The distributor swapped an optic with a short rail and sold me the gun.

Rail keeps coming loose.

Distributor apologized and told to send the gun in but I'd like to fix on my own.

I'm gonna try loctite but I'm afraid it won't do it.

I've noticed a pin hole towards the front end of the rail.

Anybody know what it's for??? Maybe I could try punching in a roll pin to keep it from wiggling itself out??

Thanks

Blue LocTite is awesome. Make sure the bolts will hold it on their own, and the mating surfaces are clean. Then add the LocTite.

Wiped the thread and the mating surfaces with 91% alcohol,Dried for 15 min, applied loctite, applied quite a bit of torque.

Now we wait.

Any knowledge on the pin hole?

I might as well put a roll pin in.

Acetone is superior for degreasing. You can add a roll pin if it makes you feel better, but it won't hold anything by itself. 

The pin hole is there because they thought about putting one there but decided not to. It doesn't need it, loctite would do more for it than a pin.

Another vote for thread locker.

I've swapped multiple rails and haven't had any problems when using thread locker.

AJ

Last or second time it came loose, it was after roughly a hundred rounds.

The first time it came loose, it was after about 30 rounds.

Shot about 100 some rounds today and the rail seems to be holding ok.

I'm honestly surprised that the loctite fixed the problem, hopefully it did. I always saw it as a half ass solution to locking nuts in tight, kinda like duct taping.

I swapped out the short rail on my A3 for the long miltary rail a while ago - I haven't shot it much if you look at my other thread But with some blue loctite, it's been rock solid since I installed it, a few years and around 300 rounds ago...

There's not much acting on the rail, so once it's on and loctited down, it should be good to go.

It is only half the solution. Proper torque is the other half. 

Anybody remember the torque spec?  I already forgot it. 

OP:

as noted above, pull the rail and the fasteners clean all parts and threaded holes thoroughly with isopropanol and let dry.

Apply quality Loctite to the threads and torque to spec.  I always personally add a couple pounds.....literally, just a couple.

I've never seen a listed spec for that. I suspect in the neighborhood of 35 in-lb.
I mostly go by feel for torque specs. 

I know the torque spec and I think it's too high. It's the same spec for the scope turrets, which I also think is too high.

Loctite plus "good and tight" (not excessive) is adequate.

When is fastener is lubricated (like with liquid thread locker) you need less torque to get the same clamping force. Torque specs are commonly quoted for dry fasteners.

If you're using a T handle allen driver, tighten until the hex part of the driver starts to flex from the torque.

Chart showing common torque specs for lubricated and dry fasteners here: https://www.fastenal.com/content/feds/pdf/Torque-Tension%20Chart%20for%20Metric%20Fasteners.pdf

4mm lubricated should be 0.7ft/lbs.

AJ

Holy shit thank god.

I got worried when people started talking about torque spec because when I was torquing it, I did so in a manner of leaving the rail permanently on the receiver.

I took a hex key and a vise grip to get a firm grip on the shorter end. Tightened until the key started to flex then another good flex, or to the point where hex key aint gonna stay straight if I went past that point. I don't have a torque wrench and I don't know what it feels like to add a few pounds to the spec because this is largely subjective and one would need a lot of torquing to get a hang of it.


The deed's been done already and shooting will only tell me if I did it correctly. As I said, I've shot about 100 rounds and it seems to be holding ok.

And I'm not exactly sure what Maleante meant by too high.

And I didn't know "quality loctite" was a thing. If you were talking about genuine brands, I used blue 242, shoulda gone with red


On a side note, this is probably a total overkill but



The thing fit right in.

What I mean is that the value given by Steyr, in my opinion, is too high. Perhaps some won't agree with me going against the factory spec, but I think the torque value is excessive.

Using loctite (blue) or rocksett and getting the bolts tight, but not crazy tight, is well enough for any of the AUG rails/optics. If someone starts cranking down on a bolt, there's the chance that you strip out the threads of your rail or expensive optic housing.