Primer Seating Depth

Primer seating depth – how far the primer is inserted into the shell case – is carefully controlled in factory ammunition. You also need to be aware of primer seating depth when reloading. Seating the primer too deep below flush can damage the internal components, leading to misfires and inconsistent ignition. Seating the primer too high (above flush) can cause the cylinder to not rotate in revolvers, and can cause problems when the bolt slams home in semi-autos. Seating above flush can also result in misfires.

Unless you are reloading on a progressive machine (each pull of the handle yields a loaded cartridge), the primer seating depth is controlled by feel as the primer is inserted. This is especially true if you are using a handheld priming tool. The primer seating depth is best checked with your finger tip. Sliding the index finger across the bottom of the primed shell case will quickly determine if the primer is above or below flush.

The ideal seating depth is just below flush. As you gain experience in loading, the feel to accomplish this will become familiar. It is best to use your finger to test every primed shell case. If the primer is above flush it can be run through the seating operation again to push it below flush.