First 500 shots were with 13.4. I foud more flyers than with 8.44 grain.Try the JSB Exact Monster 13.4 Cylindrical.
The magic is in the Vulcan 3.Good heavens. I would have liked to have seen the look on your face after you got done shooting the second group. You must have the gun set at the magic speed. My dads BSA will do pretty good out past 50 with 8.44’s at 830fps but I don’t know if it can match that.