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Center crosshair on my scope

This is a discussion on Center crosshair on my scope within the Optics forums, part of the Gun Forum category; Need advice on how to center the crosshair on my scope. I mounted a Khales ZF 84 scope on my M1a using the SEI mount. ...


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Old January 20th, 2009, 06:52 PM   #1
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Center crosshair on my scope

Need advice on how to center the crosshair on my scope. I mounted a Khales ZF 84 scope on my M1a using the SEI mount. Somehow my crosshair is zero'd at the top right center. I cannot get the crosshair to align in the center.... Any advice will be greatly appreciated.

Tom

I

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Old January 21st, 2009, 09:28 AM   #2
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Need advice on how to center the crosshair on my scope. I mounted a Khales ZF 84 scope on my M1a using the SEI mount. Somehow my crosshair is zero'd at the top right center. I cannot get the crosshair to align in the center.... Any advice will be greatly appreciated.

Tom
Is what you're saying that instead of the vertical part of the reticle going from 12 o'clock to 6 o'clock and the horizontal going between 3 o'clock and 9 o'clock with the two meeting in the center of the visual field when you look straight through the scope, that the crossing point is up near, say, 2 o'clock at the edge of the visual field? If so, was it that way looking through the scope before you installed it on your rifle, right out of the box?...

I'd started to discuss how a reticle could get screwed up, but did some research on your scope since I've never heard of it. I found the following at http://www.snipercountry.com/roster/...2001_31_31.htm, specifically "...The main difference being that in the ZF84 the reticle is not centred, ie, when you adjust for elevation or windage, the damn reticle moves inside your scope,( so at lets say 800m with a 15mph wind from 90 deg right to left, your reticle would be in the far top left of your field of view through the scope) I personaly dont like this, but some do, but it tends to restrict field of view around your target and is basicaly old technology, although Gerhardt still manufacture scopes in this fashion, claiming that the fact that the reticle moves around lets you know when your windage and elevation are employed, so you don't make the mistake of leaving the scope elevated or windaged when you shoot at another range, ie it gives you a reminder to reset your cams or turrets back to 0.Both where available with and without turrets..."

http://www.kahlesoptik.com/index.php...1&kategorie3=0 has an instruction manual for the scope and while it doesn't really explain it that I can see, it does confirm that your scope is really supposed to do that.

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Old January 21st, 2009, 10:49 AM   #3
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Try this one- Hold the front of the scope flat against a mirror. Look through the scope and you'll see two sets of crosshairs, the real ones and the reflection. Twiddle the knobs until the reflected crosshairs line up with the real ones and look like one set- the crosshairs will be centered in the scope at that point.

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Old January 21st, 2009, 02:23 PM   #4
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Before the scope was mounted, the crosshair was centered in the middle of the rectical. I could adjust both windage and elevation with no problem as I can see the rectical move as I clicked on the dial. After I mounted the scope, let say, if I aim a target at 100yds on a flat bench, I will need to click the dial moving the crosshiar from the center rectical to the upper top right (10 o'clock across and 2 o'clock down) to have it aim on the target. There is not much I can do except maybe tinker with the mount.

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Old January 21st, 2009, 02:51 PM   #5
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Before the scope was mounted, the crosshair was centered in the middle of the rectical. I could adjust both windage and elevation with no problem as I can see the rectical move as I clicked on the dial. After I mounted the scope, let say, if I aim a target at 100yds on a flat bench, I will need to click the dial moving the crosshiar from the center rectical to the upper top right (10 o'clock across and 2 o'clock down) to have it aim on the target. There is not much I can do except maybe tinker with the mount.
I think you're headed in the right direction. If the mount is not in line with the barrel, windage and elevation adjustments are necessary to compensate beyond accounting for ballistics. On a normal scope, only the POI changes; on yours, the reticle actually moves. Reading through the installation instructions, the SEI mount doesn't appear to naturally align itself with the rifle bore; it needs to be adjusted, which is why you need to take the rear sight off to get the rifle level before you begin the installation. So tinkering with the mount would be the best place to start.

Another alternative is to check out Burris Signature rings. They offer offset inserts which allow you to position the scope within the rings to achieve a physical zero before you touch the windage and elevation knobs.

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Old January 21st, 2009, 03:16 PM   #6
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M1AallTheWay...Thanks for your advice and confirmation. I was afraid that was the scenario.

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Old January 21st, 2009, 06:37 PM   #7
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get a Sadlak mount

the back base has adj possibles

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Old January 25th, 2009, 06:20 PM   #8
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Center crosshair on my scope

When I first installed an A.R.M.S. #18 mount on my M1A SOCOM 16, I followed the accompanying instructions precisely. When done, it clearly looked misaligned, being down by the bow and yawed to port. I disassembled it and found that it just naturally fit into the receiver grooves that way as the screw was torqued. They say torque it up before setting the other two contact points (stripper clip mount dovetail and barrel ring support). Had to violate that rule and cycle all three adjustments along together in increments until the screw torque value was satisfied.

How to judge alignment as you go along? Here's the trick - -
Tape or hold a straight dowel along the top surface centerline of the mount (the #18 has a groove there, making it easy) and adjust the mount so the dowel passes evenly over the front sight when done. It is relatively easy to estimate vertical parallelism with the bore, but you can be picky and compare caliper measurements of rod position with respect to the centerline of the chamber (primer center of empty brass) and centerline of the bore at the muzzle, if you must. I just eyeballed mine and the on-scope adjustments had to be trimmed up only a minor amount when the scope was installed and targeted. I have found no lack of rigidity in the installed rig, in spite of the non-standard assembly procedure.

Because of all the fiddling to put it back, I don't intend to remove the mount, as the irons are usable if the scope and rings are removed as a unit.

It seems like some variation of the above might allow your mount to be pre-aligned parallel to the bore so scope adjustments are reasonably centered. I don't mind if my mount is a little twisted or strained to conform, as long as it stays that way.

Best regards - - - Smokey

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Old January 25th, 2009, 07:50 PM   #9
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When I first installed an A.R.M.S. #18 mount on my M1A SOCOM 16, I followed the accompanying instructions precisely. When done, it clearly looked misaligned, being down by the bow and yawed to port. I disassembled it and found that it just naturally fit into the receiver grooves that way as the screw was torqued. They say torque it up before setting the other two contact points (stripper clip mount dovetail and barrel ring support).
I ran into exactly the same problem you did with an ARMS #18 and a SOCOM 16. I never did get it to fit right but along the way learned what was wrong and ultimately got it to fit perfectly on an SAI Super Match. I found:

1-There was interference between the underside of the mount and the bulge on the receiver that the mounting hole is in the middle of. This caused the mount to twist horizontally. Some Dremeling on the mount's backside fixed that.

2-The horizontal distance between the mounting hole and the stripper clip guide dovetail was too short for the ARMS. Grinding the angled rear section of the mount so that it just cleared the dovetail cured the forward cant.

Alignment in both planes was established by tying a piece of thread to the front sight post and stretching it back through the rear sight and tying it off. When the thread was parallel to the top of mount and ran down the middle of the channel, the mount was straight. Once all the Dremeling was done, the ARMS sat straight naturally.

3-Since the hole in the receiver was too big for the ARMS bolt, the threads on the bolt repeatedly stripped. A Sadlak screw fit perfectly and, with a couple of washers (it's longer than the ARMS bolt) has held the mount in place ever since.

And when a new scope, with centered reticle, was installed, no windage adjustment was necessary and only a bit of elevation. Quite a difference from shooting over 40" high at 100 yards as it did before the surgery.

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Old January 26th, 2009, 07:57 AM   #10
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M1AallTheWay - - - Thanks for the mount-grinding fix. I am convinced my mount would respond to the same treatment. I took a close look at the touchpoints you mention and found the mount dovetail is about a half-millimeter off center leftwards in the dovetail groove. It also appears that my adjustment of the mount's front support post provided a very firm contact point instead of the mount fully imbedding in the receiver grooves, thereby holding the mount in alignment in spite of it all.

I am inclined to pull the mount off and apply your fix so I will have confidence that it will not some day shoot loose. Perhaps the Loctite will be kind to me (I used plenty) and let the parts come away clean. When my patience is at a high level, I will give it a go.

I like your use of string as an alignment guide; it should be much more easy to keep in place than a dowel or rod as I used.

Thanks, and best regards - - - Smokey

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Old January 26th, 2009, 10:40 AM   #11
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Originally Posted by Smokey Downs View Post
M1AallTheWay - - - Thanks for the mount-grinding fix. I am convinced my mount would respond to the same treatment. I took a close look at the touchpoints you mention and found the mount dovetail is about a half-millimeter off center leftwards in the dovetail groove. It also appears that my adjustment of the mount's front support post provided a very firm contact point instead of the mount fully imbedding in the receiver grooves, thereby holding the mount in alignment in spite of it all.

I am inclined to pull the mount off and apply your fix so I will have confidence that it will not some day shoot loose. Perhaps the Loctite will be kind to me (I used plenty) and let the parts come away clean. When my patience is at a high level, I will give it a go.

I like your use of string as an alignment guide; it should be much more easy to keep in place than a dowel or rod as I used.

Thanks, and best regards - - - Smokey
Glad to help. The ARMS #18 appears to be one of the very few mounts (the Bassett is another) which finds its position by virtue of its design; it doesn't have to be "adjusted." So the horizontal and vertical keys settling squarely into their respective receiver grooves is critical, and if the receiver isn't mil-spec, they probably won't without some help.

You appear to be one of the lucky ones who has a receiver drilled and tapped with the right size hole for the screw ARMS provides. I've tried that screw on four SAI receivers and on three, the hole was too big while the fourth fit perfectly. If you can torque yours to 100 in/lbs without stripping, you've got a very good fit indeed. For the rest of us, the Sadlak screw fits remarkably well. Sadlak also offers both a tap and a thread chaser to clean out that hole; with all that Loctite, the thread chaser might be a good idea.

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Old February 1st, 2009, 08:23 PM   #12
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Another alternative is to check out Burris Signature rings. They offer offset inserts which allow you to position the scope within the rings to achieve a physical zero before you touch the windage and elevation knobs.
You can also do this with "Alabama chrome" for almost free.

A couple months ago American Rifleman had an article on scope mounting. The author actually said that he'd used strips of duct tape to "shim" a scope ring. No kidding.

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Old February 3rd, 2009, 08:45 AM   #13
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You can also do this with "Alabama chrome" for almost free.

A couple months ago American Rifleman had an article on scope mounting. The author actually said that he'd used strips of duct tape to "shim" a scope ring. No kidding.
Tape between the rings and the scope tube is a good idea, and I use it myself to keep the rings from scratching the scope. But a pair of scope rings on a rail (or other attachment method) are really a long tube with the middle cut out which the actual scope tube has to fit inside of. If the parts of the scope ring "tube" aren't in alignment, or the scope tube has to be turned within them to get it pointing in a different direction, the outside of the scope tube won't line up with the inside flat area of the scope ring and the rings will try to twist the scope tube to get it to line up where they touch. That's what lapping is supposed to cure because it changes the direction of the ring's "tube," but in this case, we want the misalignment; we just don't want to bend the tube.

The Burris Signature rings have inserts which are thicker on one side than that other so that the scope can be offset, changing its natural aim point. But the inside of the ring is not flat; it's curved like a section of a sphere. The offsets have a matching curve on their outer surface so that as the scope finds its new position due to the insert offset, the inserts rotate inside the rings so that the "tube section" they're creating is following the direction of the scope tube, not the ring. It's easier to see at work than to describe. But it's something that plain tape can't do.

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