That's the basis of my opinion also, Dogjaw. I don't see how in the world a primer or any load is going to produce such a perfect flash hole. Why don't we see it more often?
Kayser - A point on the scorching you noticed. In general when you see scorching around a case after firing, it usually means the pressure was lower than it should have been, not higher. The case fails to expand enough to create a seal in the chamber and gases leak around it causing the burn marks. You'll see it all the time with "cowboy loads" in .45 Colt.