When choosing a primer seat the seating depth must be determined which is how far the primer is inserted into the case. If the primer is seated too deep below flush internal components can be damaged which causes inconsistent ignition and misfires.On the other hand seating too high which would be above the flush prevents rotation of cylinders in revolvers. For semiautomatics it can create problems when the bolt slams. Because this is so important only the best product should be purchased which is why reloaders depend on the MEC Primer Seat.