77gr. SMK Bulletts inconsistant lot to lot
I loaded 100 rds of Sierra 77gr SMK with 23.3gr of Varget. I always seat 5 rounds a little long. I then dial my seating die down to 2.260 on the longest of the five. The average COAL of cartridges loaded from the first box of 50 is 2.255. The COAL length of cartridges loaded with the second box of 50 is about 2.480. I used a bullet comparator and they are all exactly the same. My concern is high initial case pressure. Being that the average case is significantly less than 2.260 do you think I will have a pressure problem on ignition?
I'm using a Forster Comp. Micro seating die
I will be shooting these from a magazine
If the comparator length is identical, then each bullet is seated the same depth into the cases.
I would have reset the seater for the new box in order to seat the bullets out to 2.26 inches. Sierra uses different machines and operators, and sometimes the dies are changed, so there is no expectation that the bullets from lot to lot are the same.
Seating deeper into bottleneck cases reduces internal volume of a case so little that the effect is negligible, and the increased jump to the rifling often reduces the chamber pressure.
the second box of 50 is about 2.480.