Perplexed....need your thoughts

[Bulldogce]

Ive got a 280AI built on a Winchester 70 by Accurate Ordnance. AO mounted the NF rail, Leupold Mark 4 rings, and Vortex AMG scope as part of the build. I zeroed the rifle with Nosler factory 140gr loads and hunted with it all last season. It was submoa but not by much. I shot and confirmed zero 30 or so days ago.

2 weeks ago I loaded up two 10 round ladder tests with Nosler brass and 162 Amaxs. I shot these over a magnetospeed with no target downrange just gathering data looking for a node. Found a node and loaded up 10 to shoot for a accuracy check.

Couldnt even hit the target! Figured out it was shooting 12" low at 100yds...3.1 mils...kinda freaked me out, thought I screwed up the load. Went back yeaterday with factory ammo and shot three rounds and it shot 11" low....seeming to confirm that the zero had changed. Came home and checked rorque on all the mounting screws...all within spec and solid.

So I'm perplexed. Did the mount shift (seems unlikely) or is the scope the problem?
Would you rezero and see if the problem persists, swap the scopes and confim its not the rifle.....I kinda hate wasting ammo trying to chase the problem so Im looking for ideas or procedures to help identify the problem.

 

[dzander]

I can't imagine a load at 100 yards would change POI by 11", thats a lot. I'd swap the scope out if it was me.

 

[BuildingConceptsllc]

No way the load had anything that drastic at 100 yrs. If you checked the mount, it's the scope. I'd definitely re-zero and see if it persist before replacing the scope, only to rule out you or someone else accidentally turning turrets. If the scope has a zero stop set then you probably need a new one but hopefully that one has a warranty.

 

[Bulldogce]

No way the load had anything that drastic at 100 yrs. If you checked the mount, it's the scope. I'd definitely re-zero and see if it persist before replacing the scope, only to rule out you or someone else accidentally turning turrets. If the scope has a zero stop set then you probably need a new one but hopefully that one has a warranty.

It has locking turrets with a zero stop. It couldnt be an errant twist....

 

[dzander]

Leupold should repair it if it's bad at their expense.

 

[Dthomas3523]

Take everything apart and re-torque. Zero rifle.

Take dead blow hammer or your palm and beat on it a bit. The rifle and optic. Nothing rough. Just simulate bumping around while driving and such.

Check zero. If zero is still good, run the turrets up and down a while. Then check zero. If zero off, it’s then scope. If zero is still good, then put it in safe and check it periodically.

If zero changes after slapping it around, put another optic on it and repeat. If it happens again with another optic, it’s something in the torque/mounts. If it doesn’t happen again, it’s the optic.

I’m assuming the rifle is bedded?

 

[Bulldogce]

Yes, its fully bedded with free floated barrel in a Manners stock by AO. I checked torque on action screws as well , they are within spec.

 

[ma smith]

run a basic ballistics calculator on your ammo/speed at 100yds, and see what kind of fps variation lines up with your data....if the results are not plausible, then you eliminate that as a variable...and starting figuring what's wrong with your optic/etc.

 

[Dthomas3523]

run a basic ballistics calculator on your ammo/speed at 100yds, and see what kind of fps variation lines up with your data....if the results are not plausible, then you eliminate that as a variable...and starting figuring what's wrong with your optic/etc.

3.1 mils would take a variation the isn’t really possible. (Unless he went from around 2900fps and is now making subsonic ammo).

 

[BuildingConceptsllc]

It has locking turrets with a zero stop. It couldnt be an errant twist....

Think I'd call manufacturer then and see what they could do for you. If you checked all the tightness specs, that really only leaves one option.

 

[Jack Master]

Take everything apart and re-torque. Zero rifle.

Take dead blow hammer or your palm and beat on it a bit. The rifle and optic. Nothing rough. Just simulate bumping around while driving and such.

Check zero. If zero is still good, run the turrets up and down a while. Then check zero. If zero off, it’s then scope. If zero is still good, then put it in safe and check it periodically.

If zero changes after slapping it around, put another optic on it and repeat. If it happens again with another optic, it’s something in the torque/mounts. If it doesn’t happen again, it’s the optic.

I’m assuming the rifle is bedded?

This. Do this.

Then you need to put your brain in a place to trust your gear. If you don't trust it when you go re zero and test things you will never be confident with it. This lack of confidence in any gear can ruin great rifles and shooters. Reset the gear and trust ut until you find out it fails you again, which I doubt it will.

 

[Bulldogce]

This. Do this.

Then you need to put your brain in a place to trust your gear. If you don't trust it when you go re zero and test things you will never be confident with it. This lack of confidence in any gear can ruin great rifles and shooters. Reset the gear and trust ut until you find out it fails you again, which I doubt it will.

I think rezeroing and trying th deadblow hammer is a good idea. The hard part will be the second half....that is trusting it....that might take some mind bending. When you got a pile of money in a rig, with top shelf parts and craftsmanship, it should inspire confidence....

 

[Simonsza1]

Leupold should repair it if it's bad at their expense.

It’s not a leupold

 

[bax]

Agreeing with dthomas3523. Tear it down and start over.

Just suppose ... assuming a one-piece base, the front screws holding the base to the receiver got loose. The rear screws are still tight, but now there is a gap between the front base and the receiver. Point the scope at the target but the barrel is pointing lower. There are two big problems with this theory: that size of gap should be visible and if the base is loose, it should not group - so OP should see a gap, group low, and "group like shotgun". If the rear screws are still tight, maybe group not too bad ... ?

After that, I would guess "scope". Try a different scope.

If it turns out to be the base, consider bedding the scope base to the receiver, blue locktite on the screws, and tighten base screws to 15-17 inch-pounds.

 

[dzander]

I think rezeroing and trying th deadblow hammer is a good idea. The hard part will be the second half....that is trusting it....that might take some mind bending. When you got a pile of money in a rig, with top shelf parts and craftsmanship, it should inspire confidence....

It’s not a leupold

my mistake.

 

[Baron23]

Leupold should repair it

Vortex AMG scope

 

[dzander]

Did you ever figure out what was causing your problem?

 

[Bulldogce]

I took it all apart and retorqued it back down. Went to the range and rezeroed with factory ammo. Beat on it with the palm of my hand hard for a while....got some strange looks from the other guys on the line. It held zero....ran the turrets up and down several times....it came back to zero. Hopeful it is solved but I need to shoot it alot before im sure.

 

[918v]

Maybe you didn’t have the turret screws tight enough?

 

[sleeplz]

Ive done this with my amg a few times. You have to torque down the screws in the turret at a even pace from each other, ensuring your not screwing one side screw too tight before going to the next screw.

laslty, screw all the screws with more force so that you are sure the screws are holding zero and turrets move the reticle. Ive gone to matches with loose screws in the turret and it’s destroyed me.

 

[Marine52]

You said that AO had initially mounted the scope for you. This may have been the problem. If the scope rings are over-torqued then a binding can occur on the erector inside the scope. Your additional adjustments may have resulted in a sudden “unbinding” of the erector tube and account for the big shift in impact. Sounds like you got the torque right when you remounted the scope. I never let anyone mount my scopes. if you want it done right, do it yourself and with a good torque screwdriver.