Thread: 7mm rem magnum accuracy issue

Afternoon all. So my son has a Tikka 7mm rem magnum. Pretty much over short time it has gone from same hole almost groups to 1.5 inch groups , same ammunition he’s used all along. Ive given the rifle a good clean, retorqued scope rings , mounts and action( 35lb on action).
It runs an older gunworks suppressor. Scope is a Vx5.
I found in the chamber a small “lump” of what I think was carbon , right on the edge of the shoulder. Ive cleaned that out.
Would that cause the accuracy issue? Or is is something ive missed. Any thoughts appreciated before I start changing scopes .Cheers in advance .