How ever, more often than not, when they agree to measure and record 100 successively seated primers they are at a loss to explain the seating depth variations. This is opposed to the tolerance of plus or minus .002 inch recommended by several primer manufacturers. The ideal seating depth is .005 inch below flush for most primer brands. Only CCI suggests a differing depth, .001 lo .003 inch below flush with the case head. However, there is a better way to seat primers and that is by using a mechanical stop for the priming stroke.
Some tools are simply tighter than others.
Almost all of the various press-mounted priming units can be adjusted to take advantage of the mechanical stop in the press linkage. Of these, those that mount at the die station, often called ram prime units, have repeatedly provided the best test results with respect to uniform seating depths. Most reloaders find it relatively easy to maintain a .003 to .007-inch seating depth with these. I have carefully chosen several presses for prime-only operations leaving the ram prime units in place full time. I have one press set up for small pistol and small rifle and a second for large rifle primers.