longer the bullet the better.  Even with the 12” twist.  If you want to go for range, you will need a gas-check design.

For some weird reason, my rifle shoots best with the bullets sized to 0.308”.  Don’t know if this is a “Douglas thing” or what.  With the bullets and powder charges weighed, and crimp-on gas checks, the shots land with surprising frequency on the Ram silhouettes at 500M.  They will drill through 1/4” aluminum plate at that distance with no trouble whatsoever.

For sighting I use a ~2-1/2x Thompson-Center muzzleloader scope, mounted ahead of the action, Scout-Rifle style.  That and the trigger limit the percentage of hits, IMO, more than the gun and load do.

Don't forget 311403 or a similar design.  Shoot as cast, do not size.  Pan lube.  Just put half the base band in the mouth of the case.  Light load of 4227 or something close.