Bur in chamber?

[K22]

I had the same problem with a Weatherby Vanguard. My gunsmith professionally polished the chamber for a nominal charge and the problem went away.

 

[232]

Unless Cooper has made a change, they used a reamer designed for Remington221 brass.

Before lapua came out with their 221 brass there were several variations of reamers.
Main difference was in the neck diameter. .232 was the most common reamer neck
diameter settled on for no turn necks when using Remington 221 brass.

When lapua 221 brass came out, the necks were thicker, and also the diameter at .200 from the base was larger. A newest bestest reamer came out for 20vt fans using lapua brass.

Neck diameter in some reamer prints went to .2355 for lapua brass with no neck turning.
Diameter at the .200 base line went from .374 for Rem221 brass to .3783 on prints I
have seen to accomodate lapua FAT brass and to AVOID the CLICK.

Lapua is not producing .221 brass now, and it remains to be seen if the bean counters
will put it back into producton.

Ironic?

I know the above probably has nothing to with your scratches, but it more than likely explains the CLICK you are experiencing. You might try removing the ejector and slowing down your bolt opening and see if the scratches remain.

 

[Fotheringill]

Until I saw the picture, it sounded like ejector marks. Then, I looked.

I would send the picture to Cooper first.