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Posted: 10/17/2008 11:52:38 PM EDT
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I have an issue I'm hoping someone can help me with. I put a Larue 7 inch FF on a brand new AR, since I installed the FF i have put maybe 500 rounds though it. When I first installed the FF I don't remember any rotating or looseness. But I also don't think I really tried to check. Just now I was messing with it and torquing the Vertical grip (not that hard though). It will rotate sightly now (a degree to each side?). But it only will rotate as much as the Keeper (Anti-Rotation Device) lets it. In other words- the Keeper straddles the upper receiver and the FF rotates so the keeper will bounce back and forth on each side of the receiver. And when I say the FF rotates I mean the whole thing; the entire assembly (Handguard Nut, Barrel Nut, and Handguard Rail). Is this normal? Should I take everything apart and reassemble? Pics of how it rotates Note how the Keeper seems to be the only thing from stopping it from rotating further. http://i426.photobucket.com/albums/pp343/jmanski/PA180133.jpg http://i426.photobucket.com/albums/pp343/jmanski/PA180132.jpg |
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I thought I put enough torque on it and I used correct tools, but there were issues getting the gas tube hole to line up correctly so I might have not have turned it far enough... I was thinking hard about how the free float actually attaches the the rife and it seems that the only part of the free float that it touching the rifle is the barrel nut. Even if I torqued the barrel nut down to 80 foot pounds I think I'd still be able to make the FF rotate like it does now. I don't like the play it has, and I'm worried about it slowly wearing on my gas tube. Should I just reinstall it and see what happens? I've been avoiding this because it's a pain. |
Is this the first LaRue rail you've ever installed? Just trying to gauge your experience. If the gastube hole isn't lined up properly, then the barrel nut isn't tight enough. I've sometimes came across situations where 1 hole is too loose and the next (seems to be) too tight. It's hard, but you have to line up the next whole on the barrel nut. I was taught you need 30-80 foot pounds of torque for the barrel nut. That being said, I've installed probably 20-30 LaRue rails and I've never used a torque wrench. I follow the instructions and tighten the barrel nut 3 times, and on the third time tighten up the barrel nut until the gastube holes in the barrel nut and upper line up damn near perfectly. I then tighten the handguard nut by hand until it won't budge. Then I use witness marks and a straps wrench to make sure its as tight as can be. Once everything's done right, the rail will NOT move side-to-side at all. |
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Aright good to know. I guess I got to tighten up the barrel nut more. When I was first installing the nut it did seem to come to one of those awkward spots where it was past one hole but didn't quite reach the other. I didn't want to break anything so I think I just backed it to the easy hole. This is my first true free float handguard by the way. |
I'm sorry for being ignorant but what do you mean by "witness marks"? |
I understand completely. A friend and I have both broken armorers wrenches before trying to line up the next hole, but we've never broken anything on the rail or upper reciever. It's hard, but it can be done if you go slowly and carefully. We use a DPMS Multi-tool when we are wrenching on guns, and if you use a breaker bar with the multitool, that might work to get that next hole lined up. It worked for us. I don't know if you're using any kind of grease or lube on the barrel nut and upper, but I use antisieze when I install LaRue rails and I like to think it helps a little. |
That's exactly what I meant. I put 2 pencil marks (1 on the rail that doesn't move and 1 on the handguard nut that does move) to gauge how much the handguard nut has moved when I've tightened it. I've probably installed 20-30 LaRue rails over the years. USMC03 (one of the moderators here) can vouch for me as we're always helping each other wrench on guns. If you need anymore help, feel free to ask me and I'll help out as much as I can. |
Now I have a question. I am having hell getting the flip up sights sighted in. I have a rail mounted Troy and a 40L rear. I run out of adjustment on the 40 and still shoots 4 or 5 inches to the left. I swear the Larue is not straight but it appears to be on right? |
One way I check to see if a rail is on straight or not is, before I start putting irons and optics back on, is I compare the upper reciever rail to the top rail of the LaRue. If it's not aligned properly, you'll be able to see a difference between the 2. Even if it's off by a hair, you'll see the difference. It can be a little time consuming because you'll have to keep sliding the rail on and off the upper, but in the long run, you'll be happy that it's on perfect. |
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If you don't have a receiver block, you WILL twist your upper when applying this much torque. Even with a block, often times you'll find that the BCG will hit some resistance near the ejection port due to minor deformation. Manually cycling the bolt several hundred times will clear this up. Some people put a bridging scope ring across the upper receiver to the top rail to set the timing. If you're using rail mounted iron sights, you'll have to be absolutely sure you time the handguard properly or you'll run out of windage trying to make up for the canting. Witness marks are your friends. A regular pencil will do you just fine. |
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