Thank you for the input folks, I was leaning towards 4064, I will definitely be trying that now.
Rich
IMR4064 has a couple of advantages in this application. It is bulkier than ball powders and small kernel extruded powders like Varget and RL15, so the case will still be relatively full even if you're backing off the throttle a bit for your 99. It's ignition and burning characteristics are also better suited to lower pressure operation than some newer powders, so this may aid consistency in the development of your 99 loads.
