Today, Drachm is an apothecary weight of 60gr.

Due to the loads, ie: 1, 1 1/4, 1 3/5 - Colt was using the dram weight of 27.5gr., not the apothecary's weight of 60gr. per drachm.

In the mid 1800's, it appears both English and Americans were interjecting dracham and dram as being the same measurement in their writings.

This is evident with James Forsyth's book 'The Sporting Rifle and it's Projectiles, printed in 1862/3, where he talks of rifle loads in a 14 bore rifle not having
any great recoil with up to 5 drachms. Now, in a 14 bore rifle, 5x27.3 = 136.5gr. and yes, that is not great recoil in a 9 1/2 pound rifle, however 5 x 60 =
300gr. DOES. I've shot that and it lifted me up off the log chunk I was sitting on. Had my feet not been back to the rear of the log, it would have knocked
me over. I was expecting only the recoil of 6 drams (165gr.) mu hunting load, however, with talking, I had double charged the rifle with 330gr.2F.