I have had the same frustration. You move a scope and think... that has to do it, only to find the POI moved maybe an inch or two.
That is a great 100 yards target. I almost purchased on of those rifles when they were being near given away by stores. But decided I did not need one. I always liked the looks of them and the concept of them.
So that just grease and a breech plug fixed the primer problems? With all primers? How is the trigger on that rifle?