What caliber/calibers were the rifles referred to by the buffalo hunters needle guns?
Did that term refer to the action or cartridge?

From True West History of the American Frontier

A European invention, the needle gun got a lot of use (and publicity) during the Franco-Prussian War of 1870-71. The name comes from the firing pin, long and slender like a needle. It pierced clear through the paper-encased cartridge to strike the primer. The .51 caliber gun was the father of all modern bolt-action rifles.

Americans made a few needle guns too, but these were soon replaced by rifles that fired metallic cartridges.

Thanks MickinColo for your input. That’s about what Dr. Google had shared with me also. I’ve been reading Zane Grey’s Thundering Herd and one of the hunters preferred the needle gun as opposed to the big 50. Some had the Creedmoor sharps but reserved those mainly for injuns.
The fellow using one actually killed a fellow with it and the ones investigating were able to tell he’d been killed by the needle gun. Since it was 50 caliber also it makes you wonder how they did that.

One of my shooting buddies plays with a French Chassepot needle gun. Rather interesting rifle. Sorry, no pics of the gun but here's a pic of the cartridge. (A dud he bestowed on me. Such a guy!)




Something on the order of 70 gr. powder, 385 gr. bullet. Bullet body is .450 diameter, driving/base band is .465. You can see in the second pic where the "needle" pierced the back of the cartridge on the way to hitting the cap which lies behind the bullet. All the paper is either consumed or blown out the barrel upon discharge, leaving the chamber clean for the next shot.

The rifle is quite accurate, when it actually fires.

The answers here do address guns which were properly called “needle guns”, but given the context of what you read they’re more likely referring to the 50/70 trapdoor which also was referred to by that as a nickname due to the long needle like firing pin.

This!

Anteloper nailed it, the common term of the day for trapdoors was needle gun

What anteloper said is what I have always heard.

So I have a couple needle guns and didn't know it.

Prussia put the hurt on Austria and France with their "Dreyse needle gun". It is mentioned many times in various histories about German unification and, biographies on Otto von Bismark mention it as well. Bismark was the Prussian Chancellor at the time of unification and held mostly responsible for the unification of German city states, duchies and 'kingdoms' into the nation we think of as Germany today. I have several such histories in my library This is what I always knew as a 'needle gun' until a few years ago when somewhere I read about Wm. F. Cody and his 'needle gun', Lucretia Borgia', which as best I remember was a 50-70 Trapdoor. And I hope my memory hasn't failed me.

https://en.wikipedia.org/wiki/Dreyse_needle_gun