SR-15 Out of Spec...?

[RandomUser404]

Hey guys,

I'll keep it short and sweet then delete this. I've just got a curiosity regarding my SR-15 Mod 1. I finally bought a Larue QD mount for my ACOG and when I went to install it I noticed that - fresh out of the box it fit my URX rails perfectly. No adjustments needed. But when I put it on the upper rails it was loose as a barn door. I had to crank and crank the nut in order to get it to fit. Which means that:

The URX 3.1 and upper are obviously not the same size. Is this intentional? Doesn't seem like a Knights product should be this out of spec.

Also as long as I'm here. What's everyone's thoughts on threadkocker? Couldn't decide if I should use some or not

[hk_shootr]

How do you know the URX isn’t out of spec?

You could always look up the rail specs and get to measuring.

Personally,this is a non issue. The mount is adjustable and I wouldn’t mount an optic on the URX anyway.
I don’t see an issue here.

[TXBK]

Hey guys,

I'll keep it short and sweet then delete this. I've just got a curiosity regarding my SR-15 Mod 1. I finally bought a Larue QD mount for my ACOG and when I went to install it I noticed that - fresh out of the box it fit my URX rails perfectly. No adjustments needed. But when I put it on the upper rails it was loose as a barn door. I had to crank and crank the nut in order to get it to fit. Which means that:

The URX 3.1 and upper are obviously not the same size. Is this intentional? Doesn't seem like a Knights product should be this out of spec.

Also as long as I'm here. What's everyone's thoughts on threadkocker? Couldn't decide if I should use some or not

I take it that you haven’t contacted any of the manufacturers involved, which is a rule, here?

[Jaysop]

I take it that you haven’t contacted any of the manufacturers involved, which is a rule, here?

I know the guy is new, maybe hes just trying to figure out if this is an issue or not before going out and shooting everyone emails.

What's the point of joining a gun forum if we cant ask each other about things we dont know about?

When people read these forums it's pretty overwhelming all the talk about spec and tolerance stacking and a million other things.

As for the OP. I have a Larue LT104 on my SR15. It fits snug on the upper. I just tried it further out onto the top rail of the URX4 and I can't close the levers.

A Bobro mount fits snugly on both receiver and rail.

I wouldn't worry about it unless you have something you mean to mount onto the rail that wont fit. I think the design of the Larue mounts are to micro adjust to the specific rail. I always paint a witness mark on that nut.

Threadlocker on what? The nut on the mount or the rings?

[hk_shootr]

Blur thread locker on the rings, none on the mount lever

[TXBK]

I know the guy is new, maybe hes just trying to figure out if this is an issue or not before going out and shooting everyone emails.

What's the point of joining a gun forum if we cant ask each other about things we dont know about?

When people read these forums it's pretty overwhelming all the talk about spec and tolerance stacking and a million other things.

As for the OP. I have a Larue LT104 on my SR15. It fits snug on the upper. I just tried it further out onto the top rail of the URX4 and I can't close the levers.

A Bobro mount fits snugly on both receiver and rail.

I wouldn't worry about it unless you have something you mean to mount onto the rail that wont fit. I think the design of the Larue mounts are to micro adjust to the specific rail. I always paint a witness mark on that nut.

Threadlocker on what? The nut on the mount or the rings?

I don’t know. I didn’t make the rules, but I did read them.

OP, it doesn’t matter. The optic mounts to the upper receiver and not the handguard. If that doesn’t cover your question, contact the manufacturers.

[RHINOWSO]

Why do you think all mounts have some manner of adjustment to get things to fit snug?

Because there are variances. I've moved scope mounts from weapon to weapon and they always need some adjustment to to snug them up right.

It's just the way it is.

[the_1iviper]

Hey guys,

I'll keep it short and sweet then delete this. I've just got a curiosity regarding my SR-15 Mod 1. I finally bought a Larue QD mount for my ACOG and when I went to install it I noticed that - fresh out of the box it fit my URX rails perfectly. No adjustments needed. But when I put it on the upper rails it was loose as a barn door. I had to crank and crank the nut in order to get it to fit. Which means that:

The URX 3.1 and upper are obviously not the same size. Is this intentional? Doesn't seem like a Knights product should be this out of spec.

Also as long as I'm here. What's everyone's thoughts on threadkocker? Couldn't decide if I should use some or not

clean and degrease the threads on the barrel nut and use blue threadlocker on the barrel nut , do not use threadlocker on the rail to upper receiver threads.

[MegademiC]

OP, if the mount adjusts enough to get tight and zero the gun, its good.
If not, contact KAC.

[RandomUser404]

@Jaysop

Thanks for the response man. I really appreciate it. Wasn't considering mounting it on the URX just thought that it was odd the 2 would be so different from such a high end manufacturer.

In terms of the threadlocker, I was considering putting it on the screws that hold the ACOG to the Larue Mount. Its the TA31 so no rings - just those 2 screws holding it to the mount. I noticed they were very easy to remove from my factory trijicon mount (like 1lbs of torque easy) and thought maybe I should put some on there. Yay or nay?

Lastly - how do you like the Bobro? I was debating between the LT100 and the Bobro but ultimately went with Larue because it seemed the less likely to fail due to the # of moving parts.

Thanks again for the help!