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Compatibility of 20MOA Rail

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Marine24 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marine24 Quote  Post ReplyReply Direct Link To This Post Topic: Compatibility of 20MOA Rail
    Posted: December/02/2020 at 20:59
It has been awhile since I posted but wanted to share an odd experience I'm working through.

Had a 338-06 rifle built using a Big Horn Arms Origin action with a 20MOA rail and one of Mark Chanlynn's barrels.  Mark put the rifle together for me.  Stock is a B&C Medalist and it is topped with a Leupold VX6 HD 3-18x44.

Pretty straightforward build but first attempt to sight it in had the round hitting 13" high at 100 yards above point of aim.  Elevation was bottomed out with no adjustment available.

Thought it was me, so I remounted the scope and torqued the rings and clamps to appropriate in/lbs.  Tried sighting it in again and behavior remained the same.  Mounted a different scope and ring combination on the rifle and still shot high.  

Big Horn Arms/Zermatt was nice enough to send me a new 20MOA rail.  Unfortunately the Origin action is only comes with a 20MOA rail.  Received it today and installed it along with the scope on the rifle.  Third time wasn't a charm.  Behavior remained the same with shots impacting a foot high at 100 yards from point of aim.  It shoots 5/8" to 3/4" groups with a variety of 185 and 210gr bullets, but high.

According to Ray at Big Horn Arms, the next options is to install either two front Remington 700 picatinny bases or two front Talley scope mounts.  The hole spacing only works with the front bases or scope mounts.  I reached out to Talley to see if they would sell me two front scope mounts.  If not, I'll get a couple sets from Brownells and toss the rears.

Other odd behavior on the rifle is that the hinged floorplate will spring open after firing the shot.  Doesn't happen all the time, but about every three or four rounds.  Not sure if they are related.  I'm confident I'm not hitting the release when the rifle recoils.

I'm going to remount the stock to barreled action to see if that helps the floorplate behavior and check the inletting on the stock.  There isn't the typical "play" in the hinged floor plate

I understand there are some combinations of calibers and optics that aren't compatible with a 20MOA rail, but not sure how one would determine that.

Would welcome your ideas on other areas to check if the scope mounts don't resolve the issue.

Mike


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tejas View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tejas Quote  Post ReplyReply Direct Link To This Post Posted: December/02/2020 at 22:47
You could try some 20 MOA rings. I think Burris makes some. The have inserts for different scope elevations. You’d have to mount them opposite of how they are designed to work of course. 
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Marine24 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marine24 Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 05:58
This is a hunting rifle with most shots inside of 300 yards so additional elevation isn't necessary.  It just how the Origin action came.  First time I've run in to a scenario where having it was a negative.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kickboxer Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 07:59
Mike, you might try contacting Near Manufacturing.  Richard Near has done some custom work for me in the past.  You might be able to send him your rail and have one made at 0MOA with that hole pattern.  He made a custom rail for my Champlin .378 Weatherby Magnum that works perfectly (the Champlin did not come with a rail).  

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Sgt. D View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sgt. D Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 08:36
Apparently they simply don't offer a standard rail. And it says the rail is "pinned" so I can't offer any easy swap options not knowing just how they are pinned. But that is where I would focus to start with. Evidently Big Horn offered no real help in solving the problem. You've tried a different scope so we should rule out the first scope being the problem. Unless you try that scope on another rifle and it has the same problem. These are things you shouldn't have to do when dealing with a big name company or builder. But here you are. I have to start with kinda elementary basics since I don't know you level of experience so take no offense as you may well exceed my own experience. If the barrel is not free floated it could cause point of impact shifts and even poor grouping but shouldn't cause you to have to max the elevation in the scope. If by chance you are resting the barrel on your bench or shooting rest it could easily cause POI to be up to a foot high or more, consistently. If the barrel is floated but has a load bump at the end of the forearm it could cause a similar issue though that would be extremely rare. If you have access to a machine shop or gunsmith you could get a rail blank (just do a search for weaver rail blank) and contour it to match the receiver. Then pull or drill the pins from the receiver, drill, tap and then drill the rail to match. That would give you a standard flat rail that "might" solve the problem.
But the thing I see is a 20 moa rail should not require maxing the elevation under normal circumstances. I've seen this a few times before on some Remington rifles and it always ended up being the scope.
 
Sucks when a prize toy lets us down. The Burris ring suggestion could give you what you need. You just have to decide where you want to start $$.
Good Luck with it!!
 
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Sgt. D View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sgt. D Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 09:04
(Quote
According to Ray at Big Horn Arms, the next options is to install either two front Remington 700 picatinny bases or two front Talley scope mounts.  The hole spacing only works with the front bases or scope mounts.  I reached out to Talley to see if they would sell me two front scope mounts.  If not, I'll get a couple sets from Brownells and toss the rears.
Quote)
 
That suggests that the rail is not pinned. Might better check before you buy anything. You may to have the receiver drilled and tapped.....
 
 
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supertool73 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote supertool73 Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 09:09
sometimes pins are just little metal pins that are not fixed to either base or action.  My Tikka CTR was that way, just to keep the base more rigid during recoil.   


Edited by supertool73 - December/03/2020 at 11:21
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tejas View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tejas Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 10:04
This is copy/pasted from a competitors website so I’m
Not going to post the link. It gives a better explanation of Burris Signature Series Rings/Inserts. SWFA probably sells them.


Overview

These offset inserts work only in Burris Signature Rings. One insert half is slightly thicker and the other slightly thinner than standard. Swapping the standard inserts with a pair of offset inserts will move the point of impact approximately 5" at 100 yards for the .005 inserts, 10" for the .010 and 20" for the .020. This will allow a gun to be sighted in that cannot be zeroed with the available windage and elevation adjustments in the scope. For serious shooters, the optional offset inserts allow a scope to be brought almost to complete zero, then using the windage and elevation adjustments only for the final, fine adjustment. This keeps the erector tube centered in the scope for improved scope clarity and performance. Includes "zero" inserts, other Pos-Align inserts can be purchased separately. 

Notes: 

  • Contains 6 insert halves, enough for three rings (one .005 offset, one .010 offset, one .020 offset)
  • Synthetic inserts for 'Signature' rings only
  • Inserts have the center opening offset by the amount of distance shown in the description. For example, .005" offset inserts will move the scope tube .005" toward the thinner of the two inserts. The inserts can be used to move the scope tube in the front ring, the rear ring or both rings. The inserts may also be used in any combination as long as the matched halves stay together. A set of .005" inserts may be used in the front ring and .010" inserts in the rear or whatever combination is needed. 
  • If the inserts are used to move the front of the scope tube to the right, the point of impact at 100 yards will move to the left approximately 5 inches. If the scope tube is moved in the rear ring to the right, the point of impact will move to the right.
  • Inserts can be used to move the scope tube in any direction needed for windage and/or elevation.
  • This kit has 1 each of +/- .005", +/- .010", and +/- .020" inserts

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Marine24 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marine24 Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 12:23
The rail is pinned and action has additional holes drilled and tap to accommodate the pins as you can see in the picture.  You can also see the hold spacing for the rail screws.

I'd thought about just using a different rail, but the spacing messed up that idea.


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Marine24 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marine24 Quote  Post ReplyReply Direct Link To This Post Posted: December/03/2020 at 12:48
Talley is willing to sell me two front mounts, so those are on its way.  The Burris rings or possibly going with Kickboxer's smith might be Plan B.

More to follow as this drama unfolds.
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Marine24 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marine24 Quote  Post ReplyReply Direct Link To This Post Posted: December/14/2020 at 21:09
Saga continues.  Talley's two front mounts worked fine but action is so long, the VX6 won't fit.  Either the mount hits the forward bell or the rear base interferes with the magnification ring.  If I had gone with Medium rings, may have worked.  Scopemounts are mounted with the bases pointed outboard.  Spacing is 5 1/4" from the outside edges of the rings.

Had a Leupold 2.5-10x45 LPS that fit.  It will be fine to get out to the range and ensure the Scopemounts are the fix.  It isn't a bad scope and may be permanent.

First time I've had a problem getting a scope to mount on an action, even a long action like the Origin.  Not sure what spec I would even look at to see if a scope would fit on those mounts.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Scrumbag Quote  Post ReplyReply Direct Link To This Post Posted: December/15/2020 at 12:32
Are you wedded to that scope? Do you have something with more elevation travel

Rails are there to get you elevation to shoot a long way so I guess the real answer is you can't depress your scope enough to zero at 100...
Was sure I had a point when I started this post...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tahqua Quote  Post ReplyReply Direct Link To This Post Posted: December/15/2020 at 13:59
I had the same problem with my 6.5 CM APO M700. The rail is a 20 moa and the scope is a Steiner P4xi 4-16 x 56. I couldn't get a 100 yard zero. I checked the base and ring torques and started over. I figured with 30 mils vertical adjustment I would be good for a 100 yd zero with the 20 moa rail. I did eventually figure it out but I was actually 15.4 mils below mechanical center when zeroed at 100, not good. To be zeroed close to mechanical center vertically I went PBR for zero and will go from there for different ranges.
Doug
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Marine24 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marine24 Quote  Post ReplyReply Direct Link To This Post Posted: December/15/2020 at 15:03
I like the VX6 3-18X on my hunting rifles.  More top end than I typically need since I keep shots inside of MPBR, but is useful when working up a load.  Unless I pull the Scopemounts and attach a two piece picatinny rail, using the V6 isn't an option.  The Leupold LPS will do the job for now.  




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