First.....look at the load data from a reliable source. They should have the primer brand and type listed in the recipe. Make sure the data is from a reliable source....not from a guy with a tagline of "BIGBOOM" who is on a forum.
Standard primers: Sufficient energy to reliably ignite the powder charge in the case.
Magnum primers: More energy than standard and are usually recommended for cartridges that contain a large quantity of powder such as the 45-70. (Not always the case as it depends upon the powder and recipe....back to reliable data)
Benchrest Primers: Primer makers (as I understand it) weigh each primer. For benchrest primers there is a much tighter tolerance of low\high weight so that loads can be more consistent than other primers.
Some powders, such as Vithavouri state to NEVER use a magnum primer with their powders.
Last edited by Steeltrap; 02-24-2019 at 02:34 PM.
Reason: Add Vithavouri comment