grouping?

[16Bore]

Take a butter knife and hold 3" of the blade on the edge of your kitchen counter as tight as you can. Now thump it.

Now lighten pressure a bit and keep doing it. You'll notice the sound (frequency) changes. As you continue to lighten pressure, you'll hear the tip of the knife tapping the counter.

Now imagine the edge of the counter is your action lug and the tip of the knife blade is the ass end of the action. Handle is the barrel.

Sure, you could argue that the velocity deviation of the load causes vertical (easy to see and hear shooting 22LR at 200 yards) but I've never seen a rifle that didn't shoot better after bedding.

 

[N2TRKYS]

Maybe a bedding job will fix the OP's original flyer issue. I've had vertical stringing while in load development in my rifles, none are bedded, that went away when a different powder charge was used.