12 hours ago, Norm Matthews said:
I read that in the 1880's in Tombstone, an individual serving of booze cost the same as a bullet and bartenders would accept a bullet from poor cowboys for a small glass. That is how it came to be called a shot of whiskey. It is possibly how getting a shot came to be called "buying a round"
Amusing tale, bu sadly, a myth. The expression 'shot' meaning a portion of booze was in use 200 years before then. A 'round of drinks' is even earlier.