Greetings....Cartridge Identification Help

[Vermonster]

Good morning, and Happy Thanksgiving! I am an avid hunter and am in law enforcement, but have never collected guns so to speak, just own a few of them. Anyway, I signed up looking for a little assistance with identifying what I believe is an old rifle round. I metal detect some as a hobby, and recently found 2 of these rounds, which nobody has been able to help with. The location is a place that was occupied from the 1880's to around 1910's or so. I have found tons (200+) of other rifle brass and shotgun headstamps from that time period, so I am pretty confident in that date.

In the first photo, they are in the center with the ????. You will see all the other things strung up as a reference. The shotgun shells to the left are all brass. The other photo is a size reference from the end view, one with a dime, the others with a .410 and a 20 gauge. It appears to be in between those sizes. By cartridge dimensions (51mm length, 17mm head, 15mm at base) (All rough due to being a little bent), it's around what I believe is a .577 size. It's a bit bigger than a couple 45-60 and 45-70 rounds I have found also. As for identification, the only mark I can find is in the last photo on the right. You will see it's a, "O" or a "0", not sure which.

Anyway, thanks for any help you may have, and again, Happy Thanksgiving!

[Thorax]

577 Snyder ?

[Vermonster]

That's the exact .577 we were thinking about, the dimensions are closest to that. I am just not sure because of no markings on it other than the "O". I know make of cartridge is probably a lot harder than caliber of weapon, but I was hoping that someone would recognize them.

If so, was that a very popular rifle here in CA in the late 1800's, or would that be considered to be owned by someone with a little more money?

[Thorax]

Hell, I'm not that old

I have no idea of the popularity of it.
try this on for size...
I have a .600 rimfire live cartridge that I have never been able to confirm anything about....but it's old, found it in California, and I still have it (somewhere).
It has a distinctive R-P headstamp (Remington peters) and even Remington had no idea it existed :/