Al primers must be seated to the bottom of the pocket. If not, the force of the pin's thrust must seat the primer fully before ignition can take place. This can absorb energy that is needed to fire the primer.
: Make certain the primer is bottom'd out.
: Remove the bolt, turn the shroud so the bolt is 'fired' and measure the protrusion of the pin. It should be not less than .050". If it is, it needs to be replaced.
: Military and other older actions that have seen a lot of use and blown primers and have had their pins smoothed off once or twice to prevent piercing, may end up a bit short.
: The only 'fix' for htis is a new pin.
: I prefer a 22# to 26# spring on my Mauser actions that see use in the hunting field and normally use 24# on my target '98 actions. Some people don't like them that heavy, complaining of too much action 'jar' but I've never had any difficulty, even with the match (position) rifles.