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Scope mount rubbing


Cinders
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While trying to track down a strange inaccuracy issue where I'd get a tight 3 round group in one spot and then a tight 2 round group 2 inches over to the right (rinse and repeat every grouping), I came across rub marks where the scope mount is rubbing, possibly the cause of the issue.  

The scope mount in the picture isn't where it was before, I had the scope mount 1 notch forward so it bridge onto the first notch of the shroud.  After noticing the rubbing, I moved the mount back a notch to see if that fixed the problem (haven't been able to go shooting yet), but I can see the 2 points of contact again (2nd picture).

Can I get some advice on this?  Do I have the scope mount backwards?  Should I file it down to fix the rub points?  Am I doing something wrong here?

 

Thanks!

 

 

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6 hours ago, unforgiven said:

You pushed it forward and tighten to spec? Rubbing is usually caused by movement. Just my 2 mags

Not sure what you mean on pushed forward.  The front scope mount was on the first notch of the shroud rail and the 2nd mounting point was on the main body of the AR rail.  I'm seeing that metal rubbing (sorry for blurry pic) on the shroud rail where the scope mount was touching it.  I do suspect movement as well, but the question is why and what to do about it.

Questions:

1) Should the shroud rail be moving like that to cause that rubbing?

2) Should the scope mount be touching the rail like that?

3) Moving the scope mount to be completely on the AR upper rail is a good solution?  Or should I look at returning the mount or modifying it?

 

Thanks for any advice?

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On 12/21/2021 at 8:54 PM, 98Z5V said:

@Cinders, can you get this done?  Post the pic of the overall gun. 

I agree, we can't tell if you scope mount is backwards without being able to see the whole mount. Nice, sharp, up close pictures (which yours certainly are) are great at times but other times an overall pic can be more useful.

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Sorry for the delay, been stuck on non-stop 24 hour shifts due to holidays and staffing (thanks corrupt politicians for ignoring major city problems!)

Thanks for the replies thus far.  I should be headed to the range this coming week to test if the rubbing was the issue.

Attached is a distant photo.  Note: I moved the scope mount back 1 lug, this is after I saw the rubbing.  Originally, the front of the scope mount was on the first shroud lug (bridging the shroud and the upper).

I emailed American Defense and got a lackluster reply that repeated what I had said the problem was.  I asked them if I have the mount backwards or why does the scope mount have 2 weird points of contact.  Response:

"Thank you for contacting us.

 

It looks like the rail may be shifting under recoil or the rail lugs are taller than normal and are rubbing on high spots on the rail."

 

20211227_153507.thumb.jpg.0aa590bb5451b3dc03af840c9c91ee48.jpg

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@CindersShould be good to go. The levers are on the left side so the mount is oriented correct, but honestly it probably wouldn't make a difference since it's not a cantilevered mount. Just make sure it's torqued down on the rail. My ADM mounts are all set up so they take a fair bit of force to lock down and are somewhat of a pain to remove. I'd say go shoot it and see if it's fixed. I'd also say I have a tendency to make a similar 3/2 shot group and I'm pretty sure it's me but Ive seen people suggest the barrel is warming up on the last two. 

 

Also, instead of quoting, you can plug in someone's user name after the @ symbol to tag them. 

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7 hours ago, Cinders said:

 

 

20211227_153507.thumb.jpg.0aa590bb5451b3dc03af840c9c91ee48.jpg

Scope position on the rifle is good - the scope eyepiece should be at the end of the upper receiver - and yours is.  If it's not, if fuks up eye relief for "normal people." Scope position ON THE GUN is good.

Here's an EASY solution.  MOVE THE SCOPE MOUNT BACK, so it's not bridging the gap to the upper receiver rail.  That will entail that you MOVE TO SCOPE FORWARD in the mount - and you have plenty of room to do that, from the pic. 

That will fix everything that's scope-mount related, in this whole issue.  It's simple.  :thumbup:

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I have a mount of that style with a PA 4x16 I use for test firing and breaking in new rifles. Almost always have to adjust the levers to get the tension right for each rail, if it's easy to open the levers then it ain't tight enough, ADM's directions on that seemed a bit misleading to me. I usually end up with some wear marks right ahead of that front lever as well, can't say it's been an issue. 

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On 12/28/2021 at 8:19 AM, jtallen83 said:

I have a mount of that style with a PA 4x16 I use for test firing and breaking in new rifles. Almost always have to adjust the levers to get the tension right for each rail, if it's easy to open the levers then it ain't tight enough, ADM's directions on that seemed a bit misleading to me. I usually end up with some wear marks right ahead of that front lever as well, can't say it's been an issue. 

I'm contemplating doing a single pass with a file across those 2 friction points on the scope mount.  I can't see anything positive coming out of the 2 contact points.  Plus it rubs down the metal

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7 hours ago, Cinders said:

I'm contemplating doing a single pass with a file across those 2 friction points on the scope mount.  I can't see anything positive coming out of the 2 contact points.  Plus it rubs down the metal

That'll work.  :thumbup:

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  • 2 weeks later...

Solved! 

Thanks for the help and advice, everyone!  I was getting a weird pattern before: firing at one point, I would get 2 distinct, tight groups split by several inches.  After taking it apart, we figured that the barrel and comp were torqued correctly, the gas tube was correct and not rubbing, and the shroud was not rubbing either.  The scope mount was very tight and torqued to specs.

It appears to have been this rubbing issue with the scope touching the shroud railing.  I moved it back a lug to be fully on the upper receiver and the problem seems to have gone away.

Note: not a split group in picture, that was me dialing the scope in on 2 different groupings.

20220106_140504.jpg

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