Thank you for the nice report Tom.
As I believe I've made clear many times in this forum, adaquate bearing length, strong bearing surface and bullet fit to the gun of interest are the keys to getting top accuracy. For these reasons, it isn't often possible to learn the true potential of a gun by purchasing commercially cast bullets, even of LBT design. They MUST fit your own gun.
If you lit the burlap rest you must have been resting the barrel on it, not your wrist, which I've found best for printing small groups. When resting this way, put all the pressure you like on the bag while sorting out loads, but when a load is found and you want to set the sights for field use, lay just enough pressure on the bag to take the wobble out. This way, the gun will jump exactly as if you were holding freehand, and if it's possible or necessary to take a rest for a long shot in the field, your sights are on for it, so long as you rest the barrel lightly.