Need some info, AR with scope all the way up hitting low

[Encoreman]

Ok guys here is the scoop. I have a flattop Bushmaster AR with a Burris. P.E.P.R. scope mount and a Tasco 6-24x40 scope. I haven't shot it in awhile so a friend and I took some long guns to the range. This gun shoots about 6 inches low with the scope screwed as far up as it will go. I checked the mount is tight everything looks good. This gun has not been fired in a few years, but it was pretty close last time I shot it. Any helpful info will be greatly appreciated. BTW .223 caliberThanks Mac

 

[greyling22]

Scope went bad?
Gravity surge?

Only scope I ever had that did that was an old vertex viper. Came from the factory shooting into the dirt. They replaced it with one that worked. I was a fan of vortex for a while because of that, but as I hear more and more stories like that, I realized that vortex just doesn't put out a very good scope and they rely on their warranty to make people happy with their inferior/poorly qc'd goods.

 

[LiveLife]

If AR shoots 6" low with vertical adjustment maxed out, something changed whether scope, mount or both.

I would take the scope and mount off and reinstall making sure everything is tight and see how it shoots. If you have another mount, try it. If it's the case of scope not keeping crosshairs, time to replace the scope.

If it still shoots low with vertical adjustment maxed out but consistently groups well at the same spot, you can consider shimming the scope mount.

 

[Encoreman]

I was hoping for a cheaper answer. LOL I have a couple of scopes I can mount on it and see if that is the problem. I have had the scope for about 15 years, but have never shot is a bunch. Maybe it is mad at me for keeping it locked up and not out on the range. Thanks Maac

 

[herrwalther]

Did the scope shoot accurately before you put it in storage? Sounds like just a bad or damaged scope to me.

 

[Hugger-4641]

Being a Tasco, it probably doesn't have the double spring system on the turret that Burris and other higher end scopes have. After checking all mounting screws as already suggested, Try running the turret back down 24 clicks, then tap on the turret lightly with a pocket knife or small wrench. See where the POI is now. I bet it has not moved much or maybe has come up a little. If so, then move the turret back up 3 or 4 clicks at a time and tapping on it each time and see what happens.

 

[wiscoaster]

Make sure the reticle is exactly horizontal and vertical when the rifle is level and aligned with the horizon. A canted reticle can make elevation and windage adjuments pointless. I've seen a couple instances where people were experiencing the same symptoms the OP described and it turned out the scope wasn't properly levelled. Don't know how that could go bad just over time, though ....

 

[Encoreman]

Thanks for all the ideas. I took mount off of gun and re-attached and checked scope to mount screws and they were tight. Tomorrow is pistol shooting day, so it will be a couple of days before I can shoot it again. Hugger that sounds like something to try. This should serve as a warning to all, every couple of months at the max we all need to take out our long guns if only to shoot 3-5 rounds to verify zero. I won't think of taking any of my hunting rifles out on a hunt without checking them a few weeks before season starts. I will try to update if and when I find the problem. Mac

 

[Skylerbone]

With an AR it’s fairly easy to get a bore sight. I simply remove my upper, pull the bolt, and set the rifle in my cleaning vise. Then a quick alignment with the neighbor’s chimney about 27 yards away while sighting down the barrel. Once I get it locked in, I adjust the windage and elevation to match.

If your reticle fails to move, it’s time for a new scope.

 

[BigBL87]

As others have said, my guess would be scope or mount is the issue.

Not an AR, but I have a Weatherby Vanguard that was shooting 8 inches low at 50 yards when maxed out elevation-wise. Come to find out, it was the mounts. Remington 700 mounts are what is usually recommended for them and they fit, but there is a slight difference in the height needed for for the Vanguard vs the 700. You couldn't see it in how the scope was mounted or anything, but it's there. That tiny difference is what was throwing it off that much. I got a mount specifically for the Vanguard, but I haven't had it out yet so I have yet to confirm that fixed the issue, but seems like a solid bet with all the information I have.

 

[jmr40]

I got a mount specifically for the Vanguard

Vanguard and Rem 700 use the same mounts with one exception. If trying to use one piece bases on a short action they are different. And it would be impossible to mount the wrong base. It wouldn't be close. Long actions are 100% interchangeable as are 2 piece bases on either long or short action.

Long and short actions are the same length, but Vanguard has a longer loading/ejection port on their short actions. That means hole spacing for mounts are farther apart. It doesn't matter with 2 piece mounts, but a one piece mount on the wrong short action rifle wouldn't come close to working.

The rear base on either is a tiny bit thicker than the front base. It might have been possible for you to have reversed the mounts. That would have resulted in the scope being angled upward slightly and the rifle would have been hitting very low.

 

[BigBL87]

Vanguard and Rem 700 use the same mounts with one exception. If trying to use one piece bases on a short action they are different. And it would be impossible to mount the wrong base. It wouldn't be close. Long actions are 100% interchangeable as are 2 piece bases on either long or short action.

Long and short actions are the same length, but Vanguard has a longer loading/ejection port on their short actions. That means hole spacing for mounts are farther apart. It doesn't matter with 2 piece mounts, but a one piece mount on the wrong short action rifle wouldn't come close to working.

The rear base on either is a tiny bit thicker than the front base. It might have been possible for you to have reversed the mounts. That would have resulted in the scope being angled upward slightly and the rifle would have been hitting very low.

Could very well be it. I thought I tried reversing them and the screws didn't line up or something like that, but it was last year so I can't say for sure. In any event, I actually prefer the DNZ Game Reaper mount I got for it anyway so alls well that ends well.

 

[BigBL87]

I got curious so I checked the mounts, the screws are farther apart on one and it looks like the curvature is different as well, so I don't think I could have reversed them.

What I ended up coming across on Weatherby boards at the time, guys said there was a small difference in the thickness of the back mount required for a Vanguard vs a 700, and that's what was throwing things off. I suppose when I get around to shooting it again, I'll find out. If it's still low, then it must be the action. That being said, I've read about enough people having the issue to know it's not unheard of.

Could also be that one or both of the Warne bases is out of spec too, who knows. In any event, it's not a super rare issue with Weatherbys/Howas based on my research.

 

[wiscoaster]

sorry, deleted