Shooting BP in my flinter is by volume. When loading into cartridges its by weight. Remeber that the amount of bang you get for a charge depends on what powder your using and it's grain size (FF vs FFF). My .50 loves 70 gr of FFF but to get the same POI using FF I need to up it to 80. The FF is larger grains and burns slower then the FFF. When using real BP a good place to start with a rifle is to use the volume equal to the caliber and go from there. I found my .25 flint shoots ok with 25 grains but great at 30. Take the time at the range to see what yours likes...that is half the fun.
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