Semi - what kind of primers were you using? I always thought that a 209 primer was a 209 primer. Until I got to reading about them playing with them. I've been using the 209s made for MLs lately with improved accuracy. Maybe a fluke but that's how its been coming out.
From what I've read, the theory behind them is that they are not as hot as a regular 209 primer which some say makes the bullet 'jump' off the main charge before it is ignited. This may be causing the flyers. But it may be worth a try.