caribsteve
Really no specific reason, maybe other than length. I just about used a Winchester T7 primer because I was shooting the T7 first - but then decided to go with the Winchester w209 because it is the coolest regular 209 primer that I have and I am not a fan of the mag primers.
Plus over time we have found that hot primers are not needed with the Lehigh conversion - especially the vent liner portion of the plug...