I purchased a complete upper from AR15 Performance and my 6.8 bolt was always very tight in the carrier in fact if gently brought to battery with the charging handle, it would not fully lock fprward in the lugs unless the forward assist was pressed.. Trying to rotate the bolt in the carrier by hand was difficult, and I was blaming it on the gas rings being too tight. They would not freely rotate with the bolt removed. I replaced the rings and they now rotate freely but that did not fix the problem. After firing 20 rounds with a couple failures to feed, I noticed shiny worn spots through the black phosphate finish of the extractor. Upon closer inspection I found that the rear of the extractor is extending beyond the body of the bolt, binding on the inside of the carrier under extractor spring pressure, and causing the tightness. As a test and in order to isolate the problem either to the extractor or bolt, I temporarily tried a 223 extractor which looked and measured identical to the 6.8 and it also extended beyond the bolt body and was tight when inserted into the carrier. It seems that the extractor pin hole in the bolt itself was drilled out of spec.
Has anyone experienced this?
Here are some annoteted pictures. For comparison, one picture is of my 50 Beowulf bolt which is trouble free.