Sent the Encore to TC. The TC technician found a 'flap' of metal on the crown and fixed it. He got about 1.5 minutes with Winchester factory ammo at 50 yds. Turnaround time was about a week from my door till it was back! He said the action would close on a 0.005 feeler and not release it. I'm still wondering about that because I see primers backing out enough to see or feel easily and I DON'T think I measured wrong when it would accept a 0.011 feeler and still close but...
Back again after testing more loads:
Got considerably better accuracy with some old Nosler 52-gr. solid base match bullets & AA-1680 in neck-sized cases.
Used the starting load and about 1/2-way from that to the max in my manual.
Varied seating depth from the maximum [determined by chambering a split-neck case and bullet] in approx 0.005 steps down to about a 0.035" jump to the rifling.
Saw some evidence in group size and chrono results that it likes a 0.010-0.020 jump better than kissing the rifling.
Several groups were around an inch and a couple around 1/2-inch. So, there's progress.
Thanks, all, for your comments.