lever locking scope base - grouping issue

[novanryder]

I shot my 6.5 Grendel for the first time today at Chabot and I had a Leupold 4.5-14x40 VX-III on it, and zeroed it in at 50 yards but had to stop. It seems that the groups I was getting were inconsistent and sometimes jumped by about an inch or two on the paper. Usually 3 shot group within .5" ... jump... another of the same an inch down or up... and it kept doing that. Really weird. I have the scope secured in an American Defense Recon-X cammed scope base with 1" rings. I adjusted the screws for the cams till you could just barely get the scope off the rail when you opened the levers, which is obviously how's it's supposed to be cuz you're supposed to be able to take the damn thing off quickly with the cams. I was usually the Alexander Arms 6.5 Grendel Nosler Ballistic Tips @ 120gr. Has anyone experienced this with a cammed scope base? Should I just lock the sucker down tight as hell despite the cams?

[1lostinspace]

no don't tighten them, maybe it's the scope base of the rifle not the scope mount.

[Rust]

Yeah I've been fighting the same problem with my rifle. I think Ive narrowed it down to a bur left on the rail in the machining process but I have not had time to get back to the range yet.
I'm shooting a Sabre upper in 6.5 with a GG&G riser holding a IOR scope in Seekins rings. unfortunately the 35mm tube needs both rings and a riser since there are no one piece units on the market to my knowledge. Ammo has been Alexander arms 123 lapua scenars and Black hills 123 SMKs. My groups would hit one round on target, one high right two inches, back on target, high right 2 inches, back on target... So I would be shooting two distinct groups about 1moa 2 inches apart.
As I shot it more it started to settle down a little and close the gap between groups. I've tried pulling the scope on and off repeatedly to wear the rails in a little and It started to show a bright spot where it was making heavier contact. I found a small bur and raised spot there which I cut back flush, but don't know if it cured it.
I think that GG&G using a one piece clamping bar allows any small imperfection like that or even a bit of grit that may wind up stuck to the rail on install to mess up the whole works. If its riding a high spot it probably just rocks back and for like a seesaw with each shot. I think that a two point clamp would work better, at least in my case. Hopefully cleaning up the milling will have cured my problems though.

[maxicon]

It's possible the scope is shifting internally - it can happen even to good scopes. If you have another one you can try, that'll isolate it.