My guess is that the hook on the extractor isn't sufficient to hold on to the case rim. It's a relatively easy fix (if you have a spare).
How difficult is it to remove a spent case from the chamber when this happens? Is it lodged in tightly, or does it come out with relative ease?
Do you (or a friend) have another working Grendel that you could borrow a bolt from (or just the extractor if there's a headspace issue with an alternate bolt) to test in the new uppers?
How difficult is it to remove a spent case from the chamber when this happens? Is it lodged in tightly, or does it come out with relative ease?
Do you (or a friend) have another working Grendel that you could borrow a bolt from (or just the extractor if there's a headspace issue with an alternate bolt) to test in the new uppers?
Drifter