Out of spec Larue Rail?

AR/M4 AR Technical Discussion
1

I set out last night to install my dads Larue LT 7.0 on his upper. I got everything off, put the rail on, put the rifle back together. when we went to mount his eotech however, it wouldnt mount (mounted to upper reciever bridged with rail). Mind you the rail is on straight. However, the bottom left side of the eotech was making contact with the float tube nut, thus, not allowing the sight to be mounted properly, however, the rail is centered with the receiver.

Apparently what happened is the left side of the rail (looking from butt stock) has just a little more metal on it, or it sits too low, causing the eotech to be sort of canted into the nut. Its hard to tell which one it is.

Looking at it though, with the sight on there, its obvious that the rail causes one side of the sight to sit higher then the other.

I just installed a larue 7.0 rail on my rifle and couldnt be happier, i love the thing. Ive never herd of Larue making an out of spec product. Were gonna talk to them today and see what we can work out, im sure larue will make things right.

Have any of yall ever herd of anything like this happening? my dad must have gotten the 1 in 10,000,000 that slipped by.

-Ryan

2

I’ve never heard of that either … but it can happen to anyone’s product. I’m sure they will make it right if there is a an issue with the rail.

3

I thought the knurled rings on the LT rails were just too big in diameter to be bridging them? Are you sure it’s actually a spec thing and not just a clearance issue?

4

Solution: Don’t bridge the optic. Either put it on the receiver or the rail.

5

Yep, I can’t use a carry handle to align a Larue handguard because the ring interferes. Probably the same thing happening with your Eotech.

6

What model Eotech?

Also, I can’t extend an eotech 552/512 very far past the receiver on any of my Larue rail equipped guns due to the barrel nut. My eotechs made contact on the left side as well.

I think it is the way the Eotech mounts and not a problem with the Larue Rail.

7

im thinkin its the sight as well, i was just really puzzled because my 512 bridges my rail, barely but it bridges it. i have mine mounted with the sight locked on the last notch in the receiver.

we put the rail back on and the rail lines up properly, and the sight mounts, we just cant mount it real far forward.

8

Sounds like a clearance issue with the barrel nut.

9

i feel like a dumbass, i guess we werent tightening down the eotech enough. i was tightening the thumb screw to hand tight and the sight would pop off. after we tightened it with a screw driver, it seemed solid, i couldnt pop it off with my hand.

Edit: its defenately a tight fit, the left side of the eotech actually rests on the barrel nut, either that or its real close. i think that the barrel nut def causes some interference in mounting the sight though.

10

i also went ahead and moved my site back a little bit on the receiver, just to be safe.

larue is a great company, and ill be doing lots of business with them in the future. i dont wanna come across as slandering a great product… just wasnt aware that what i experienced is common.

11

[i]Doctor, it hurts when I do this.

So…Stop doing it.[/i]

Stop bridging your optic.

12

I wouldnt really want my Eotech directly touching my barrel nut anyway. They’re not exactly the most heat resistant items out there.

13

wouldnt bridging the optic to the reciever and rail with it touching the barrel nut, thus applying pressure defeat the purpose of a FF rail??

14

No.

Bridging an optic could effect the zero, as the slightest movement of the rail from the receiver will make the POI off.

The purpose of a FF rail is to not attach to the barrel. bridging the upper receiver to the rail with an optic, or carry handle, ect will still not touch the barrel. The FF rail is attached to the barrel nut only, so it would not per-say defeat the purpose of a FF rail, but would be a possibility of throwing off the zero of the optic. If an optic needs to be placed more out there, then thats what the canty mounts are for.

Also consider the KAC RasII, the Vltor system, the ARMS SIR, and others mount to the upper and extend to the rail.

15

You may not have the barrel nut in 100% alignment for the gas tube. If it’s off even 1-2% you’ll see it when mounting the rail to the spanner ring. With LaRue rails the rail centers itself with the locking ring and barrel nut. If the barrel nut is off, the rail will be off as well.

This is why I prefer the DD Lite Rails and RIS II rails. No barrel nut/gas tube alignment is required. I do use an rail alignment tool to keep the tops of the receiver and rail in alignment. The tool allows you to keep both at the same height. You can get it even without the tool or using a carry handle but it doesn’t work nearly as good or as quick.

16

thanks for all the responses guys.

since i like my eotech mounted a little farther forward, i decided to order an American Defense riser mount for it.

My dad decided hes gonna just keep his eotech farther back away from the barrel nut.

as for one of the earlier responses about mounting the eotech on the rail, i thought about this however, im concerned about not being able to maintain zero.

17

run this:

then you can mount it more forward AND get a lower co-witness

18

already ordered the american defense mount, it appears to be the exact same thing, only with more slots for more mounting options.