If you have the CVA Blackhorn breech plug do you still need to use a magnum 209 primer or can you get by with the regular 209 primer. I know the winchester 777 primers will not be hot enough.
I have been using Blackhorn and non-magnum standard Winchester 209 primers for a very long time. I have never had a single hang fire with 90 grains and 250 sabot out of a CVA Accurra w/Blackhorn breech plug. If OP wants to search and pay more, that's fine, but they've never been needed IME.
I also don't take any special precautions with my primers other than keeping them in a zip loc baggy. Hell they like to fall out of the platic square holders and I handle them with my bare hands to put them back in the boxes. No issues.
I also don't do anything special with my rifle other than avoiding bringing it in from the cold into a warm house. I've left it loaded from the previous season until the following and its never misfired after sitting for loaded for 8 or 9 months.
My recommendation is that the OP buys what he can find, shoot them, and draw his own conclusions. I wouldn't wait around looking for a miracle magnum primer as if the others won't get the job done.
I’ve used the muzzleloader primers during summer target practice with no problems but use CCI or Winchester for hunting late season to avoid any issues.
I have used win 209’s with no issue provided I foul with a primer or two first. If not the first shot is a misfire. i think this is due to oil fouling from cleaning.