I am using dacron filler for the first time and need advise. I am loading 45-70 with 320 cast and A2400 [24gr] and a WLR primer. I already shot this load over a chrono and got some eratic results. So, I decided to use a dacron filler 1/2" thick cut approx. 5/8" square pushing it in the case with a pencil. The groups were more like a pattern at 100 yds. After I shot the initial bullets I had loaded I decided to up the charge 1 grain. What I noticed when I resized the cases was that the die met more resistance at the bottom 1/2" or so on the case. Leads me to believe the "powder detonation" with the filler occurred in the first 1/2" or so of the case. Maybe I am missing the obvious, did I do this wrong? Is the filler too much or packed to tight? Is this just normal occurrence with fillers? I sure would appreciate some advise.