Something weird I noticed with Larue mounts

[d90king]

FWIW my Larue T-1 mounts do the same thing. They are adjusted VERY tight.

Has the mount been mounted tight for an extended period of time? I am wondering if it has dug a channel into the rail and that is where the movement is coming from? I have 3 T1's in 660's and have not experienced any movement that I could see at first glance, but I have also never looked that hard because they have never lost zero... Interested to see where this goes... Has anybody called LT and discussed this with them?

[vicious_cb]

Has the mount been mounted tight for an extended period of time? I am wondering if it has dug a channel into the rail and that is where the movement is coming from? I have 3 T1's in 660's and have not experienced any movement that I could see at first glance, but I have also never looked that hard because they have never lost zero... Interested to see where this goes... Has anybody called LT and discussed this with them?

Again the movement is very very small. Ive been using larue mounts for years and only noticed a few weeks ago. I wont conact larue unless I know this isnt just user error or something.

Anyway I would like to ask the help of the M4C community and see if they can replicate the movement Im experiencing. The procedure goes as follows:

-Attach your Larue mount in such a way that the recoil lug is pushed as far forward as possible and the lock the mount down. Be sure to keep forward pressure on the mount as you are locking it down.

-Now note the ledge thats created where the rear of the mount meets the rail as shown in my first pic. Its easily detectable from by just running a finger nail down the rear of the mount until you feel it hang up on the ledge.

-Then lock back and release your bolt 3-5 times, your rifle should be in the horizontal like how you would be firing it, each time checking if the ledge is still there.

Post back with your results, thanks.

Also for those of you that already replied, have you actually checked if the slight movement occurs? I ask because the movement is so small you cant really notice it even with witness marks like marker on the rail and the mount for example.

[Luke_Y]

I don't get it. Several people have replied that they don't have the issue. A couple people replied that they have observed it. You are concerned enough with it to post up detailed pics, give instructions, and ask everyone to try and replicate it.

But, you wont e-mail or call Larue to see if they consider it normal and acceptable?

Not busting your balls or anything, just not getting it. For the record I don't have the issue on any of mine and even took two mounts off, remounted, and sent the bolt home a few times for ya.

[Thomas M-4]

At what angle do you start feeling resistance? I know the instruction card say 45 degrees but mine starts at around 60+ degrees. Mine had a slight back to back movement and I just kept tightening it 1/8 turn at a time until it all went away. I do have a very small spot on the bottom of the rail were the anodizing has rubbed off but you wouldn't notice it unless you knew were to look. LMT upper BTW.

[d90king]

First off I did this only because you asked, if I am being honest about it I don't see how this really even matters at the end of the day based on the tolerances you describe. If it moves due to the natural inertia of your BCG moving and it doesn't effect anything, I really don't get why you care, or why you have exerted this much brain power thinking about it. If a quality optic is not holding zero because of it, that is a different story.

I am as finicky as anybody about my rifles, or firearms in general.

Rifles tested: All rifles have the mount mounted one slot behind the end of the receiver except for the 106. Even though the MRP is a Mono its placement is the same.

1 LMT MRP T1 in a LT660 mount sits flush to the rail and has zero movement when closing the bolt 6 times.

2 LMT MRP T1 LT660 same exact placement above with a 3X on a LT pivot. The mount is flush and identical to the rifle above. Same results after 6 times. I also checked the LT 649 3X mount and it had zero movement.

3 LWRCI M6A3 T1 LT 660 same placement as rifles above and same results after 6 times.

4 LT Stealth 18/13.2" Mark IV CQT in a LT106 it had the same results as the above rifles and had zero movement after dropping the bolt.

That is 5 mounts, on 4 rifles that are not demonstrating the "insert your definition" that you describe.

[vicious_cb]

First off I did this only because you asked, if I am being honest about it I don't see how this really even matters at the end of the day based on the tolerances you describe. If it moves due to the natural inertia of your BCG moving and it doesn't effect anything, I really don't get why you care, or why you have exerted this much brain power thinking about it. If a quality optic is not holding zero because of it, that is a different story.

I am as finicky as anybody about my rifles, or firearms in general.

Rifles tested: All rifles have the mount mounted one slot behind the end of the receiver except for the 106. Even though the MRP is a Mono its placement is the same.

1 LMT MRP T1 in a LT660 mount sits flush to the rail and has zero movement when closing the bolt 6 times.

2 LMT MRP T1 LT660 same exact placement above with a 3X on a LT pivot. The mount is flush and identical to the rifle above. Same results after 6 times. I also checked the LT 649 3X mount and it had zero movement.

3 LWRCI M6A3 T1 LT 660 same placement as rifles above and same results after 6 times.

4 LT Stealth 18/13.2" Mark IV CQT in a LT106 it had the same results as the above rifles and had zero movement after dropping the bolt.

That is 5 mounts, on 4 rifles that are not demonstrating the "insert your definition" that you describe.

Thanks for doing this. I guess it really doesnt matter since its not shifting zero or anything.

I noticed you said it sits flush to the rail. When the mount sits flush to the rail that means the mount did slide back a bit since you are supposed to start with the mount pushed forward. When the mount sits flush to the rail, ie there is no ledge that means the recoil lug has moved rearward against the back rail instead being pushed against the front rail. Once its sitting flush it will not move back anymore since the recoil lug is right against that rail. Unless you started with the mount already flush to the rear rail, your mount did move rearward. If it looks like the pic below your mount moved backwards in the rail gap.

[Thomas M-4]

Thanks for doing this. I guess it really doesnt matter since its not shifting zero or anything.

I noticed you said it sits flush to the rail. When the mount sits flush to the rail that means the mount did slide back a bit since you are supposed to start with the mount pushed forward. When the mount sits flush to the rail, ie there is no ledge that means the recoil lug has moved rearward against the back rail instead being pushed against the front rail. Once its sitting flush it will not move back anymore since the recoil lug is right against that rail. Unless you started with the mount already flush to the rear rail, your mount did move rearward. If it looks like the pic below your mount moved backwards in the rail gap.

At what angle do you start getting resistance on the arm?

[vicious_cb]

At what angle do you start getting resistance on the arm?

A little over 45. Maybe 50 or 55 degrees

[Thomas M-4]

A little over 45. Maybe 50 or 55 degrees

Mine is at least 60 degrees probably more if you read the adjustment card it states that results may very. At 45 -50 degrees mine will have back and forth movement like you describe just a slight amount. I just kept adjusting the nut 1/8 turn at a time and testing it. The larue mount is supposed to work on even out of spec rails.
Just have a a glass of wine and keep bumping it an 1/8 turn at a time till at least you are at the 60 or 70 range I am fairly certain you can adjust it out just go slow and keep bumping it at 1/8 turn. Mine went all at once meaning one adjustment it had the same amount of play then the next it was gone. I can hold the rifle by the mount and shake it hard and zero movement.

[vicious_cb]

The thing is, it ONLY moves when I send the bolt home. The thing locked down pretty good. I can grab the optic + mount and try to muscle it back but it wont budge. Then I release the bolt a few times and it starts to edge back.