The first attempt at shooting my handloads created some flattened primers. One rifle saw the flattened primers at one grain under max according to the most recent Nosler guide (none at lower charges). The other rifle had flattened and lightly cratered primers at max load according to the Speer Manual (none at lower charges).
According to the Nosler Manual, flattened primers can be an indication that the resizing die was improperly adjusted and has changed the shoulder position of the case, causing excessive headspace and therefore causing case stretching, telescoping the primer and giving it a flattened surface.
If that were the case, shouldn't the flattened primers have been seen after all charges?
Both rifles are in very good condition, and therefore I didn't expect excessive pressure since I didn't exceed max loads. The cases were new, and I did "partial resizing" using the procedure in the Nosler Guide (left about 1/16-inch between the die and shellholder). Case mouths did not come from the factory very round.
Velocities were lower than the guides (100 -200 fps) at all charges and were not consistent. Accuracy was not bad however. No signs of ejector marks and no problems opening actions after shooting.
A poor pictures is attached....What would be your guess, excessive pressure or poor sizing?