Offhand, sitting, and bench rest shooting

It is interesting how my vertical accuracy improves as I move from offhand (red) => sitting (yellow / legs crossed with elbows rested on my legs) => bench rest (green / front sandbag).  10 rounds were fired in each position.  This is with my Savage Mk II 22LR bolt action rifle.

As for the horizontal skew in my bench rest shooting, I think this is due to the way my sand bag grips the rifle...it is an 'H' shaped rest, and if there is torque against the rifle, I think it causes movement when I fire the rifle...I am going to try a tube type sand bag that doesn't grip the rifle from the sides, and see if that improves things.

(Follow up 6/18/2011...turns out the sandbag isn't the issue, it's me!  Once I place the rifle in the sandbag, I need to rock the rifle left and right a few times to settle things to center...once I do that, the horizontal skew tightens right up!  I tried using a block of wood with a towel on it to rest the rifle, and I'm far less steady and accurate than I am with the 'H' bag rest.)