After reloading and shooting hundreds of rounds w/o a single misfire I've suddenly got a high occurrence of misfires while trying to help a friend develop a load. To date one of my pet loads (different brass and primer combo) hasn't misfired in his gun (likely a couple dozen rounds fired) so although I plan to pull apart his bolt and clean it out and dry lube it I don't feel that is the root cause. [Note mag primers are being used as that is what was on hand, loads were worked with them in mind, lets not hash out that selection aspect other than its relevance to a misfire or not.] My previous loads with WLRM's and both FC & RP brass haven't had a single hiccup in hundreds of rounds in my gun nor a couple dozen in his. He bought Hornady brass for his loads and I cracked into a box of 9.5Ms (again it was on hand, first time using them). We bagged a load ladder today as 3 out of 7 failed to failure to fire! Additionally I had loaded up a small ladder .5gr increments with a new (to me) bullet to determine a max charge using those same 9.5Ms for my gun (first time using them) in some WIN brass, 1 of 8 failed to fire. Primers were seated with a RCBS hand primer, I noted more resistance felt with the 9.5Ms vs WLRMs but nothing preventing a complete squeeze of the handle (I'm under the assumption the spring determines seating force in that tool but let me know if I'm unknowingly crushing them in doing what I'm doing, I'm doing the same thing I've always previously done w/o issue using the WLRMs). Right now it seems the 9.5Ms are generally at the center of the issue (be it the actual primers, or the primer/brass combo, or how I'm seating them). Right now my plan was to break down all those rounds leftover (as the 9.5M combo is unreliable for whatever reason) and run out and grab a fresh box of primers, likely WLR or 210s if they are around. If someone has a clue on what is going on here I'm open ears.