I do not have a 30-40 Krag but I do shoot reduced loads from my .303 British and 30-30 Winchester.
Below is what I shoot for a reduced load and for fire-forming my .303 cases and the idea came from the Speer manual for the 30-40 Krag with their 100 grain plinkers.
I would like to make a suggestion for just two bullets for both of your rifles, the .308 100 grain Speer Plinker and the Hornady .308 170 flat point made for the 30-30.
You can use the 100 grain plinkers for both rifles for practice and fire-forming cases. And the 170 grain flat point for higher pressure hunting loads or full house practice.
I loaded the 170 grain flat point in my 1943 03-A3 30-06 and used it for hunting eastern white tail deer in the woods. I did this for two reasons, the large and long military chamber on the 03-A3 was very hard on cartridge cases when loaded to higher pressures and would stretch and deform my 30-06 cases. The second reason was the Hornady bullets are "interlocked" and will not separate or loose their lead core.
The 170 grain Hornady bullet was designed for 30-30 velocities and if you load it in your 30-40 Krag you will have a bullet when loaded over 2,400 fps that stops deer in their tracks. The 170 grain Hornady or any 30-30 bullet has a softer lead core than 180 grain .308 bullets designed for much higher pressure and velocities of 30 caliber rifles.
Also you can keep the pressures down in your 30-40 with this bullet and save wear and tear on your rifle with lower pressure loadings.
You will need two more powders, Trail Boss for your reduced loads and IMR-4895 which can be loaded to below minimum loading data and is very versatile when loading any rifle.