Can your app calculate the impact of different primers or primer sizes, i.e. standard vs. magnum primers?

To our knowledge, no one has so far fully understood and verified the impact of a specific primer on the ballistic KPIs of a load, such as maximum pressure, powder burn, and muzzle velocity. We have also done many tests, but have not been able to determine a reliable formula to allow primer definition as input for a ballistic calculation. The understanding to date and reasons are as follows:

•  The general rule of thumb is that magnum primers ignite the powder faster, which usually (but not always) leads to higher pressures with the same powder charge.
• Results already vary between primer brands of identical size (i.e., large rifle primers from two different brands). Therefore, calculations would need to be based not only on size but on the specific primer product (size & brand).
• The influence of magnum vs. standard primers depends on several factors: e.g., powder position in the case/fill rate, shape and size of the powder grains, powder temperature.
• The impact of switching between primers and primer sizes seems insignificant for most powder and calibers (+/.- 5-7% pressure variation). 
• Magnum primers achieve better consistency in ignition and, therefore, better accuracy for magnum calibers with large powder charges.

This is why we haven't included the primer (size) as an input variable to the calculator, and suggest you leave sufficient safety buffer vs. the maximum allowed pressure.