6x45

[StoneHendge]

WIth the vertical stringing, recoil moves the rifle backwards and in the absence of the ability to move backward, it follows the least past of resistance which is the stock rolling up the shoulder. If the bullet is still in the barrel as it rolls upwards......
My guess is that that is what’s going on, but I don’t use lead sleds. Maybe make sure the stock is firmly against the rear of the sled before you set your shoulder. I would also keep your non shooting hand off the rifle

Gas tube should not be touching barrel nut.

I haven’t found good variance to always coincide with accuracy. I’ve gotten the same ridiculous variances with AR Comp in Grendel that other folks get here, but never got it shoot better than 3/4 MOA in my 22” JP (which is capable of 3/8).

We’ll see about that velocity. If it wasn’t CO’s worst year for snowfall in the history of the universe, I’d probably have a Lab Radar by now.