Groove around the mouth

[CEshooter]

Does anyone recognize these rings around these cases, just below the mouth? If so, what would cause something like this? The groove isn't a uniform distance from the edge of the case and there is enough difference there that I can feel it with my fingernail.

 

[spife7980]

From factory ammo? Have any more unfired you could check?
My first suspicion is a crimp.

 

[bpd459]

Factory loaded ammo, factory crimp.

 

[CEshooter]

It's factory Winchester head stamped .243 Winchester ammo but I can only find 4 pieces out of my bucket of spent brass that has the ring. The other pieces of Winchester brass don't have it.

Thanks for the info.