7mm STW - Stuck cases, at wits end
I've got a 7mm STW, actually it's my buddies, that the cases stick after being fired. The bolt lift is fine, not stiff at all, with the bolt completly up we have to tap the case out with a cleaning rod. Last Saturday at the range we tested 7 different loads, 180 Berger VLD .010 off the lands, Federal 215M primer, 73 - 76 grains Retumbo in .5 grain increments. Everything was shot over a chronograph to verify velocities. At times the stuck case seems completely random. The load with 74 grains stuck, the load with 76 grains did not. After the case is tapped out of the chamber you can see an very obvious mark in front of the belt where the case rubbed against the chamber. We have checked and double checked the headspace, replaced the bolt handle to ensure primary extraction and replaced the extractor.
Any ideas what is wrong with rifle? Could the chamber be rough or out of round?