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Get rid of the lightening cuts in the rails. It will make the uppers easier to manufacturer and give better accessory compatibility.

Lighter trigger.

medium contour barrel 1/7 twist.
You nailed it. Lightning cut rails and Larue don't mix... that is bad. Medcon barrel with 1/7 twist.. should have been the default. As for the trigger... no excuse. Still... a real decent first show.
 

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I ran an EOTech in a Larue mount on my XCR, no problems at all. No marks on the rails, no problem keeping a zero; it fit perfect. The only thing I've heard of that doesn't work is the KAC VFG.
My concern is the design of the Larue mounting system... clearly Mark intended full rails with his design...
 

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The lightening cuts being down the center, I don't see how they are going to interfere with the correct fit of a larue mount. The contact points of mount-to-rail are shaped exactly the same unless there are some other cuts I'm not aware of?
Flip your Larue mount over and take a look... the problem is not interference... its the lack of it. Larue designs their mounts to hold fast at the center of the rail cut... the exact area the lightning cuts have milled away...
 

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I have Larue mounts on my XCR and there's not a problem. Ipso facto, lightning cuts aren't an issue. More intarwebz bullshit laid to rest.
Flip your Laure mount over... do you see the locking tits? They are there to prevent forward and rearward movement of the mount during hard use. These locking tits are in the CENTER of the Larue mount... yep... right where the rail is milled away. If you have a Laure mount... flip it over... it is obvious... just look. Of course... your safe queens will not encounter any problems, but hard use...
 

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Are they not wide enough to contact the XCR rail?
They do not go fully across the mount (like ARMS)... the tits are only in the center... they are designed to grab the rail exactly where the lightning cut has removed the rail... thus my reason I would like to see a full rail without the lightning cuts... especially the rail section over the receiver. When I get my camera back... I will post a picture... the concern is obvious once you look at the size of the tits.. and where they are positioned on the Laure mount.
 

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Thanks for the picture... as one can see... Larue placed the locking tits in the center... designed to grab the center of the rail lugs and prevent forward and backward movement. With a lightning cut rail... the center is now milled away. Is there enough meat on the side of the tits to engage a lightning cut rail? At the very best... there may be just enough for the corners to barely engage the angle cut of the rail... certainly nowhere near optimal... and certainly not as the original design intended... thats for sure! I will guarantee you this much... Mark Larue designed his mount for a full cut rail, ask him. Is the minimal engagement of the locking tits good enough for a safe queen or very light use range toy, probably... but "good enough" does not cut it for folks with hard use firearms. I for one would certainly prefer a full rail with my Larue mount, especially the top rail... where the optics mount... YMMV.
 

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I shouldn't feed the troll, but what the hell. I've got a free hour.

Again, if you actually look at the Larue mount and the XCRs rail, you will see it engages the rail quite adequately. The lugs engage about halfway into the heaviest part of the rail. That's enough to do what it's supposed to do. Most of the heavy lifting from the mount's viewpoint is done by the cam. This is a .223 rifle. It doesn't require a whole helluva lot to locate the mount. If it were on a .50, I might be concerned. Not on a .223 or something similar.

As for hard use...hah. The only thing getting hard use here is slag's mouth--or fingers in this case. This whole thing is a non-issue born in the fevered imaginations over in the cesspool of arfkom. Personally, I'd rather this sort of thing stayed over there. I get enough idiocy at work and there's more than enough on the internet. We certainly need no more here.
Here is a tip for ya skippy... when folks use the term hard use.. they aren't talking bench resting a rifle... and the hard use it gets from that strenuous 5.56 recoil :D ...

Don't think a Larue mount and a lightning cut rail is a problem? Fine.. but don't go asking Mark Larue's opinion... unless you want the straight poop that is...
 

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Regardless of your no doubt thorough "Internet Testing" slag (couldn't resist that one), no one has reported any problems with Larue on the XCR. In fact, its the complete opposite, NO ONE has reported a problem.
It's "internet testing" when one doesn't own an example... or even held one in their hands... in this case I have an example of each... so once again... I'm not qualified to internet test this setup... ;)

IMO Larue is top shelf... and I would like to run their mounts with my XCR... but such is not going to be the case.

BTW... this is a perfect example when the products in question will function perfectly together... during internet testing.. but not be ideally suited for each other in the real world... ;D
 

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Regardless of your no doubt thorough "Internet Testing" slag (couldn't resist that one), no one has reported any problems with Larue on the XCR. In fact, its the complete opposite, NO ONE has reported a problem.
It's "internet testing" when one doesn't own an example... or even held one in their hands... in this case I have an example of each... so once again... I'm not qualified to internet test this setup... ;)

IMO Larue is top shelf... and I would like to run their mounts with my XCR... but such is not going to be the case.

BTW... this is a perfect example when the products in question will function perfectly together... during internet testing.. but not be ideally suited for each other in the real world... ;D
Have you ever run any Larue mounts on your XCR?
Reading is fundamental... as posted right above your post:
IMO Larue is top shelf... and I would like to run their mounts with my XCR... but such is not going to be the case.

The Larue mounting system is designed for full cut rails... my XCR has lightning cuts. Given this design incompatibility... my personal experience/inspection of mounting my Larue Eotech riser on my XCR... and how I plan to put my XCR to use... I have elected not to run Larue mounts on my current XCR. For your's or other's intended purpose... such as bench shooting or safe queening... you may get by with this design incompatibility... YMMV.
 

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Yeah, we have a troll.

So now we get the pleasure of the "kool-kids" pontificating we see so much of on arfkom. Experience garnered from the likes of Counterstrike, Rainbow 6, etc., peddled on assorted forums because someone saw it on arfkom and repeats it ad nauseum on whatever site he runs across. Mostly just because he can.

My real world experience says otherwise. Which means a helluva a lot more to me than what some crotchpheasant comes up with from benchracing equipment on arfkom. Whatever. You all can make your own calls on this issue.
Glad to see the Larue mount is working out so splendidly on your queen... ;D
 

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This can be real simply solved by applying some chalk to either the "tits" on a Larue mount, or the edges of one of the rail sections... then putting the mount on there, pressing them together, and seeing how much contact you have after taking off the mount. If its even 1/16th on either side of the tit, I imagine that is more than enough to stop fore and aft movement even with the mount entirely unclamped. It isn't going to take much contact to keep it in place. Remember the thing is clamped down.

If there is no contact with the tit, get a mount with a full cross bar. BFD.
Nothing really here to solve... 85%-95% of the locking tit will not make contact with the rail face. This may be good enough for some... but not others... depends on your use. The choice is yours...
 

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So you think your .223 is going to recoil enough to shear off 10% of the metal of the tit on the bottom side of the larue mount?

I'll test it when my rifle comes in, and there won't be any more 85-95 percent estimating going on.
You yankees just don't read very well do you? :D Go back about 8 posts... where I said this:

Here is a tip for ya skippy... when folks use the term hard use.. they aren't talking bench resting a rifle... and the hard use it gets from that strenuous 5.56 recoil ;D

Tell you what... ask the man himself what he thinks about his mount system and it's use on lightning cut rails ---> Mark Laure... he will give ya the straight poop on it...
 

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Thanks... very constructive.

I guess that clears up why you've apparently been branded a troll.
It clears up 3 things... you don't read posts before you respond... you don't listen to answers... and you don't seek Mark Laure's advice...

I have a hunch that your "hard use" of the XCR will not encounter any trouble at all with this combination... ;)
 

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Once again chief... reading is fundamental... I'm not running Larue mounts on my XCR... and have no plans to run Larue mounts on my XCR... why? Because Larue mounts are designed for full rails... and my XCR has lightning cut rails...

Larue is top shelf? Well no shit Sherlock... that is because Mark designs a good product... key word here Sherlock... designs... as in his mount is designed for a full rail.. not one that is lightning cut...

Tell ya what chief... you sound like a real important fella... get the poop from the source... hell.. and important operator like yourself probably has his cell number on speed dial... just ask Mark next time your chattin with him ;)
 

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Can someone explain the differance between the full rails & the lightning cut rails? Pictures would help.
Full lug rail:


Lightning cut rail (notice center of each rail lug is milled out):


Larue mount... notice tits in the center of the mount.. to prevent fore/aft movement/shifting..



Larue makes rails and mounts... guess what rail style he offers? Yeah... full... imagine that... :duh:
 

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My eotech 553 uses arms rails but has the "tit" & Im no know all, but wouldnt the optic or what ever the mounts holding probly be pretty screwed up before they moved I took & bashed mine with the palm of my hand several times and grabed it and pulled it every which way as hard as I could with no shift, I know thats not hard use like being thrown out a 2 story building several times or what ever, & Im not trying to join in the argument & I dont want into eotechs vs aimpoints durability either... just asking. Is the hard use that your refering to the kinda trashing where drop the rifle out of a building onto concrete and things of that nature that its the only thing I can think of that might have enough force & shock to knock a mount around???
The ARMS mount has the locking tits located on the opposing sides of the mount, not the center... they are exactly inverse of the Larue mount design. ARMS are designed to grab a lightning cut rail, right where the meat remains for each cut rail lug. Also... this is not just about optics... although they potentially have the greatest impact caused by shifting. Think about a VFG, flashlights... or any other rail attached devices.
 

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Ranley,

I think you know what "hard use" really is. When you drop your rifle in cow crap and use your hand to wipe it off, that's pretty hard use to me :banghead:
I would classify that as "smelly use"... unless Ranley really wiped the rifle off with his bare hands... that would be hard core! ;D
 

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OK chief... so now you agree Laure is designed for full cut rails...

Now read my posts... carefully.... I collected them up for your convenience.. notice I state again and again... my reasoning for choosing not to run the Larue on a lightning cut rail... which is due to their design incompatibility with such. I also tell others "YMMV", "the choice is yours", "no where near optimal", "not as the original design intended", "good enough for some".... one thing I never said is it flat won't work... in fact... I state for some intended usages it may not even be a problem at all. The Laure mount is working out great for you? Boy... that sure is swell! As for me... I have no plans on running this configuration... and I have stated my reasons why... again... YMMV.

Bears repeating (for the slow and dim): It "may be good enough for some"... your comfortable with just the corners of the Larue tits minimally engaging the lightning cut rail lug... I'm not... :2cents:

Back to the rez... "chief"... reading is fundamental... don't read so well? Look at the pictures... dummy...


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With a lightning cut rail... the center is now milled away. Is there enough meat on the side of the tits to engage a lightning cut rail? At the very best... there may be just enough for the corners to barely engage the angle cut of the rail... certainly nowhere near optimal... and certainly not as the original design intended... thats for sure!

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Nothing really here to solve... 85%-95% of the locking tit will not make contact with the rail face. This may be good enough for some... but not others... depends on your use. The choice is yours...

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The Larue mounting system is designed for full cut rails... my XCR has lightning cuts. Given this design incompatibility... my personal experience/inspection of mounting my Larue Eotech riser on my XCR... and how I plan to put my XCR to use... I have elected not to run Larue mounts on my current XCR. For your's or other's intended purpose... such as bench shooting or safe queening... you may get by with this design incompatibility... YMMV.

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Nothing really here to solve... 85%-95% of the locking tit will not make contact with the rail face. This may be good enough for some... but not others... depends on your use. The choice is yours...
 

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My .02-
I would not have bought the XCR if it didn't have the lightening cuts. The rifle is already just a tiny bit front heavy and that would put it over the top for me. I think they Robarm should work really really hard at dropping more weight out of it, not adding more.
Any weight reduction is most welcome... I would take full rail lug in the optics area though...
 
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