In his "Pet Loads" book (collected reloading articles), Ken Waters wrote about loading the Krag cartridge and rifle.  He said something like "There is no reason to try for every last fps.  These are old rifles not suited for our modern loads".  Just because the cartridge case has the capacity and some of the loading manuals say that you can develop hotter loads does not mean that it is a good idea.

It is easier today to crack a bolt lug than it was in 1899.  I've done it.  A new jar of 4350 is cheaper than a replacement bolt body. 40.0 grains is a safe load.