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side mount sight rail is off center...

side mount horizontal drift right hand twist parallax

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#1 yard



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Posted 14 March 2016 - 12:46 PM

I have a 7.62x39 and added the side mount rail and an open reflex type sight.


The top rail is obviously off-center to the left.  I've sighted it in at 50 yds and it holds true at 100 yds too.  I expect some sort of parallax to cause the point of impact to eventually move further and further to the left as distances grow but in the distances that I've shot, it doesn't.  I also expect the opposite as distances are nearer, but that hasn't been obvious either even down to 50ft.  My question:


The rifling is right-hand twist which will cause a rightward horizontal drift.  Does the off-center nature of the rail actually help compensate for the horizontal drift like long-ranger's have a 20MOA downward angle that helps compensate for vertical drop?


My initial belief is that even though the off-center is around 3/8th of an inch, the difference is just not enough to be noticed within the functional limits of the rifle.  I'd love to try it at around 300yds or so, but those ranges just aren't available around here (begging the question, WHO CARES?) but I'm really curious whether this has made a difference for anyone.



#2 mancat


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Posted 14 March 2016 - 02:17 PM

Welcome to AKs.. Not all AK mounts are designed to sit center to bore, unfortunately. Many are biased towards the left.


Most US-made mounts are designed to sit center, but this is never guaranteed, especially if the mount on the receiver itself is slightly out of spec. I have one Bulgarian rail that is slightly thinner than normal and this puts every mount slightly offside to the right of the bore.


The majority of Soviet type optics are left offset. Would they still hit POA out to 1000yd with that offset? Maybe not, I don't know. Within the typical 400m ranges that most of those optics are calibrated for, it doesn't seem to be an issue.

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#3 yard



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Posted 14 March 2016 - 04:53 PM

Thanks mancat.  It's nice to hear from someone with some understanding and experience on the issue.


Thankfully, I have other options for distances out to and beyond 1000yds !


Happy shooting.

#4 imarangemaster


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Posted 14 March 2016 - 05:42 PM

I have yet to find a side mount of ANY kind that centers over the bore! LOL

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#5 G O B


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Posted 15 March 2016 - 11:55 AM

Parallel is more important than centered over the bore!

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#6 Horse


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Posted 29 April 2017 - 11:58 AM

The RS Regulate side mounts have gross windage adjustment in the design to allow perfect centering.

#7 HB of CJ

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Posted 30 April 2017 - 05:47 PM

Both of our Saiga factory left side receiver scope mount rails were way off.  WAY OFF.  The scope was looking at the moon and the barrel was pointed at the ground.  Almost that bad.  Way off both up and down and side to side. 




Fun, easy and doable.  We ground down the factory rivets and punched them out, removing the rail.  Then we calculated how much shim stock of what thickness would be needed to physically shim the factory side rail sosss the scope would almost, if not perfectly, be dead center with the aperture, (cross hairs, dot) in the exact center position zeroed at 100yds.


Zeroed with the cross hair adjustments dead centered.


Then both end holes of the rail were elongated up and down.  THE MIDDLE HOLE LEFT ALONE.  The shim stock we cut of of non expensive automotive valve adjustment shims from a cheap tool bought at the parts store.  The shims were cut to fit around the new short bolts.  We just used Blue Loctite and lock washers on the replacement short Allen head screws.


Allen heads on the outside.  Short bolts, lock washers and hex nuts on the inside.  Threads ground down flush.  Seems to clear the guts.


Tammy my smart granddaughter calculated the exact shim thickness in her head.  The factory rail was about 40" off high and about 24" off to the right at 100 yards.  The correct thickness was easily calculated.  I forgot what the exact thickness it was.  It physically moved the rail.  A fun, easy if somewhat time consuming job to do.  All in one afternoon.  Drimmal, (sp) tool.  Shim stock.  Blue Loctite.  Allen head wrench.  Small box wrench.  Three (3) short Allen head screws, lock washers and hex nuts.


Hope this helps.  But ... then both EoTecks got sent back for a refund.  Go figure.  smile.png

Edited by HB of CJ, 01 May 2017 - 10:26 AM.

Also tagged with one or more of these keywords: side mount, horizontal drift, right hand twist, parallax

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