05-09-2014, 06:13 PM
I'm not seeing spirals, I see rings. Some of those rings are parallel, and some are skewed, giving the appearance of spirals. Here is the scenario I propose, the bullet is picking up marks at a very slight angle from impacting against the entry to the bore, this combined with too many loading cycles, is working the bullet around in the case to change the angle.
Waiting for an AR in .45-70 with a 30 inch octagon barrel, case hardened receiver, and extra fancy walnut furniture. Until the day someone makes one, I guess 6.5mm Grendel will do nicely.