ML primers are not as hot as shotgun 209 primers. 777 and Pyro need ignition that is generally hotter than percussion caps, but do not need ignition as hot as standard shotgun 209 primners. BH209 needs hotter ignition, and recommends standard shotgun 209 primers
Yea, I keep getting that backwards. I remembered that BH209 needs regular and 777 needs ML primers but I got the reasons backwards.