No one has said anything after 68 reads, but I feel compelled to say that I think you are risking eyes, fingers and a Krag. Military blanks are often made from cartridge cases that failed some sort of acceptance test as a component of service ammo.  The list of accidents (?) small and some large with duplex loads of smokeless powder is quite long.

FWIW, cartridges for launching rifle grenades often use 5 grains of FFFg black powder as an igniting charge.