Thread: Primer question

Originally Posted by zimmer

Primer pockets like the cases themselves (well USA ones) are governed by SAAMI specs ie a maximum and a minimum value provided for primer pocket depths for manufacturers to work to. Primers vary between brands in over all length. Maybe even between batches. You could have a primer pocket at the deepest end of the SAAMI spec (still within spec) and a primer that is shortish. Outcome if seating flush is the bottom of the primer may not be correctly in contact with the bottom of the primer pocket which can lead to erraric ignition or no ignition.

I'd have to rechech SAAMI but I think these are the specs/tolerances -
Large Rifle PP specs 125 thou to 132 thou.
Large Rifle Primer specs 123 thou to 136 thou
So a 123 thou primer seated in a 132 thou pocket, flush, will not be a good combination.

The other thing that happens is if you uniform your primer pockets with for example a Sinclair tool, which is non adjustable, you may cut your pockets too deep. I had that happen with a Sinclair tool which before I realised it was cutting my pockets to 132 thou whereas I wanted 128 thou. IIRC 132 thou is still within SAAMI spec or right on it. They refunded me for that tool.

I have always believed that to be the most important objective of seating primers ( i.e. seating to the bottom of the cup ), for certain and consistent ignition. To me, secondary and almost as important is to have primers flush with or just under the case head surface. Just so if cartridges are moving under recoil in the magazine there is no chance of the primer being contacted by any surface or projection.