Recently noticed that their develops a ring midway on the shoulder about 1mm below the base of the neck. Any of the experts know what causes this and if there is a remedy? Thanks

Could be signs of case separation. How many times has this brass been reloaded? are you full length resizing?

Does your barrel perchance have a rifled insert? roger

Its a 5yr old CZ550 and Im using locally manufactured PMP factory ammo. I only reload for my .375 because from the word go Ive been getting sterling accuracy from the PMP ammo.

A photo of a fired brass would be useful to give an advice.

Try cleaning the chamber out with a chamber mop and see if there's a reamer mark in the shoulder where it's leaving the ring on the brass.

I cant get a good pic. I'm beginning to wonder if its not maybe brass flow? It looks to me like its very slightly raised.