You have a rubberized grip on a suede sandbag, what did you think was going to happen? Note the up & right stringing?

Note - in my first response in this thread, I mentioned a "rider" under the rear of your grip.

What you have pictured is a guarantee to lift the muzzle. Grip's gonna grab that bag and not move anywhere, might as well be bouncing off of concrete. Give it a way to move, it'll move, and you'll be able to feel your way to a tighter group.

I shot from a pack, or even from X-bags when I started with specialty pistols (before you were born), and eventually came to realize what really works best, compared to what seemed to work better for the couple dozen or hundred rounds I thought meant something.

These aren't mine (I wish), but this is what the big boys use when they get their specialty pistols out to really do some precision work. They know a he11 of a lot more about making short barrels shoot straight than you or I.