Using Magnum large pistol primers to ignite TrailBoss is a little like using gasoline instead of charcoal lighter to start you briquet's. Too much 'whoosh' for the job needed. Every loading manuel, magazine article, book, and personal direction I've every read or heard since starting to reload back in '76 stressed Mag primers to be used only for 'slow burning powders'. As Shotgun F stated, in his previous post, they "put more flame into the case". You don't need that with TrailBoss. It is rated a FAST burning powder and is ignited faster and burns faster. Using the Magnum primer will cause more pressure and spikes for the desired fps and pressure in the 45 Colt load you want for your SASS match. I've yet to see a TrailBoss load listed using Magnum primers. Check the manuels, saying this only for your and others safety and the gun you shoot with. If you have no use for the mag primers, try trading them for some standard ones with someone that needs them or just 'bite the bullet' and buy some standard ones.