Hi Tinker & 3DogMike -

I'll try to provide more information and answer your questions.

Regarding the firing position, I was at a bench, shooting off a Caldwell bag (not a lead sled). Left hand under the forearm, but NOT grasping hard or pulling in. (Similar to this bag: https://www.amazon.com/Caldwell-Deadshot-Construction-Resistance-Shooting/dp/B000PG7VRO)

Regarding the bore, I confess I don't have great confidence in my measurements, but I came up with 0.504 land and perhaps 0.508 groove. Bullets measured 0.502-0.503 and were just lubed, not paper patched (yet). They had a gas check. Cast. 370 grain. I do not have a sizer.

Charge was measured by volume. Compressed 1/8-1/4" inch when seating projectile. Standard rifle primers. After pouring, I tapped the case a few times to settle the charge before seating bullet on top of a cardboard wad cut by hand (so rough).

Lube was ancient Thompson Center lube from 30 years ago when I hunted with a flintlock, spread in the bullets grooves and also under the bullet. Rounds were fired 24 hours after loading.

Brass was new Hornady.

Results were much better for left barrel, with all 3 striking no more than 2.5" from centerline point of aim. First shot was low 2", left 1.5". 2nd was low 1/2", left 1/2", 3rd was high 2.25", left 2".

Right were all further out from POA, at outside ring (6") spaced starting at 2pm up thru 1pm.

I'll get a picture up later. I am a decent shot and I knew while shooting this that I could do better (I was a bit nervous and excited.)

I will double check my volume measure for the charge before repeating.

Chris