It's a large bore RF casing that was "played" with. It appears to be quite a common thing to do back in that era, when boredom set in around camp. Rimfire calibers up into the .50 caliber size were common in the 1860's...and many of those calibers were loaded for along time after they became considered obsolete because of the quantity of guns out there in working order. 44 Rimfire (think Henry rifle) was loaded all the way into the 1920's by the big manufacturer's...just a point made about dating locations where rimfires are found. That particular casing is too short to be a Spencer, I believe, but definately appears 50 cal. I will try and remember to dig out dimensions of the 2 different Spencer chamberings (both 50 cal, but different length casings if I recall correctly), and some of the other 50 calibers.
I observe here in AZ that I can rely on the casings to pretty accurately date campsites, based on the idea that this region was considered very hostile up into the early 1900's, so people armed themselves with the "latest and greatest." So if i find a bunch of large bore rimfires, I'm confident it dates to 1860's to early 1870's...when centerfire primers became more widespread. Even after "rimfire" died out in bigger calibers, "inside" priming and Benet priming confuses the issue on dates.
I have posted pics before of some unusual casings that were played with...smaller caliber casings pushed/pounded inside larger ones, and have found MANY 1860's era casings here in AZ that are cut into pieces, have holes drilled through, made into little "ornaments", even initials scratched on them.
