Yoda - The line you're talking about is where the solid case head meets the thin wall of the case. LE chambers are oversize, so the thin case expands in dia to meet it. What your seeing is the junction where the two different diameters meet.
Often you will find that the line is only on part of the case. This is due to the extractor pushing the case to one side of the chamber. Of course, after a few firings, the line is more fully established.
Regarding headspace - you're better off partially resizing the case with your FL die. This will give you longer brass life, and you dont need to change your bolt head.
Often you will find that the line is only on part of the case. This is due to the extractor pushing the case to one side of the chamber. Of course, after a few firings, the line is more fully established.
Regarding headspace - you're better off partially resizing the case with your FL die. This will give you longer brass life, and you dont need to change your bolt head.