Nope, this is correct. Amazing what has been lost to time, at least by those of us who think we know something. But given the confusion it must have caused, maybe best forgotten.

INSTRUCTIONS TO YOUNG SPORTSMEN

by Peter Hawker 1826

"put one drachm and a half of powder, exclusive of priming,to an ounce and a half of shot.....(the powder I have measured by apothecaries weight the shot by avoirdupois)".
pages 105-106