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Discussion Starter · #1 ·
I mounted a Leupold Mark 4, 1.5 - 8 X with an SPR reticle on my M1A Bush Rifle (18 inch barrel). I used an ARMS # 18 mount and a set of ARMS # 22 low rings. I attempted to zero the rifle/ scope at 25 yards. During the proccess I found that I was shooting very high, about 20 inches high so I adjusted the elevation on the scope that brought the rounds down a couple of inches but I ran out of adjustment on the scope. So even with the scope adjustment bottomed out my rounds still hit about 15 inches hight at 25 yards! What do you guys think?
 

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I think your receiver scope mount interface is having issues with the ARMS mount...

You can try to rework the mount or get a Sadlak or SEI mount that allows for these tolerance issues.
 

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Discussion Starter · #3 ·
You could be right, but the mount appears to be paralel with the bore but I don't know for sure.
 

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Level the barrel and then check level on the mount. You'll need a short level like a string level to do it.

Is the mount tight to the clip guide?
 

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Discussion Starter · #5 ·
Thats what I did. I checked the barrel and mount with a small level and they were the level in relation to one another. The mount and rings are rock solid, no movement. One thing, I did get the scope used but in like new condition. I think its the the scope...
 

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Scope

I found when scoping these rigs you need some forward cant to the scope. Mine is sighted in at 300yds and I use a lower front ring set-up. Then I use mil dots for shots that are 200 and 100...works lovely......shim the dovetail with a filler in the stripper clip guide slot and run back set screw down tight, then just bottom out the front set screw, that will give you some cant on the mount but not much because of the splineway on the receiver.
 

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rip, he's got downward cant, too much though...

As a test, swap ring positions front to back and see if it changes. If not it's the mount or scope. If the mount is level as you say then it has to be the scope. Leupold does have a great warranty service...
 

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I have had the same issue with my #18, but I ran out of windage adjustment. Don`t try to shim the mount, it should be installed absolutely tension free. Find someone to swap the scope with and see if the problem is solved with a different scope/ring combo. If not, try a different mount. shiet happens.
Wolf
 

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Before you send the scope back to Leupold, I've got a few questions. How much adjustment did you make before the scope maxed out? According to Leupold, that scope should have 120 MOA of total adjustment. That means 60 MOA each of left and right windage, and 60 MOA each of up and down elevation. Now that spec is after the scope has been optically centered. So since you said you bought that scope used, I'm guessing it wasn't optically centered anymore. Is the scope bent? If a scope is bent you will lose adjustment. It depends on how bad it is bent though. If everything checks out on your end, you may be right and suspect the scope has a problem. If it does have a problem, I would guess it would be a tight guide tube pivot, or a flat bias spring.
 

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mount

I have had the same issue with my #18, but I ran out of windage adjustment. Don`t try to shim the mount, it should be installed absolutely tension free. Find someone to swap the scope with and see if the problem is solved with a different scope/ring combo. If not, try a different mount. shiet happens.
Wolf
What do you mean don't try and shim the mount ? I used a Bomar cut 1911 rear sight base and custom filed it to fit the stripper clip guide...works fine...guaranteed to outshoot just about anyone......except maybe 338 Lapua's....My zero remains.....

....No Expert,... how can he have too much forward cant and be shooting high ?
 

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....No Expert,... how can he have too much forward cant and be shooting high ?
Geometry... The more forward cant you have, the higher the muzzle comes up to level the scope on your target. Same principal as the rear sight. Your rear sight comes up increasing the sight's forward cant making the muzzle point up to level the line of sight. Too much and you shoot high.

If he had too much rearward cant he'd be shooting low.
 

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I have always optically centered a used scope before mounting, then I always try to get it as close to zero before making adjustments with the knobs. I have heard some guys say they crank the elevation down from factory center and then try to get it zeroed with different bases etc....they advised this gives them more adjustment for further distances
 

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cant

Geometry... The more forward cant you have, the higher the muzzle comes up to level the scope on your target. Same principal as the rear sight. Your rear sight comes up increasing the sight's forward cant making the muzzle point up to level the line of sight. Too much and you shoot high.

If he had too much rearward cant he'd be shooting low.
D'OH.....uhhh, ok...thanks,..still half asleepGI8
 

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I have always optically centered a used scope before mounting, then I always try to get it as close to zero before making adjustments with the knobs. I have heard some guys say they crank the elevation down from factory center and then try to get it zeroed with different bases etc....they advised this gives them more adjustment for further distances
I would agree with changing the elevation to a point. As long as you are not completely maxing out elevation and then zeroing. Maxing out a scope is hard on them and they will not hold zero for long left that way. As far as zeroing the scope to the rifle, Burris Signature rings work wonders for that. And the inserts don't leave ring marks or stress the scope when torquing into place. Then you can make your fine adjustments with the scope and still have useable adjustments. Also the closer to center a scope is, the better the image and function.
 

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What do you mean don't try and shim the mount ? I used a Bomar cut 1911 rear sight base and custom filed it to fit the stripper clip guide...works fine...guaranteed to outshoot just about anyone......except maybe 338 Lapua's....My zero remains.....
If shimming means to bend the mount with a shim on one side it would put tension on the mount and the receiver. No good idea.
Wolf
 

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I mounted a Leupold Mark 4, 1.5 - 8 X with an SPR reticle on my M1A Bush Rifle (18 inch barrel). I used an ARMS # 18 mount and a set of ARMS # 22 low rings. I attempted to zero the rifle/ scope at 25 yards. During the proccess I found that I was shooting very high, about 20 inches high so I adjusted the elevation on the scope that brought the rounds down a couple of inches but I ran out of adjustment on the scope. So even with the scope adjustment bottomed out my rounds still hit about 15 inches hight at 25 yards! What do you guys think?
Beginning at the beginning, when the ARMS #18 was first installed, did the angled rear end of the mount rest on the stripper clip guide dovetail or was there some daylight? For the mount's horizontal and vertical keys to sit squarely in the receiver's corresponding grooves, there has to be a bit of space in back; what ARMS calls the "circular spacer" is then used to bridge the gap. If the back end of the mount rides up on the dovetail, you'll get exactly the kind of zeroing problems you're having, as I did on two out of three such installations. The only solution I've found that works, other than using Burris Signature rings as JMGlasgow suggests, is to carefully grind back that angle on the mount until there's daylight.

The other thing to consider is that I believe the horizontal and vertical scope adjustments interact in the sense that you can't use both extremes at once; i.e., a substantial windage adjustment will reduce the range of elevation adjustment you actually have, no matter what the specs say.
 

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When I first began my ARMS 18 mount, the front screw tension pad was way high. It would hold the front of the rail high like what's described. Adjust that pad so it does not touch the receiver when the mount is torqued down. Then check your zero. If you get your zero back, then run that front pad down for just a bit of tension after torqing the side screw. Interesting... keep us posted.
 
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The OP didn't return to provide his resolution?


I just switched scope rings (from Mark IV medium to high) on my Leupold Mark IV and now it too won't zero where it was zero'd before. I did notice one of the high pieces has a manufacturing flaw as it doesn't mate correctly with its scope ring piece.
 

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