Obscure, Obsolete, and no longer used calibers

I know. I'm a weapons nerd :) For more information on these might I suggest Ian McCollum's Forgotten Weapons https://www.forgottenweapons.com/
and Othias and Mae's C&Rsenal.
https://candrsenal.com/
Both are FAR more versed then I in this arcanum.

Trivia :
Question: What was the first US Military adoption of a percussion fire firearm?

Answer: In around 1838-39 the US Navy had outfitted a South Seas Expedition. For its use, they had ordered 150 Elgin Pattern Dagger Pistols (an early firearms fad based on the big knives used by famous knife fighters of the day like the recently late Jim Bowie; -the Alamo)