Last night at the range one of the shooters picked up what he thought was a .30 cal. Carbine casing on the floor.
He showed it to me because he knows I shoot .30 Carbine and thought I might want it but it looked a little different. So I pulled out one of my .30 Carbine cartridges and held it up next to the one he found, and sure enough the case on the one he found was about 1/4" to 5/16" longer and the fired case would not quite slide over the .30 cal bullet so maybe it was 7mm -.284 or maybe even 6.5mm- .263 but I doubt it.
The case head was slightly different also in the shape of the extractor grove, kind of like a semi-rimmed case I would guess. The head stamp didn't give me any clues either.
I looked in all of my books but was unable to identify it.
Anyone care to guess what cartridge it could be?

Pic?  Even from a potato.

300 blk?

Well I've been researching all afternoon and so far the 7.62X38mm Nagant is the only thing that comes close.
But why wouldn't a fired case go over a 30 cal. (.308 ) bullet?
I wish I had kept the case and brought it home with me, now I just have to guess.
The case head stamping did look like some kind of old military type letters and numbers.