Daryl,
I have tried Longshot and it shows a lot of promise. Same Winchester components as the original post but used 32 grains of Longshot. This load is shown in the Hodgdon website for 1 1/8 oz of shot giving a velocity of 1420 fps.
I'm just running out of time before deer season begins to do more testing.
I did try blackpowder loads, 120 grains of Swiss 3F with card/fiber wads and the inverted gas seal under the ball. In a gun that weighs less than 7 pounds the recoil is quite noticeable.