A few things you may not have known:

[Bucky]

32. I agree that "shot of whiskey" etymology sounds mighty dubious. But...

The price of buying cartridges by the thousand is going to be significantly lower than the average retail cost you'd get from your local gunsmith or general store. If a glass of whiskey was two bits, but the price fell after the railroads increased supply. Then the conversion scale of one .45 shell to a shot glass of hooch could easily be equivalent, basically in the 10-15 cents range.

That said, there are etymology theories that run back to the 1700s.

The most likely origin for the word (and unfortunately the most boring) is found deep in Old English. In Nathan Bailey’s 1721 compendium, An Universal Etymological English Dictionary, Bailey says “shot” referred to “a Flagon which the Host gives to his Guest if they drink above a Shilling.” A similar note in Bailey’s dictionary for “ale-shot” indicates “a Reckoning or Part to be paid at an ale house,” aka a tab for drinking all that ale. About 300 years of etymological evolution can explain the shrinking of those shots down to a single gulp and the disappearance of the “reckoning” sense of the word.

So Anglo-Saxons were shooting their ale, their descendants were doing so from shots, and generations later, drinkers all over the world are doing shots of Fireball between games of beer pong. History really is a beautiful thing.