Years ago Creighton Audette wrote a detailed analysis with testing of rifle primer performance in Precision Shooting. As I recall he discussed magnum primers quite a bit and the problems often experienced with them. He often used the term " Brisance " when evaluating these hotter mag primers and how too much Brisance ( the shock wave that preceeds the full energy of explosives ) can actually shatter powder kernels. In so doing uniformity of burn is negatively affected resulting in significant velocity spreads and sub-optimal accuracy. I recall some of his photos that revealed the ignition spark and flame and how most magnum primers ejected much more flame than standard or benchrest primers. It's a really great series of articles written by a shooter with a true scientific mind. I believe it may be found sleuthing the internet

Rick

I know for a fact from guy that used to show up at a club range I belonged to that a large rifle mag primer by itself will push a bullet way down a barrel. What I don't know is the measurement of the lead bullet or barrel specs. That stunt always got me thinking about ' something ? ' . He was not the safest guy to be around when he had his testing beanie on or in the next lane station as he was continually experimenting and challenging ballistic rules. I really don't believe it was just coincidence that his face and neck was peppered with little black spots. 

Same club once held a candle shoot in the indoor range where with primers alone you tried to blow out a candle. It was fun but you needed to hold very accurately offhand. The history of this event apparently dated back to the Civil War I'm told. 

Rick