RE: Bad Pioneer powder or primers?
The same thing happened to me with the APP sticks. Burning sticks flying out the barrel like tracers and landing 20 to 30 yards downrange.
I switched to Pinnacle FFFG loose and haven't had the same issues. I like it much better and it is very clean.
From what I hear the old APP pellets were OK when they were shaped like cylindars if you kept them dry. A patent infringment forced them into the stick configuration. I will never use the stick shape again.