Thread: Sooty Necks

What causes sooty necks on the cases?

I thought it was something to do with not enough pressure sealing the neck in the chamber on firing?

I did a ladder test the other day and the necks were all quite dirty after firing. Some of the loads were over book max as I had found no pressure in the previous ladder test.
On the last load I had a bit of trouble opening the bolt and had a flat'ish primer, so know thats over loaded for me. But it was still sooty.
Powder is AR2217 in a 270wsm.

Thoughts...