just about all 209 primers are about the same except magnum 209's are hotter for magnum shotshells and theres no reason to use a magnum 209 in your muzzle loader if you want a to know which one is the lowest power 209 primer its the CCI 209 primer. All 209 primers are the same size because 209 means its a .209" dia. primer. So any 209 will work in a 209 primed muzzle loader but if you are looking for a low powered 209 the CCI 209 is your ticket. I dont think winchester would come come out with a lower powered primer...... because it would more then likely cause some confusion in the shotshell reloading world. I also know that some 410 loads use a magnum primer because a 410 uses a slow burning pistol powder that might need a little extra heat to ignite but most 410 loads use standard 209 primers. even if winchester made a 410 primer It wont be necissarily a lower powered primer but more likely a hotter primer.