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Scope consistency issue

Printed From: OpticsTalk by SWFA, Inc.
Category: Scopes
Forum Name: Tactical Scopes
Forum Description: Police and military tools of the trade
Printed Date: June/23/2018 at 22:27
Software Version: Web Wiz Forums 11.10 -

Topic: Scope consistency issue
Posted By: sdjnwest
Subject: Scope consistency issue
Date Posted: October/16/2016 at 22:13
I am having a very difficult to solve issue with my AR and was wondering if anyone else has had this experience with an optic.  The AR is a build up with Anderson lower, Anderson upper, and Faxon barrel and I mounted a Vortex Strike Eagle on it initially with an Aero Precision Ultralight offset mount. 

The kinds of issues I was having right from the start was 3.5-4 MOA groups at 50, 100, and 200 yards with pretty much any ammo I tried.  The scope would also intermittently go out of focus at 6X but the image would look sharp at 4X and below.  I sent the scope to Vortex and they could not find anything wrong with it in their checks and even shot a 3 shot group with it on a bolt gun that was 3/4" I believe at 100 yards.  They suspected the torque used on the Aero Precision mount was high (15 in-lbs) because of loctite applied to the threads during installation causing the scope tube to go oval and advised using 10-12 in-lbs and no loctite.

So got the scope back and tried their advice without any real change.  Switched the mount to a Vortex 2" offset mount and the focus issues seem to have been corrected, but I still get 3.5+ MOA groups.  Suspecting the rifle at this point I sent the scope and rifle to the rifle seller for troubleshooting.

They also could not get under a 4" group at 100 yards with the Strike Eagle mounted and mounted a Trijicon 3-9x Accupower.  Their 3 shot groups with the Trijicon mounted were about 1" at 100 yards.  That seems to exonerate the rifle, but I asked them to shoot a 10 round group just to make sure and I'm waiting on that result.

Has anyone seen a scope act like this before?  Any ideas what the issue could be?  If the 10 shot group says the rifle is good I'm planning to get back with Vortex for next steps.

Thanks for any help.

Posted By: Rancid Coolaid
Date Posted: October/17/2016 at 06:11
First, yes, over-torquing a scope mount can indeed lead to issues with scope consistency. Additionally, if you over-torqued to the point of damaging the scope tube, yes, crazy things can happen to the internal mechanics of the scope.
Did you use a torque wrench?
How much experience do you have mounting scopes?
Is the rifle seller also the rifle builder?

The plural of "anecdote" is not "data."

Posted By: sdjnwest
Date Posted: October/17/2016 at 06:42
Yes actually the place I bought the scope from mounted it and used a torque wrench set at 15 in-lbs. But they put loctite on the screws which Vortex guy said would end up lubricating the threads and causing overtorque. When I got the scope back I mounted it and used a torque wrench set to 10 in-lbs with no loctite per their directions as they said 15 in-lbs was too much for the Aero Precision mount since it clamshells over the tube.

When I swapped mounts to the Vortex mount I mounted the scope again with a torque wrench set to 15 in-lbs but with no loctite.   I don't have much scope mounting experience.

The rifle seller is also the rifle builder.

Posted By: Rancid Coolaid
Date Posted: October/17/2016 at 07:10
Scope mounting is fairly simple, with just a few guiding rules. Rule #1 is use a good torque wrench set to mount manufacturer's specified torque.

If you bought it from Carter's or the like, NEVER let them mount a scope. Ever!

Let us know how it does with the new mount.

The plural of "anecdote" is not "data."

Posted By: sdjnwest
Date Posted: October/17/2016 at 07:43
It was a small tactical rifle shop that did the initial mounting. 

So a little more on the new Vortex mount - I was saying in the first post that using that mount seemed to fix the focus issues.  The focus issue was with focus through the scope looking at the target rather than focus of the reticle.  The reticle focus was never an issue, but when I was using the Aero Precision mount the target focus could change from shot to shot from the shock of the shot.  Weird thing was that was only at 5-6x (I was shooting with it at 6x all the time) and if I adjusted the power down it would clear up from 1-4x but still go out of focus when moving it back up to 5-6x.  After switching to the Vortex mount the focus issue looks to be corrected, but I still have the issue of 3.5+ MOA groups.

I guess the Strike Eagle did not like being clamped from the side with a clamshell ring.  I noticed most other mounts including the Vortex one I got clamps from the top with screws on both sides of the ring.  As I torqued it I also made sure to work my way up to the final torque crossing both sides in an X pattern rather than torquing one side all the way down and then the other.

Posted By: Sparky
Date Posted: October/18/2016 at 21:21
Originally posted by sdjnwest sdjnwest wrote:

but I still have the issue of 3.5+ MOA groups.

What is the twist of the barrel you are using and what gn ammo are you shooting? Also what type of torque wrench are you using?

Posted By: sdjnwest
Date Posted: October/18/2016 at 22:21
Barrel is 16" 1:8 twist Faxon 416R stainless.  Torque wrench is a Husky micrometer adjustable torque screwdriver with +/-6% accuracy from 8 to 40 in-lbs.

I've mainly shot 55 gr ammo in Hornady, PMC, UMC, and Winchester.  Also have shot some Aguila in 62 gr.  Nothing gets better than about 3.5 MOA but several have been much worse.

Posted By: Rancid Coolaid
Date Posted: October/19/2016 at 07:20
Do you have iron backups?  Do you have access to another optic?  Do you have a gun of known precision and accuracy on which you could mount this optic?

Where do you shoot in/around Houston?

Greater than 3 MOA at 100 yards is indeed terrible, there is an issue, with that I heartily agree.

The plural of "anecdote" is not "data."

Posted By: sdjnwest
Date Posted: October/19/2016 at 07:52
I have iron backups but my near vision keeps them blurry for me, hence the desire for a 1-6x optic on the rifle.  Using another optic is what the rifle seller also suggested, but since I didn't have one (or another rifle) I gave the rifle and scope to them to try with another optic and they used a Trijicon 3-9x Accupower and got 1 MOA groups at 100 yards, but they were 3 shot groups.  I've asked them to do a 10 shot group for me just to completely exonerate the rifle in my mind (I've had some decent 3 shot groups with the Strike Eagle, but never with a 10 shot group).  They still have the rifle right now but I should get it back in a week or so.

As for shooting location I recently joined PSC Shooting Club down in Friendswood.

Posted By: Rancid Coolaid
Date Posted: October/19/2016 at 08:12
Okay, sounds like you are on the right track.  There isn't much we can do to trouble-shoot this remotely other than make the suggestions already made.

To clarify: Vortex says the optic is fine, the builder says their Trijicon Accupoint shot 1 MOA or better, and you swapped mounts on the Vortex - from the Aero to the Vortex - with no improvement in performance?

You mentioned in the first post that the scope tube went "oval", is the scope still out of round?

The plural of "anecdote" is not "data."

Posted By: sdjnwest
Date Posted: October/19/2016 at 11:12

All correct on the "To clarify" line. 

On the oval scope tube - the Vortex folks suspected that the Aero Precision mount might have caused the tube to go oval some when overtorqued and they mentioned some internal components that would lose contact with each other if this is was the case (not being familiar with the internals I didn't exactly follow - just knew it didn't sound good).  I think they said oval because of the way the Aero mount clamshells over the tube with screws only on one side of the ring.  Their inspection said everything was ok though so it didn't sound like the oval was permanent.

They offered and I said please do to taking the scope to their range and testing it out.  They mounted it on a Savage bolt gun (don't know the model or caliber or mount they used) and sent me the target they shot which showed a 3/4" group of 3 shots.  I'm pretty sure they said the shots were at 100 yards, but I can't find that written down anywhere.  At this point I thought the Strike Eagle must be ok and the oval was not permanent.

I'm wondering if mounting the scope when I got it back with the Aero mount, even though I followed directions and only torqued to 10 in-lbs, finished some internal damage that can't be recovered now.  Never knew these things could be so tender.

Posted By: Sparky
Date Posted: October/19/2016 at 11:47
Yes it sounds like you are on the right track.

But some other thoughts come to mind. Such as what is the torque setting for the ring base?
How are you shooting your groups? Off a bag, bipod or something else?
How fast are you shooting your groups?
Is there someone else who could shoot some groups while you are at the range? Sometimes someone else can see something we don't.

Also please don't be offended, but I am not familiar with the Husky torque wrench and how you know you have reached the correct tightness once you have set the torque wrench. Such as most of mine click when you reach the correct tightness which allows one to over tighten if they keep on turning. And I have seen more than a few mechanics do this. But one of mine just releases once you have reached the correct tightness. 10in-lbs is not very much.

Posted By: sdjnwest
Date Posted: October/19/2016 at 13:01
I've been taking the base to 25 in-lbs. 

Groups are shot from a rest with a bag under the fore end and a bag under the handgrip.  I squeeze the bag under the handgrip to change elevation and get on target.  I also got some 10 round clips so I can rest easier on the bench - 30 round clip sticks down too much for a good stable bench rest.

I've been trying to keep the pace slow when shooting by looking through my spotter between each shot.  I haven't yet, but plan to start noting the placement of each shot on a piece of paper at the bench to look for trends from shot to shot.

I haven't yet asked anyone else to shoot it other than the rifle builder who has it now.  They reported similar 4" groups at 100 yards when using the Strike Eagle, but 1" groups when using their Trijicon.

The Husky I picked up at Home Depot.  It does release when you reach torque and rotates freely about a 1/4 turn before it engages again.  If you keep turning it just keeps releasing so I don't think it is overtightening.  Agree 10 in-lbs isn't much and I wasn't so sure how well it would hold the tube, but that's what I did.  When I switched to the Vortex mount I went back up to 15 in-lbs on the rings.

Thanks for you guys (Rancid and Sparky) taking the time to offer suggestions.  From the lack of response from other folks I take it no-one else has experienced this kind of insidious issue. Loco

Posted By: Sparky
Date Posted: October/19/2016 at 13:33
Originally posted by sdjnwest sdjnwest wrote:

I've been taking the base to 25 in-lbs. 

Groups are shot from a rest with a bag under the fore end and a bag under the handgrip.  I squeeze the bag under the handgrip to change elevation and get on target. 

Thanks for you guys (Rancid and Sparky) taking the time to offer suggestions.  From the lack of response from other folks I take it no-one else has experienced this kind of insidious issue. Loco

You are very welcome! So many people have taken the time to help me when I was new. It is a privilege to return the favor and help others.

I would try moving the rear bag from under the handgrip to the buttstock and slide the rifle forward or aft to change the elevation keeping the stock on the bag. This is assuming you have an A2 buttstock, but still put the bag under the buttstock regardless of what type of buttstock you use. The rifle is suppose to slide on the bag(s) during the recoil and I think the bag maybe getting hung up on the handgrip. Some benchrest shooters I know even use a powder like talc powder to help smooth out the sliding of the rifle. Also when you say the front bag is under the fore end I am assuming it is not touching the barrel. Not sure why the builder was getting 4 inch groups, but I would definitely try moving the bag from the handgrip to the buttstock.

Everything else you are doing looks good to me.

Posted By: sdjnwest
Date Posted: October/19/2016 at 14:28
I'll try that with the rear bag.  It's not an A2 buttstock, it's a Hogue adjustable buttstock but the adjustment lever is covered by an angled piece so it won't hit the bag and trip.

And yes, the barrel is free-floating inside the fore end handguard and the bag is under the handguard.

Posted By: sdjnwest
Date Posted: November/04/2016 at 14:43
Sorry it's been a while but I just got my rifle back from the builder this week.  Is there some way to post images in our replies?  If so I can put pictures of the targets.

Their results with the Strike Eagle for a 8 shot group were like mine, about 3-3.5" at 100 yards.  They actually shot a ~20 shot group with their 3-9x Trijicon Accupower and all but one of them were inside a 1" group with one falling outside the main group.  To me that says the rifle is good and there's a problem with the Strike Eagle.

I called Vortex and they sent me a shipping label to send the scope in.  We'll see what they find next week.

Posted By: koshkin
Date Posted: November/04/2016 at 22:37
Based on what I saw in this thread, the problem is likely a combination of the mount and the scope.

Generally, a little while back I got my hands on three Aero Precision mounts and have spent some time messing with them.  All apply uneven pressure onto the scope tube and with some scopes it can cause an issue.

I do not have too much mileage with he Strike Eagle, but I have seen this basic design used by a few other brands and it left me soundly unimpressed.  If you want a low range variable from Vortex, extend your budget a bit and get a 1-4x24 PST.

The reason you were only seeing the problem at 6x is that when you change the magnification of a scope, there are a couple of internal lens groups that move.  It is most likely that when you set the scope to 6x, the one of the lens groups moves right under the portion of the tube that was being deformed by the out of round ring.  That would preclude the lens group from moving the way it is supposed and possibly make it susceptible to recoil.

Have you tried shooting groups at lower magnifications? like 3x or 2x?

It is entirely possible that the scope is damaged and I am sure Vortex will take care of you.  However, with the Aero Precision mounts I have, I concluded that in order to use them, they will have to be lapped and only used on guns with minimal recoil.


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Posted By: sdjnwest
Date Posted: November/05/2016 at 23:29
Thanks koshkin, I've pretty much concluded the problem is this scope doesn't like the Aero mount.  When I sent the scope in to Vortex I also included both the Aero mount and the Vortex mount with it in case it helps them.

I did not try groups at lower magnifications.  I had thought about the 1-4X PST, but really wanted the extra 2X of the Strike Eagle.  Kind of wishing I hadn't done that.

Posted By: koshkin
Date Posted: November/06/2016 at 16:05
Whether that extra magnification is beneficial or not depends on your usage, but as a general rule I tend to choose quality over specs.  That of course depends on the price range: the higher up you go in price the more you get into the diminishing returns territory.  However, that phenomenon is nto really that pronounced until you get above $1k.

In the $500 and under range, there are three low range variables I routinely recommend for ARs and I have yet to get a complaint: SWFA SSDM 1-4x24, HiLux CMR4 1-4x24 and Vortex PST 1-4x24.  The choice between these largely comes down to personal preferences, since they have different turret arrangements, reticles, etc.

The cheapest 1-6x scope I am comfortable with is Styrka S7 1-6x24 that appears pretty well built and has held up pretty well so far.    Still, it costs north of $500.  Aside from that if you want a higher erector ration than 1-4x, you pretty much have to go to Sightron S-Tac 1-7x24 or Leupold VX-6 1-6x24.

Right now, SWFA has good discounts on Tango6 1-6x24 as well.

In the sub-$500 range getting too ambitious with specs is usually not worth it, in my opinion.


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Posted By: sdjnwest
Date Posted: November/25/2016 at 21:51
I finally have success with my rifle and the Strike Eagle.  The Vortex folks received the scope and disassembled it, reassembled it, and shot a number of 3/4" 3 shot groups to put the scope through its paces.  Even though they reportedly didn't find anything wrong with it, the rattle that was there when I sent it to them was gone when I got it back.

I mounted the scope with a 2" offset Vortex mount and went to the range today.  With Hornady V-max ammo I was able to get 1.2 MOA 10 shot groups at 100 and 200 yards.  Remington UMC ammo gave me about 2 MOA.   The problem looks to be solved.

Not sure why, but the Strike Eagle does not perform well with the Aero Precision Ultralight.

Posted By: urbaneruralite
Date Posted: November/26/2016 at 12:53
Was the scope rattling the whole time?

Posted By: sdjnwest
Date Posted: November/26/2016 at 20:54
Not when I first got it, but it started after using the Aero Precision mount. 

Posted By: HKtoTikka
Date Posted: September/28/2017 at 12:34
Message to self: Never use Aero Precision mounts.

Posted By: Kickboxer
Date Posted: September/28/2017 at 17:48
I have used Aero Precision mounts… just trying them out.

Then I used them as targets for my 50BMG…   I'll see if I can locate them and take pictures.  They are great targets… require you to really concentrate.  Lousy mounts… in my opinion.

Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living

Posted By: koshkin
Date Posted: September/28/2017 at 18:55
I have several of Aero Precision mounts and I am deeply unimpressed, although I figured out how to make them work (not on all scopes).

On a different note, since this thread started I stumbled onto another reasonably inexpensive 1-6x24 scope that I like more than most other options in the same price range: Burris RT6.  I did not expect much of it, originally, but once I got it onto the rifle it turned out to be a very pleasant surprise.


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