Your beloved 180 gr bullet is the weight of 180 grains of barley taken from the center of the head. It takes 1.333 grains of wheat to equal 1 grain of barley. It's the only unit of weight consistant in both the troy and avoirdupois systems. It's pure coincidence that it's 1/7000 lb av but that does make it easier to estimate the number of loads you can get from a lb of powder.
