To be honest Chris it looks to me like an 'exploded' cartridge, as suggested by the other guys. I've found 303's, 30's and even 50cals like this. All tapering gone, splits on the rim.
PS Only way to be totally sure is via the headstamp which, unfortunately, looks long since corroded away.
Here the pictures .
Rim and primer ring look the same to me. If they are differnt got to be same maker thanks for the rim pics Chris.
I agree with zwerge, Eric and Steve- they look the same to me, save the one on the left having had some rather significant issues with its neck. I can see a horizontal shadow on it at the same point that is the base of the neck on the intact case, and the cracking where it'd be much narrower just supports the idea; compressed the way it is to form a neck, the metal's not just going to happily stretch back out again, but would more likely split.
Are the measurements other than the neck area the same? Base diameter, body diameter and overall length?
Ohhhhh- pillage then burn...
I have to agree as mentioned previously, it looks like a round thats detonated outside the breech. I can't see that old type of case having the power to discharge such a large round as what it looks like it should.
definately looks like a split cartridge as these guys have descrived the crack certainly explains the loss of shape at the bottleneck and as the guys have all said plenty of rounds cooked off or froze etc to supply this kind of finish
Thank you guys for all your input,Well now I know ,It is just a 8mm Lebel.