Howdy, Pards,
I have NOT shot .44 "Extra Long Russian" (that's .44 Magnum loaded to CAS specs), but can give you some guideline data on case capacities. Checking .44 Magnum brass (Remington) against Winchester .44-40 brass, I find the Maggie brass to have a WATER capacity about 12.5 percent LESS than the .44-40, when loaded with the same bullets (213.5 gr). IF MODERN .44-40 brass will handle 35 grains of FFFg, this would suggest a powder charge of 30.6 gr. of FFFg in the .44 Magnum case. Obviously, different brass brands, bullet weights, powders, etc., will cause this to vary.