Hello.  I have a Spencer (repeater) that has an octagon barrel and is a single shot.  I read that after the civil war a number of companies acquired Spencer rifles and converted them to meet the demand of buffalo hunters.  Since this is a new acquisition, I haven't determined the caliber and can find no company information on the barrel.  Can anyone help me?  Thanks.

Over the years I've seen quite a few Spencers converted by gunsmiths to sporting rifle confuguration. Perhaps one of most well known was Gemmer. I'm not aware of any company who did this on a large scale. The action design greatly limits cartridge length, so there are few options. The most common is .56-50. There was a post-war .56-46 spencer cartridge developed for sporting use. I've not heard of a single shot only version. Does yours not have a magazine? Please post clear, close up photos.

Steve

Years ago I ran across one of those sporterized Spencers with a heavy octagon barrel, forend with a pewter tip etc. The bore near the chamber was mangled, like somebody tried to run a big tap in the bore. I mentioned it to Dave Thorn and he went and bought it.
Before he got flustered and re-sold it we kicked around the idea of making it a single shot. As near as we could tell, it would be no big problem to run a 50/70 reamer in and that is all you would have do. I don't think the magazine and feed mechanism would interfere with single shot operation at all.

The original poster has not come back to update us on his chamber cast or anything else. Maybe he lost interest    

Certainly the Spencer action greatly limits the cartridge length. But oddly enough, my M1871 Springfield Spencer 2 band rifle takes a longer than normal .56-50 cartridge. The cartridge length it takes is the same as the .50-45 carbine cartridge.  I'm guessing Springfield Armory just used the .50-45 reamer when making these. But the rifle will not cycle with the standard .56-50 length cartridge either. Rather odd.

While not really considered a Buffalo cartridge, the .50-45 loaded with 45gr of Goex 2F and a 350gr bullet out of my Spencer gives a little over 1100fps.  That's no slouch.  Here are the two side by side.

Spencer was a very talented inventor and patented several single shot rifles, in addition to his repeater. 
The single shot rifle, shown in his patent of 1873, easily handles a 45-90 length cartridge but I don't think that any of these rifles survived the Army trials.
Otto

The Spencer could be used as a repeater or as a single shot with the Stabler Cut-Off Device. Edward M. Stabler of Maryland invented the Stabler Cut-Off Device. It prevented the cartridge from feeding the magazine to the receiver by limiting the lowering of the breech block. The carbine could then be used as a single shot weapon. A few of the carbines manufactured by the Spencer factory, plus 19,000 of the 30,496 of the Burnside Spencers were equipped with the Stabler Cut-Off Device.

Chipmaker: Thanks a lot. It would not have occured to me. I did use a central ( 6 o'clock extractor ) but with hot Hornet rounds I am finding extraction difficult. 

I am thinking of building a full size one now in 45-70 gov or 45-90. I have modeled it and it might be that the latter case is rather long for it, keeping to the proportions of the patent. 

Now that I have nearly recovered from my meltdown, I am spending time ( maybe too much ) in my workshop, but my priority is to finish the pending projects I have before I embark on new one

This Spencer action was in the 1872 trials results published in 1873 with the adoption of the trapdoor Springfield. Here is some pictures that they published. Note that the hammer is much shorter than in the Patent.