View Full Version : Eotech sliding when hand tight
I have a BCM complete rifle (2013) that has never had anything on it other than backup sights. Recently purchased a Eotech EXPS2-0 and after doing some cleaning noticed the sight had shifted toward the stock end of the gun. I had mounted it tight (to where it would not slide by hand and felt sung) against the muzzle end of the rail section and added one more click to the adjustment screw. Still if send the bolt home a half a dozen times I can see a shift away toward the stock. Any tighter I am afraid I will damage the QD lever...is this normal with sending the bolt into battery but stays in place at the front end of the rail section during recoil? I would think that it would stay put but this is my first rifle and optic. Thanks
I wouldn't worry about it. I've had two uppers that required the EXPS to have a few adjustments before it stayed tight. Others it was tight & never moved right from the get go.
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I wouldn't worry about it. I've had two uppers that required the EXPS to have a few adjustments before it stayed tight. Others it was tight & never moved right from the get go.
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Is this due to finish wear? I do notice that it is showing rub marks on the sight and the rail hasn't lost finish, but you can see where pressure has been applied. Finish wear doesn't bug me, a sight that moves when releasing the bolt catch does. Again another click on the adjustment screw feels like I have to put decent leverage into it.
Is this due to finish wear? I do notice that it is showing rub marks on the sight and the rail hasn't lost finish, but you can see where pressure has been applied. Finish wear doesn't bug me, a sight that moves when releasing the bolt catch does. Again another click on the adjustment screw feels like I have to put decent leverage into it.
I've always attributed it to a slight crush of the rail although I never measured anything to confirm. Coincidentally, the two uppers I had to readjust the EXPS to were also BCM's. I had it on a Colt for over a year first and never had to readjust it after the first initial mount. It wasn't until I played musical RDS that I noticed it required readjusting on those two particular uppers. All my other uppers are fine. I've since settled into a configuration that I like & it hasn't moved since. Don't worry about the added pressure required after the adjustment. It shouldn't require anything more than just your hand to snap it in place but it may take a firm push to lock it in.
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Shim with a little foil, mount the XPS all the way up in the rail slots, apply vibratite to thumbscrew , allow vibratite to dry, torque that sucker in there. My XPS hasn't moved a nm since I installed it.
Shim with a little foil, mount the XPS all the way up in the rail slots, apply vibratite to thumbscrew , allow vibratite to dry, torque that sucker in there. My XPS hasn't moved a nm since I installed it.
The OP has an EXPS, not an XPS. Different mount. The EXPS has a QD lever lock & no thumbscrew.
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Oh my bad, I missed that. Still, shim, vibratite, and there must be a tensioning screw on the QR. Vibratite that.
Once locked in place, there's nothing to rotate. The adjuster has detents. I'd advise against using any thread locker on the the EXPS system.
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I saw this with one of my .30 caliber AR's when I installed a 1x4 scope on a QD mount. Every time I removed the mount, I noticed the same thing you are seeing. I did not notice a zero shift out to 300 yards. I placed tin foil between the mount and upper receiver, shot groups and did not notice any difference in zero, so I removed it.
Adjust the tension on the throw levers until the mount does not appear to move when cycling the charging handle. Lay the mount on top the carbine, slide it to the rear, then throw the levers to tighten it. Unless you are shooting at 500 yards or farther, it should not make enough difference to have a noticeable affect accuracy.
I don't use thread locker on the QD mounts.
Once locked in place, there's nothing to rotate. The adjuster has detents. I'd advise against using any thread locker on the the EXPS system.
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Ahhh.. I only have the XPS.. I always lightly vibratite optics, grip screws, and ambi safety lever screws. Super easy to remove but holds things in place. Sorry for the bad advice.
I've always attributed it to a slight crush of the rail although I never measured anything to confirm. Coincidentally, the two uppers I had to readjust the EXPS to were also BCM's. I had it on a Colt for over a year first and never had to readjust it after the first initial mount. It wasn't until I played musical RDS that I noticed it required readjusting on those two particular uppers. All my other uppers are fine. I've since settled into a configuration that I like & it hasn't moved since. Don't worry about the added pressure required after the adjustment. It shouldn't require anything more than just your hand to snap it in place but it may take a firm push to lock it in.
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If I understand you I will have to let the rail crush until it "sets" with this particular sight and keep adjusting the screw to make it do so? So far it is adjustable with one hand but the next click from the detent will require a good amount of force. I know the adjustment screw is there for different tolerances among rails, but this is normal you are saying to have to keep adjusting?
So if I understand correctly the rail needs t
When mounting anything in the military on a rail, especially an optic, we always get it on the rail and in the slot. Then lightly push it rearward until it contacts the back of the slot. Then tighten it down. The shift is common under recoil and even closing the bolt, but if it is pushed to the back of the slot, it will not have anywhere to shift to. This maintains an accurate zero. I would tighten it a little by following the process above and you will be good to go.
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When mounting anything in the military on a rail, especially an optic, we always get it on the rail and in the slot. Then lightly push it rearward until it contacts the back of the slot. Then tighten it down. The shift is common under recoil and even closing the bolt, but if it is pushed to the back of the slot, it will not have anywhere to shift to. This maintains an accurate zero. I would tighten it a little by following the process above and you will be good to go.
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By push to the rear do you mean the portion of the rail closest to the front sight or to the buffer tube? I have mine pushed to the front sight side of the slot when tightened. It appears to shift toward the buffer tube when cycling the bolt, but maybe when shooting a mag the amount of recoil force cancels out the bolt cycling.
If I understand you I will have to let the rail crush until it "sets" with this particular sight and keep adjusting the screw to make it do so? So far it is adjustable with one hand but the next click from the detent will require a good amount of force. I know the adjustment screw is there for different tolerances among rails, but this is normal you are saying to have to keep adjusting?
So if I understand correctly the rail needs t
I've only had to readjust a couple of times before it remained in place. It shouldn't require tools but quite possibly two hands.
FWIW, based on my experiences & what I've read here, optics should be pushed forward in the rail prior to tightening it down.
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I've only had to readjust a couple of times before it remained in place. It shouldn't require tools but quite possibly two hands.
FWIW, based on my experiences & what I've read here, optics should be pushed forward in the rail prior to tightening it down.
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This would be my first time adjusting it one click tighter after initial fitting when I got the sight. I also heard here and elsewhere that it needs to be pushed forward
Slow work day so I called Eotech. Paraphrasing ...... but the rep stated it should not be moving and as long as I do not need tools to put it on and remove it I am ok, but also mentioned on some rails if the finish is thicker the sight may need to compress that down for it to settle. Maybe BCM has thicker coatings on their uppers?
I have also come across the comment that the mount should be pushed forward before tigntning down. We could be talking a very slight movement here but--Any opines one way or the other as to why?
I have also come across the comment that the mount should be pushed forward before tigntning down. We could be talking a very slight movement here but--Any opines one way or the other as to why?
In the simplest way I can explain it.....
Recoil has a rearward and a forward impulse. You should push the mount toward the muzzle when installing to support it during the forward impulse. When mounting toward the charging handle, the mount MAY work itself forward during the forward impulse.
I have also come across the comment that the mount should be pushed forward before tigntning down. We could be talking a very slight movement here but--Any opines one way or the other as to why?
https://www.m4carbine.net/showthread.php?113159-Mounting-things-more-to-the-rear-or-front-of-the-rail-slot
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I have also come across the comment that the mount should be pushed forward before tigntning down. We could be talking a very slight movement here but--Any opines one way or the other as to why?
The mount seems to work it's way back as you fire the weapon, so I like to push the mount to the rear before tightening. That way when I zero an optic, nothing should change when I remove and reinstall the mount.
By push to the rear do you mean the portion of the rail closest to the front sight or to the buffer tube? I have mine pushed to the front sight side of the slot when tightened. It appears to shift toward the buffer tube when cycling the bolt, but maybe when shooting a mag the amount of recoil force cancels out the bolt cycling.
Towards the Buffer Tube is what I meant by towards the rear. What happens is when the rifle is fired, the whole rifle including the optics is pushed back in the direction of the butt stock or shooter, opposite of teh bullet (equal and opposite of the bullet). When the rifle comes in contact with the shoulder of the shooter, it slows and stops the rifle, but the attachments are still moving from that momentum if they are loose or do not have enough friction to hold in place, until they can meet something to stop them. If you push the optic rearward towards the buffer tube/butt stock within the 1913 rail slot, it will already be in contact with the rifle and its momentum will stop with the rifle.
Failure2Stop
07-14-14, 23:07
Ahem.
Optics should be mounted with contact forward.
The optic has greater inertia on the initial recoil than at any other point in the cycle.
For greatest consistency, mount forward.
References:
Leupold
Trijicon
KAC
KnightVision (division of KAC)
US Army
USMC
You are correct, it should be pushed forward towards the muzzle. Sorry for spreading mis-information.
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Ahem.
Optics should be mounted with contact forward.
The optic has greater inertia on the initial recoil than at any other point in the cycle.
For greatest consistency, mount forward.
References:
Leupold
Trijicon
KAC
KnightVision (division of KAC)
US Army
USMC
I have seen my QD mounts move to the rear after the weapon is fired several times. What is your opinion on how it effects accuracy if the mount is pushed forward before zeroing the optic?
I was able to add a couple more notches of adjustment where the eotech does not seem to move after releasing the bolt a few times, but it is one hand tight that may require two or even more leverage if I were to do one more notch. Plan on shooting it tomorrow or thursday to see if it stays put. I can tell there is more finish being compressed so being a new sight and fresh upper something seems to be breaking in possibly
I have seen my QD mounts move to the rear after the weapon is fired several times. What is your opinion on how it effects accuracy if the mount is pushed forward before zeroing the optic?
Mine started to slide again....but this time it was less and was able to do 2 more clicks again on the adjustment nob where before it was as tight as I could get it. Anyone have any ideas on whether something is stretching out? There is not any deformation of the rail just some compression of the finish on the rail....bit confused here. Thanks
Mine started to slide again....but this time it was less and was able to do 2 more clicks again on the adjustment nob where before it was as tight as I could get it. Anyone have any ideas on whether something is stretching out? There is not any deformation of the rail just some compression of the finish on the rail....bit confused here. Thanks
I would like to hear the answer to this too. I have been contemplating getting an Eotech my self that will end up going on a new upper.
Ahem.
Optics should be mounted with contact forward.
The optic has greater inertia on the initial recoil than at any other point in the cycle.
For greatest consistency, mount forward.
References:
Leupold
Trijicon
KAC
KnightVision (division of KAC)
US Army
USMC
This.... I have an XPS on a Fortis REV mounted far forward and it hasn't moved a micrometer in over 1500 rounds.
Failure2Stop
07-27-14, 13:58
I have seen my QD mounts move to the rear after the weapon is fired several times. What is your opinion on how it effects accuracy if the mount is pushed forward before zeroing the optic?
Insufficient tightness on the mount.
Definately not good if it's shifting.
Insufficient tightness on the mount.
Definately not good if it's shifting.
Mine is TIGHT...BCM upper with 14.5 barrel and BCM comp. I would think things on my end are good to go normally. Do comps that reduce recoil make the bolt have more rearward shift on an optic making them move to the rear? Very close buddy of mine (USMC combat weapons instructor) stated that he has seen optics move to the rear from recoil, but the rifle will still be able to shoot better groups than the shooter...
Good info . I have a new colt and have on order a exps2-0
I will keep a eye on this .
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