I just got back from the range again. This time I installed the power stem breech plug to see if I could duplicate my earlier success with it. First three 3-shot groups were similar to my earlier "Frustrating" range outing...two close one flyer.

I decided to tighten both the front lug, and rear lug bolt to see if that would make a difference. My next two groups are as follows:

Knight LRH
Group #1
Barnes 250 MZ with Harvester E-Z sabots
89.1 grains of Triple 7 fffg powder (weighed)
Power stem breech plug...using the T7 primer
Average velocity 2058 fps
0.912" c-t-c (two shots @ 0.335)

Group #2
Barnes 250 MZ with Harvester E-Z sabots
89.1 grains of Triple 7 fffg powder (weighed)
Power stem breech plug...using the T7 primer
Average velocity 2066 fps
0.767" c-t-c

The crud ring wasn't an issue using the power stem. I ran slightly damp Windex patches a couple times in the barrel after every shot, per SL'ers advice. Barrel fouling was much less with the power stem compared to the non plastic breech plug.

I hope tighting both bolts finally solved my "flyer" problem.