Rifle Scopes Larue OBR 7.62 and Hensdoldt SSP-P Mounting Issue

[GBMaryland]

So,

I've got a Larue OBR 7.62 (aka really nice AR-10) with the standard monorail that goes from the A3 type upper reciever across the handguard.

I've been able to save up the cash to pickup a PM II and it occured to be that the Hensholdt SSG-P could work well on that rifle. (I'm redistributing optics...)

When I go to mount the scope on the OBR, it's very obvious that it's loose! Now, I don't recall the being the case on the previous rifle it was mounted to...

Anyone know if the OBR adheres to the standards for the picatinny rail system from the military?

It's really odd... the scope recoil lug clearly is narrower than the OBR mono rail grooves.

Help!

(There is nothing in the Hensholdt manual for the 3-12x56 SSG-P with the integrated mount for the G22.)

 

[poison123]

Marks Stuff is Texas Spec....which is evidently better than Mil-Spec......

 

[GBMaryland]

Well,

I'll have to pull out an AI and the TRG Rails from Richard Near and see what the over all specs are. I'm perfectly willing to have a new lug cut if they are removable.

 

[Falsecrack]

I've mated both my S&B 5-25 w/NEAR Alphamount and my USO SN3 3.2-17 w/Spuhr with zero issues.

 

[GBMaryland]

The SSG-P is the variant with the integrated clamp mount.

It doesn't use rings....

 

[ZombieMonkey]

You try and throw any other scopes on the OBR yet? I'd be curious to see where the issue is. Never had an out of spec part from Larue, though I'm sure it is well within the realm of possibilities. I would think it would have been caught at the factory with the rifle since they do mount a scope and test fire them before they leave. I am curious what the cause of the issue happens to be. Keep us updated.

 

[CS95]

It's really odd... the scope recoil lug clearly is narrower than the OBR mono rail grooves.

Help!

Are you saying that the scope is loose when you have the mount tightened up or are you just talking about how the recoil lug fits in the receiver?

 

[GBMaryland]

It appears to be related to both.

1) The scope IS loose on the OBR monorail...

2) The groove on the OBR is to wide, and that does allow the scope forward<>rear movement.

I mounted it on:

An AR-57 upper... no moment
TRG-42 - Accessory Rail - No movement
Larue Remington 700 Rail - moves
Larue 7.62 OBR monolithic 20MOA rail - moves

So, now for the interesting part:

The specification is .206 inches for a groove in a Picatinny Rail.

The AR-57 was .2075 very close to .206.

The TRG-42 accessory rail was .2060 - dead on.

[Richard Near made me the mount for my scope, which I didn't feel like taking off.]

The Larue OBR Rail was .2105, which, if you take the general spec of .206... the Larue is much larger.

The recoil lug on the Hensholdt is .1900 inches exactly for the SSG-P scope with the integrated mount / locking mechanism.

The Larue LT111 is .1965, which is why it works so when on an OBR.

Soooo.... the issue is the tolerance on the Larue rail, not the scope, which appears to mount without issue on rails that are exactly MilSpec.

It would seem to me that Larue designed the OBR with their quick mounts in mind, and the largest possible tolerances.

So, unless I can get a replacement recoil lug, I'll have to use this on rifle with an in-spec rail.

 

[poison123]

It appears to be related to both.

1) The scope IS loose on the OBR monorail...

2) The groove on the OBR is to wide, and that does allow the scope forward<>rear movement.

I mounted it on:

An AR-57 upper... no moment
TRG-42 - Accessory Rail - No movement
Larue Remington 700 Rail - moves
Larue 7.62 OBR monolithic 20MOA rail - moves

So, now for the interesting part:

The specification is .206 inches for a groove in a Picatinny Rail.

The AR-57 was .2075 very close to .206.

The TRG-42 accessory rail was .2060 - dead on.

[Richard Near made me the mount for my scope, which I didn't feel like taking off.]

The Larue OBR Rail was .2105, which, if you take the general spec of .206... the Larue is much larger.

The recoil lug on the Hensholdt is .1900 inches exactly for the SSG-P scope with the integrated mount / locking mechanism.

The Larue LT111 is .1965, which is why it works so when on an OBR.

Soooo.... the issue is the tolerance on the Larue rail, not the scope, which appears to mount without issue on rails that are exactly MilSpec.

It would seem to me that Larue designed the OBR with their quick mounts in mind, and the largest possible tolerances.

So, unless I can get a replacement recoil lug, I'll have to use this on rifle with an in-spec rail.

Told ya....Texas Spec.

 

[GBMaryland]

Yeah, clearly there is some sort of an idea that the rail will be used for compression fitting without a recoil lug that is intended to fill that gap.

On my European rails, and stuff with tight tolerances... the scope appears to mount and not move at all. (The thing is a beast.) Just not on the OBR...

What IS interesting that that my Larue 556 upper has tighter specs:

Rail grove is .2020
A3 grove is .0207 (which will work)
Rail rung is .1900
A3 rung is .1870

So the A3 part of a 556 Stealth upper should work without issue... I may end putting it on that 556 rifle.

Such a bummer about the Larue OBR 7,62 being that much toward that is likely either out of spec or just inside that maximum spec. I'll call em...

 

[GBMaryland]

Told ya....Texas Spec.

Well, everything IS supposed to be bigger in Texas.

 

[GBMaryland]

I picked up a Remington 700 Short Action rails from:

Warne (0 MOA)
Night Force (20 MOA)
Badger (20 MOA)

Plus I have the Larue 20 MOA I spoke about and then the mono-rail on the OBR.

The Hensholdt SSGP has no problems with the Warne or the Badger. Didn't try the Night Force, as it appears to be identical to the Badger.

SOOOOO..... this tells me that the Larue bases are different, be it slot size, rail external dimensions, or who knows what.

What I can tell you is the an SSG-P will not mount properly to a Larue rail, either on the OBR or the 20 MOA one made for the Remington 700 SA.

I did call them, and I did ask if they'd make me an OBR mono-rail with slightly altered dimensions... and that absolutely went no where. (I really wasn't concerned about cost...)

Assuming they write their own programs using Solid Works, or something like it... it's possible for a reasonable price ($1000.00?).

In this case, btw, it's likely that the external proportions are actually SMALLER in Texas. I has to be related to the clamping mechanism's ability to grab the sloped edges of the rail.

 

[Thebelly]

Ok, so as I see it, the LaRue rail meets the spec found here (which, near as I can tell is the reals deal): Picantinny Rail Specifications

The weird thing here is that the specification is that the slots on the top of the rail are designed to have a bit of wiggle, as evidenced by the .206" - +.008" marking. I'm interpreting this as the slots can be as small as .206" but as large as .214". This would give manufacturers the maximum opportunity to be 'within spec'.


A smart company will aim dead center of that: .206 + .004" = .210". Again this provides the opportunity to have lots of accessories fit.

If your LaRue is measuring at .2105", there may be some wiggle, front to back. I think that being 1/2 of 1/1000th of an inch might be forgiveable...acceptable, even.


As it applies to the mounts, if the bottom 'recoil' lug on the LaRue mount is smaller than the slot on the rail, it will fit! It just might be designed that way.

If there is wiggle forward and back, that means that it fits. There are ways to attach a mount to a rail and have it not slip. Understanding recoil forces is your friend.

 

[mkollman74]

Ok, so as I see it, the LaRue rail meets the spec found here (which, near as I can tell is the reals deal): Picantinny Rail Specifications

The weird thing here is that the specification is that the slots on the top of the rail are designed to have a bit of wiggle, as evidenced by the .206" - +.008" marking. I'm interpreting this as the slots can be as small as .206" but as large as .214". This would give manufacturers the maximum opportunity to be 'within spec'.


A smart company will aim dead center of that: .206 + .004" = .210". Again this provides the opportunity to have lots of accessories fit.

If your LaRue is measuring at .2105", there may be some wiggle, front to back. I think that being 1/2 of 1/1000th of an inch might be forgiveable...acceptable, even.


As it applies to the mounts, if the bottom 'recoil' lug on the LaRue mount is smaller than the slot on the rail, it will fit! It just might be designed that way.

If there is wiggle forward and back, that means that it fits. There are ways to attach a mount to a rail and have it not slip. Understanding recoil forces is your friend.

Agree with this. ^^^^^^ HINT: recoil only occurs in one direction...

 

[livetohunt]

My SSG-P mounts perfect on my OBR.I would say adjust the small silver nut on the side of the scope and that should adjust the tension on the clamp.
I would take mine off and check but whitetail season is still open.

 

[Thebelly]

As far as the 'how to' of mounting a scope and rings, here's a pretty good instructional video that highlights the fact that this forward and rearward movement is normal and how to mount accordingly.

"Budget Precision" Pt.2 - TPS Ring and Scope Mounting, Remington 700 - YouTube

 

[GBMaryland]

Folks,

I appreciate the input... here are the facts:

- The OBR and Remington 700 rail that I have from Larue literally allows the scope when attached to the rail to move forward and backward.

- The adjustment screw on the SSG-P does not affect the above at all (I wish to hell it did)

- The SSG-P has a integrated mount (for those that did not notice this)

- A Badger Ordnance Remington 700 rail allows the scope to be mounted flawlessly without any movement

Now, for anyone indicating that movement is "normal," well, I don't think that SLAPPING forward or rearward is normal. PERIOD. You can mount the scope, take your pinky, and move it forward and backward - it's THAT loose.

There is no secret here... the Larue rail systems are not the same in some aspect as the other brands.

This totally sucks as the SSG-P is perfect for an AR type platform... not so much for a bolt action rifle (due to height). ...and it's an awesome piece of glass.

However, with the integrated mount you have limited options if it doesn't firmly mount to the rail.

If someone's an expert with the SSG-P scope's adjustment features, well, I'd love to hear what you have to say.



I did contact Zeiss, and they send me to someone in the mid-Atlantic states, and he didn't get back to me.

 

[ZombieMonkey]

If it can move backwards when actually tightened down...you're doing it wrong.

I am sorry, but there is no other way around it...

 

[scharfschutze762]

There is a way to tighten it. And yes the Larue rails are not ml spec because the elcans were loose on them and there answer is to run a different optic set up. GBM contact finnaccuracy and he will square you away on how to adjust it.

 

[GBMaryland]

FYI: This was the final result, and I opted to post it in a new thread is case anyone has this issue in the future:

http://www.snipershide.com/shooting...-clamping-scope-adjusting-clamp-pressure.html

Basically, the Larue rail IS smaller, and because it's not in the middle of the spec, I needed to add a 1mm spacer to the clamping mechanism. Plane and simple, there are not NATO spec... Which means they are close to not being DoD spec either...