I'm happy that so many of you like the Winchester primers - but the reality is that
all major brands work fine. In 35 years of reloading and over 25,000 rounds reloaded (using CCI, Federal, RP, and WW primers) I've had only two true misfires that I could not account for. To have a 1% failure rate tells me that the poster is doing something wrong.
The idea about tumbling media blocking the flash hole makes sense if the poster used it. The "moisture" comment is puzzling as most reloaded rounds are very waterproof - to get enough water into a case to trigger a misfire with water extruding from the case is hard to envision. It is possible that the primers were damaged when seated, by too much pressure, off-center seating, etc.
I just cannot blame the primer brand, particularly since it happened with what I personally know to be an outstanding primer, the F215. This one has a tough metal cup, and a weak firing pin strike could account for the misfires. But that doesn't explain it happening in two different rifles......
PS - why is the poster even using F215s in the .220 Swift? Speer is the only current data I've seen recommending magnum primers, and the milder CCI-250s at that.