I was testing loads for my wife 6.5x55 Ruger MK II the other day and got high pressure signs with under max Nosler book loads. The powders tested were H1000, RL-22 and H4831SC. The other component were Nosler Brass, 140g Nosler PT and WLR primers. I only shot one round from each load because I was getting over book velocity for that load, but lower than max velocity according to the book and ejector marks on the cases. This has never happened before. One primer appears to have leaked and one was almost pierced. At least it looked that way. Bolt lift seemed fine. I pulled the bullets and reweighted the powder and in all loads it was correct. Wondering what could be the cause?
I thought of too short of throat: Nope plenty long and well over what they were loaded.
Improper head spacing maybe that allowed the brass to slam back into the bolt, but again not a problem before. However this was new brass, but a brand I have used before.
Bad primers maybe, but again that higher velocity with a shorter barrel.
I thought my scale was off, but used the same scale right after these were loaded to load .257 Roberts that were spot on velocity and no pressure signs.
Any ideas would be helpful.
