AR Sponsor
Posted: 4/6/2009 10:13:20 AM EDT
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So I noticed my rail and barrel nut were rotating, this putting my sights out of alignment. Bought an ar tool, took everything off, retorqued barrel nut,put yhm ff rail back on, tightened it down, and it's still rotating with not too too much force. I get the sense that when I tighten the jam nut I end up loosening the barrel nut. Anyone had any luck with these rails? I feel like I've tried everything but the rail still rotates even with the anti rotation screws in. Would like to get to shoot before I move next month and lose cheap 100 and 300 yard range access
Thanks |
| The places on the barrel nut where the anti-rotation screws go in seems to be bulges out a bit, but I figure thats cause the screws are slightly larger than the holes they go into. And yes I'm using a flat head, after spending 25 on an armorers wrench and 40 on an action block it would be awesome not I have to buy the yhm too too, but if that's what it takes... :( |
| If your barrel nut is torqued properly, and the anti-rotate screws and lock nut are tight, you won't have any problems. You might need the yhm wrench to get the lock nut tightened sufficiently. A little lock-tite (blue,not red, and NOT on the barrel nut threads)won't hurt any either. |
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ok so here are pics of how much it will move normally (it will rotate the whole barrel nut assembly until the gas tube stops it), and the second is the barrel nut, with the area where the screws go in being slightly "enlarged" by the screws, is this normal? is it possible its been stretched and so the scews dont hold it tight anymore?
note: i did not initially install this rail, the previous owner of this gun did. I just noticed it was moving like .5cm right and left. http://farm4.static.flickr.com/3617/3419508894_0268066808.jpg?v=0 http://farm4.static.flickr.com/3580/3419508940_ef5298ff4d.jpg?v=0 |
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Your barrel nut absolutely shouldn't be rotating. What torque are you tightening it to? I'm having trouble imagining how you're applying enough force on the lock ring (without the proper tool) to loosen the barrel nut.
EDIT: It looks like the slots for the locking bolts on the barrel nut are belled at the rear, which is consistent with your picture of the rail installed (i.e., I think you may have screwed the rail too far back before tightening the locking ring.) Can you even pivot the upper forward on the lower with the rail that far back on the barrel nut? |
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not sure what you mean by pivot the upper on the lower. but when its all together, the rail rotates (as far as the gas tube will allow) from the recievers. ive been torquing to 30ftlbs then till the gas tube aligns, which is pretty much right there. should i try going to the next hole? i heard up to 80 is ok on the nut. for the rail locking ring ive got a flathead screwdriver and then some light taps w/ a hammer.
truth be told what ive learned so far is when i get a second AR, if the rail isnt installed at the factory, its DD omega or larue all the way |
| It looks like you've got the locking ring too close to the receiver, as fizassist pointed out. If you can lock the lower down in a vice (I have a lower vice block) use your carry handle to align and lock the FF rail with the flatop receiver. I didn't use the YH lock ring tool, rather, I had a small delrin block, which I used along with a hammer to tighten the lock ring down. I did use some blue locktight, and it hasn't moved a bit (and it's an older FF tube without the anti-rotation screw.) |
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Quoted:
not sure what you mean by pivot the upper on the lower. Two captive pins hold the upper to the lower. If you remove the rear one, does the upper freely pivot forward on the front one relative to the lower? Like this: 
See how much gap is between the locking ring and the upper receiver? but when its all together, the rail rotates (as far as the gas tube will allow) from the recievers. ive been torquing to 30ftlbs then till the gas tube aligns, which is pretty much right there. should i try going to the next hole? i heard up to 80 is ok on the nut. for the rail locking ring ive got a flathead screwdriver and then some light taps w/ a hammer.
Something still doesn't make sense to me. A few light taps on a screwdriver shouldn't loosen a barrel nut that's on to greater than 30 ft-lb. Just to verify, are you doing the following? (1) Tighten barrel nut only (no forearm, no locking ring) to >30 ft-lbs, lining up the gas tube hole (2) Thread locking ring & forearm onto barrel nut, only moving the forearm back to the point where the locking ring allows you to pivot the upper forward on the front pivot pin of the lower. (see picture above) (3) Line up the forearm with the upper rail. (4) Install locking screws in the forearm. (5) Tighten the locking ring. truth be told what ive learned so far is when i get a second AR, if the rail isnt installed at the factory, its DD omega or larue all the way
Those are both fine rails, but you may have the same difficulties with them as well. I suspect there is something wrong with the procedure so far. |
there is a thread on here explaining step by step with pics what to do try following that and see if the problem still exists.... i just took off a YHM rail  and put a Larue one on. ... it just wasn't the quality that i need on my rifle
i also have a DPMS free float on my 24" that is very nice also 
Oh and what are you using to torque it with??? i run a machine shop the torque wrenches seem to be out every 9 months and have to be recalibrated and ones of lesser quality (then Snap-on) have been completely unreliable. Sears torque wrenches come out of spec especially if you are using one that is calibrated say from 25 to 250 ft lbs.. try to find one that is calibrated in inch pounds so it has the torque spec in the middle of the tools range |
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