Blackpowder is very forgiving because the pressure/burn rate curve is much flatter than nitro. It is really difficult to overload a muzzle loader and I would imagine it is impossible to overload a cartridge. Although BPs do vary in performance the differences are not great enough to lead to safety concerns. Some will perform better than others but will do so safely. Excessively fine powders will actually burn slower because there are less spaces between granules to allow sparks to propagate. Go ahead and enjoy!
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