Alex,
I don't think anyone has made balloon head brass since WWII.
You can get more powder in the balloon headed stuff, but the cases are weaker and become unusable quicker. With the lower case capacity of modern brass, you should be able to reach the same pressure and velocity with the smaller amounts of powder than in the original loadings.
I know I get about the same velocity with 65 gr. of Elephant FFg as the original Frankfort Armory load of 70 gr. of FFg with a 405 gr. cast bullet in my .45-70.
Doc
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