Forster Products offers two methods for this important handloading step:
SAFETY – Seat primers with a slow, steady pressure to avoid breaking the primer pellets or setting off the primer. Avoid any sudden or sharp blow when working with primers. Wear safety glasses and hearing protection when reloading, and always position yourself such that you will not be injured in case of an accidental explosion. To dissipate pressures, the primer tube is open. This opening should be turned away from you.
Both primer solutions are engineered with such precision that no excessive tolerance or “slop” is required in any of the mating parts.