Primers:
It is well known that different primers deliver different energy levels. The way each company manufacturers and formulates the chemical composition, and configures the hardware (metallic) parts of the primer, all plays a major role in how the primer will deliver the energy to the powder.
Again, we must emphasize that it’s all about the particular combination, and whether a change in primer will show a difference in ballistics.
Shotgun primers are very sensitive to firing pin energy. This is due to the proportionally large displacement/deformation that must take place when the primer’s cup is crushed.
It is extremely difficult to pin the data down to a standard one load, where primer X will always deliver higher performances than Primer Z. AAC developed our loads using a standard typical primer. If all conditions are the same, the difference between primers will rarely be dangerous. It is obvious that if the load one is using, are already running at the maximum level with primer X, it would be unwise to merely change the primer and continue loading. This is also true for any change in component or procedure.
Once any component or procedure is changed, the combination will react differently. The proper way to proceed is to reduce the load by about 0.5grain to 0.7grains, and then confirm the performance by measuring the velocity or sensing the recoil/flight time. The reloader can then adjust back to the same velocity/recoil level, by increasing or decreasing the charge mass, or by adjusting to a stiffer softer wad or decreasing or increasing the crimp.