You are picking nits. One or two grains will not make a (noticable) difference with bp.
However, if you want to get perzactly the measure you desire make yourself a measure. They are easy to make from many materials. One of the easiest is to use a length of copper tubing, squish one end in a vice, drill a hole in the squished part for a thong if you wish, pour in the exact amount of powder you are after, mark the top, hacksaw the tube to that length, double check to make sure it is what you want and you are set for life. BTW, the copper darkens and takes on an 'old looking' patina very quickly. I have one I made and have used for thirty years. No one has ever pointed to it and said "that ain't authentic".
