trouble with an EoTech 512

trouble with an EoTech 512

This is a discussion on trouble with an EoTech 512 within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; Recently put an Eotech 512 on AR. Zeroed it at about 30 yds.Decided to add a BUIS,which forced me to move the 512 forward on ...

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Thread: trouble with an EoTech 512

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    Member Array Hawkerdriver's Avatar
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    trouble with an EoTech 512

    Recently put an Eotech 512 on AR. Zeroed it at about 30 yds.Decided to add a BUIS,which forced me to move the 512 forward on the rail. Now the Eotech is all over the place no matter which way I adjust it.I have checked the mounting on the rail..it's square and seated properly.

    Two questions: 1.) By moving a pre-zeroed red dot optic on the rail,typically how much does that change earlier zero?(I have made BIG adjustments on elevetion / windage to try and correct it but to no avail.Everything goes to left shoulder area when using a B27 type target.Aim point is center of head.
    2.) Once BUIS is zeroed,am I correct in thinking there are really two zeroing goals here? One for each,regardless of how they co-witness?


  2. #2
    Distinguished Member Array airslot's Avatar
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    Ck the amount of deflection in the rail itself. Mine is mounted on a DD Omega rail with no problem being mounted to allow NV behind it.
    The situation will NEVER BE THE WAY YOU WANT, it WILL BE THE WAY IT IS. You must be FLEXIBLE ENOUGH TO ADAPT and just "DEAL WITH IT".

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    What kind of rail are you running? Many lower end rails are not solid enough to mount an optic on. Whenever possibly, an optic should be mounted on top of the reciever.

    There will be significant changes in the POI as you move the optic, as you have seen. How far you moved it will determine how much the POI is changed.

    As for question 2, when both are zero'd they should be pretty close together.
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  4. #4
    Member Array Hawkerdriver's Avatar
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    Zeroed optic @ 50 yds.Took about 50 rounds it was so bad off. When I finnished and started putting gear away,noticed that the E512 had worked it's self slightly loose on the rail.Tightened it back up without changing rail posit,but as sensitive as these things seem to be,i reckon it's back to the range to re-zero. The rail is part of an after market upper I installed on an older Bushmaster that had the permanent carry handle.I"m getting the hang of zeroing the optic,but then there's this-I installed a MBUIS Gen2 on the upper rail for co-witness.With optics OFF,and using the 6 O'clock reference for front sight line up,I had to crank it almost all the way to the right to get close to the 9 ring..I did all the shooting prone with sandbags for support.Didn't have access to a shooter's table..The iron sight issue has me a little worried.. Thanks!

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    VIP Member Array aus71383's Avatar
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    If it works itself loose shooting 50 rounds, it's a waste of ammo to even zero it. You could just "hope" your rounds at the target.

    But seriously - there is some more information needed here. Did you buy the EOTech new? Do you have the manual?
    What ammo are you using? Why are you zeroing your optic at 30 yards and then at 50 yards? What is your intended zero distance?
    Who made your upper? What are the barrel markings? Does it have a fixed front sight? Are there any front sight markings? Did you just buy a flat top upper and swap it with the carry handle one, or did you buy a complete upper receiver?
    Where on your upper receiver did you mount the MBUS? Where on your upper receiver did you mount your EOTech?

    http://lib.store.yahoo.net/lib/optic...ght-manual.pdf

    Here's the mounting excerpt:

    1. Locate the post and dovetail clamp on the underside of the sight. Loosen the hex nut retainer screw and the dovetail clamp with the allen wrench (7/64")
    2. Place the post within a groove on the top of the 1" dovetail base. Individual preference and the specific firearm determine the optimal positioning to any specific groove on the dovetail base.
    3. Make sure the post is inserted fully into the mount’s groove and push the sight as far forward as possible. Tighten hex nut and retainer screw.

    And most importantly - if you're mounting something on a rifle, use blue locktite and witness marks. Then you can quickly glance at your witness makes to ensure that they are still lined up and nothing has wiggled loose.

    For the irons - I'm trying to picture what you're describing with the optic off and using 6 to get to the 9 ring. Are you saying that you used a 6 o'clock hold with your aiming? Typically sights are designed for a dead center hold. 6 o'clock could mean a lot of things, depending on the size of the target and the distance to it. As for the 9 ring - does this mean you were hitting low, high, left, or right? Since you said you had to crank it all the way to the right - you were cranking the windage adjustment, that makes sense. Were any elevation adjustments necessary? Which aperture were you using on the rear sight?

    Don't worry too much about the iron sights - we'll get it figured out.

    Austin

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    VIP Member Array varob's Avatar
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    Once you've got the :EOtech where you want it, use Blue Lock Tite on the screws, then scratch a visual reference mark on the screw head and the rail so you can check to see if it's secure at a glance.
    Don't believe what you hear and only half of what you see!
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    Member Array Hawkerdriver's Avatar
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    aus71383- I will try to answer your questions best I can in order..
    1.Bought E512 NEW,have manual.
    2.Started @ 30yds,found a better range to zero at 50.My reasearch led me to believe this is the best all around distance for that.
    3.Just bought a flat top upper to replace old carry handle style.Had gunsmith install original barrell/barrell nut/gas cylinder so i would know it was done right.Dont know brand of upper reciever.
    4.Fixed front sight,also original Bushmaster equipment.No markings.
    5.MBUIS is mounted as far aft as possible,E512 is mounted just forward of the T8 slot on rail.
    Hope this helps,and thanks for yours! HD

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    Array Tangle's Avatar
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    Hmmm, based on the title, I was gonna say cost and short battery life but, I see it's a different problem
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  9. #9
    VIP Member Array aus71383's Avatar
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    It could be that the gunsmith who installed your new barrel on your old upper didn't align the barrel perpendicular to the receiver - this would explain the extreme windage adjustments required to get near the center of the target. I can't see your gun - but maybe put a level on the upper receiver and see if there is any obvious "tilt" to the front sight. If so, the barrel isn't on straight. This would not cause the EOTech to shoot "all over the place" though. It would just require extreme windage adjustments to zero the irons.

    He/she could also have installed the barrel nut too loosely or improperly - which would cause the gun to shoot all over the place. If you can push on the front sight from left to right and it moves a little - that is the entire barrel turning. I doubt this is happening, but it's theoretically possible. It would explain the EOTech shooting "all over the place" - but it wouldn't explain the irons needing extreme windage to one side.

    It's clear that you didn't have the EOTech mounted properly - it shot loose in a single trip to the range. Having an optic (or irons) mounted on a rail without them being secure will definitely cause problems. You could get lucky and hit a few times in the same place, but there's no way for it to be consistent unless the sights are mounted securely on the receiver.

    Let's assume that your gunsmith did everything just right.

    I don't have MBUS sights myself - but I would guess they use a flat head screwdriver to mount to the receiver. I would also guess they come with an instruction booklet that says you should have the sight all the way forward in the slot on the rail when tightening the sight, and it might even say how tight you should have it. Personally, I do my mounting "GRRRR" tight with a screwdriver (using lock tite).
    There are 2 different apertures on the sight. A giant hole and a tiny hole.
    Which were you using?
    Are you familiar with peep sights?
    Were you using a sling? If so how does it attach?
    Do you know how many clicks of windage are in your rear sight?
    What length is your barrel?
    Did you make any elevation adjustments when sighting in the irons?

    Irons are important. If you get your irons on right, and zeroed properly, all you'll have to do with the EOTech is (mount it securely) turn it on and adjust until it aligns with the iron sight picture.

    As for the EOTech - I would suspect nothing is wrong with it, and you didn't have it on tight enough. Be sure to push it forward in the slot when tightening.

    Austin

  10. #10
    VIP Member Array jonconsiglio's Avatar
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    Quick question. The EoTech isn't mounted to the hand guard in any way and is only mounted to the upper receiver itself, correct? Or, is the front part of the mount bridging the gap and attaching to a railed hand guard in any way?

    The EoTech 512 is one of the most problematic EoTechs. I'm NOT saying its the issue and I'm NOT saying all 512's are bad. But, it's not out of line to question the 512 in this instance. I would likely not be as quick if it was an Aimpoint or EoTech EXPS.

    If the optic was zeroed before moving it, I would check the mounting first.

    Here's what I would do IF it was zeroed properly and is now completely off after doing nothing more than moving it forward and adding a rear BUIS.

    Very quickly, I'd remove the rear BUIS and move the EoTech back to where it was originally. It should still group tight, though it may be slightly off at 100 yards. EoTech mounts won't necessarily retain a perfect zero like some other mounts, but it'll still group tight and should be close. I'd do this just to check, then move on to the rest.

    I'd remove the EoTech. I'd assure my irons are zeroed properly. I'd then return the EoTech to a mechanical zero while not attached to the rail. After that, I'd check the mount by tightening it and feeling for any movement.

    Now, I'd attach it to the upper receiver. Remember, tighten this thing down while pushing forward. Use some blue Loctite and follow the instructions on how to mount it properly. I'd look through my irons and move the center dot of the reticle to fall perfectly in line with the front and rear irons, essentially lining up all three. (please refer to my sticky on Proper Use and Co-Witnessing of red dot optics in this subforum. Though I use Aimpoints, use is exactly the same. There are pics to illustrate co-witnessing).

    I'd then fire ten rounds using the iron sights with the reticle lining up with them. If the reticle does not line up when viewing though the rear aperture and using the front sight post, it will not be zeroed. If that works, I'd then fold down the BUIS, or just the rear. If they don't fold down, I'd use the optic as intended, viewing the reticle over the irons.

    Viewing the reticle through the irons is NOT how you should use a red dot optic. I cover this in the sticky, but I'm astounded how many do it this way, essentially just painting the front sight post, so I feel it's worth mentioning. Only for zeroing and confirming zero should all three be in line. Not saying you do this, but many, many shooters do.

    This would tell me everything I need to know. If you can do this, we can go from there. But, if it doesn't hold zero at that point, it likely needs a trip back to EoTech.

    Now, I'd zero at 50 or 100 yards. If all I had available was 25 yards, I'd use a 25 yard zeroing target to put me at 100 yards. Also, keep in mind that the impact of your bullet, when zeroed at 30 yards, will be considerable higher than your aiming point at 100 yards, roughly 2" to 3", give or take due to your offset and mount height.

    There's nothing wrong with needing a considerable amount of windage adjustment to zero an optic. Anything within 10 MOA, give or take, is acceptable generally speaking. This will vary with barrel length, optic and my memory!

    This will get worked out, just please read that sticky and try doing what I posted. I know some of this may sound very beginner and for all I know you're a well trained SWAT officer, but I post this way for simplicity and for others that may read it as well. Not trying to insult your knowledge in any way.

    Jon
    Proven combat techniques may not be flashy and may require a bit more physical effort on the part of the shooter. Further, they may not win competition matches, but they will help ensure your survival in a shooting or gunfight on the street. ~Paul Howe

  11. #11
    VIP Member Array jonconsiglio's Avatar
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    Quote Originally Posted by aus71383 View Post
    It could be that the gunsmith who installed your new barrel on your old upper didn't align the barrel perpendicular to the receiver - this would explain the extreme windage adjustments required to get near the center of the target. I can't see your gun - but maybe put a level on the upper receiver and see if there is any obvious "tilt" to the front sight. If so, the barrel isn't on straight. This would not cause the EOTech to shoot "all over the place" though. It would just require extreme windage adjustments to zero the irons.

    He/she could also have installed the barrel nut too loosely or improperly - which would cause the gun to shoot all over the place. If you can push on the front sight from left to right and it moves a little - that is the entire barrel turning. I doubt this is happening, but it's theoretically possible. It would explain the EOTech shooting "all over the place" - but it wouldn't explain the irons needing extreme windage to one side.

    It's clear that you didn't have the EOTech mounted properly - it shot loose in a single trip to the range. Having an optic (or irons) mounted on a rail without them being secure will definitely cause problems. You could get lucky and hit a few times in the same place, but there's no way for it to be consistent unless the sights are mounted securely on the receiver.

    Let's assume that your gunsmith did everything just right.

    I don't have MBUS sights myself - but I would guess they use a flat head screwdriver to mount to the receiver. I would also guess they come with an instruction booklet that says you should have the sight all the way forward in the slot on the rail when tightening the sight, and it might even say how tight you should have it. Personally, I do my mounting "GRRRR" tight with a screwdriver (using lock tite).
    There are 2 different apertures on the sight. A giant hole and a tiny hole.
    Which were you using?
    Are you familiar with peep sights?
    Were you using a sling? If so how does it attach?
    Do you know how many clicks of windage are in your rear sight?
    What length is your barrel?
    Did you make any elevation adjustments when sighting in the irons?

    Irons are important. If you get your irons on right, and zeroed properly, all you'll have to do with the EOTech is (mount it securely) turn it on and adjust until it aligns with the iron sight picture.

    As for the EOTech - I would suspect nothing is wrong with it, and you didn't have it on tight enough. Be sure to push it forward in the slot when tightening.

    Austin
    I missed this post before I typed out my novel. Absolutely check the mount first. Do exactly as Austin stated and push the optic forward then tighten down.

    For whatever reason, I missed that it shot loose. If it shot loose, then there's no question that this is the issue. A dab of blue Loctite or Vibra-Tite will keep the screws from loosening.
    Proven combat techniques may not be flashy and may require a bit more physical effort on the part of the shooter. Further, they may not win competition matches, but they will help ensure your survival in a shooting or gunfight on the street. ~Paul Howe

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    Member Array Hawkerdriver's Avatar
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    Jon- Not a "novel"..Thanks for taking the time.Lots of info in there,and by no means am I a SWAT guy..Fair with combat pistol,but haven't had that much experience with long guns...I will try to put Austin's suggestion into play and see what happens..I have a hard time doubting my gunsmith's workmanship in this case,as he is one of the best and most concientious around here..I may take it by there today though.

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    Member Array Hawkerdriver's Avatar
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    Austin- Heres some more answers to your last questions..
    1.Using large aperture.
    2.Familiar with peeps,but hard on my eyes aquireing front sight post.I'm 57..
    3.Don't have a sling for this weapon yet. Just haven't picked one up yet.I am familiar with the proper use of slings tho.
    4.Using the knob,it will go 50 clicks either side.I have returned it to center posit.
    I'm thinking iron problem was my cheek posit,as I was not able to get totally comfortable in prone that day.I will be using a bench next time.
    5.Barrel length is 16" I believe. (Original equipment)That's not counting the muzzle break.
    6.Elevation is not an option with this MBUS model.It didn't seem to be a problem at all from 50 yds tho.

    Thanks again..HD

  14. #14
    VIP Member Array jonconsiglio's Avatar
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    Just shot it with irons and that'll tell you if the work done is solid or not.

    Then, we start narrowing it down by process of elimination. I'd be happy to give you my number so you can call me from the range. Done it for a couple guys on here and the problem was always resolved before they left...

    Jon
    Proven combat techniques may not be flashy and may require a bit more physical effort on the part of the shooter. Further, they may not win competition matches, but they will help ensure your survival in a shooting or gunfight on the street. ~Paul Howe

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    VIP Member Array aus71383's Avatar
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    Quote Originally Posted by Hawkerdriver View Post
    Austin- Heres some more answers to your last questions..
    1.Using large aperture.
    2.Familiar with peeps,but hard on my eyes aquireing front sight post.I'm 57..
    3.Don't have a sling for this weapon yet. Just haven't picked one up yet.I am familiar with the proper use of slings tho.
    4.Using the knob,it will go 50 clicks either side.I have returned it to center posit.
    I'm thinking iron problem was my cheek posit,as I was not able to get totally comfortable in prone that day.I will be using a bench next time.
    5.Barrel length is 16" I believe. (Original equipment)That's not counting the muzzle break.
    6.Elevation is not an option with this MBUS model.It didn't seem to be a problem at all from 50 yds tho.

    Thanks again..HD
    1. You want to use the small aperture for sighting the gun in. You'll get a much better sight picture that way. With the AR-15 you want the tip of your nose touching the charging handle. The large aperture is "technically" for 0-200 yds, but in practice it is for low light or fast shooting at close range.
    2. If you get your eye up close to the peep (small aperture) sight, it will help your eye focus on the front sight - gives you little else to look at.
    3. Good - that's one thing we can rule out. A sling can help with accuracy from different shooting positions, but if you have it very tight it can change the point of impact.
    4. Centered is a perfect starting point. Small aperture.
    5. 16" barrel without an F marked front sight might mean that you will have your front quite a ways up in order to have it zeroed. Not a huge deal but good to know in advance so you don't think something is wrong.
    6. You will be making any necessary elevation adjustments by using the front sight. If you look down on it from above, you'll notice that it says "UP" and has an arrow. This will move the point of impact up. The front sight will actually go down. There is a little "nub" with a spring and detent that needs to get pushed down to allow front sight elevation adjustments. In the military we just used the tip of a bullet. A 16d nail would probably work better. You push it down, get the turning started....then push it around until it clicks into place. Each click of front sight adjustment will raise/lower the point of impact about 1.5 MOA (depending on barrel length) - so if you need to go 1.5 inches at 50 yds you want 2 clicks. 3 inches = 4 clicks. and so on...

    Good luck - you'll get it figured out.

    Irons = small aperture

    Blue Locktite and secure those things well. Be sure to push forward when tightening.

    Austin

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