I have used a mk85 since they first came out. I started out with number 11 percussion caps,then to musket caps, then to using their 209 conversion kit. Now I'm back to musket caps since I can only use t7 in it and not blackhorn.I have never heard of what you are talking about unless its the thing I saw on the precision bullet website about using 25 cal primers in some set up. for hunting i much perfer musket caps with my triple 7. they are much much easier then putting one of those plastic inserts with the primer on the nipple in a rushed hunting situation for a second shot.rws musket caps work great and i have never had a misfire.