So the question is where and for what shooting? Target, large game, small game..., as laws vary from state to state.
For example here in Maryland IF you want to shoot for deer with a .40..., and not all states allow this..., then you'd need 60 grains (of 3Fg) to start, as that's the law for a deer load.
On the other hand, if it's targets and small game, then 60 grains is going to be rather "stout". Another way is to start with grains equal to caliber, which would be 40 grains of powder with your patched ball. That might also be a bit heavy; you'll have to try it. Some folks will use 20-25 grains for small game and punching paper.
I like 30 grains when I go small critter hunting here in Maryland
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I then simply double the powder from my 30 grain charger and thus have my 60 grain load when I go for deer.
LD