Thread: At a loss

So doing some shooting yesterday with my WSM and Im getting heavy bolt lift but no ejector marks.
Now this is a load I developed 2yrs ago during summer, its 3 grains under max for my rifle and all rounds chambered fine with no resistance.
I've pulled several rounds to check the powder charge and all are as it should be. The cases are tumbled before being full length sized and are on their 4th firing. I only use 1 brand/type of primers so no chance of a mix up there. Projectiles are all seated at correct COAL to be 10thou off.

I feel I've eliminated an issue with the ammo so now thinking rifle......

Would a carbon ring be a possible cause????