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Posted: 3/4/2008 2:10:15 PM EDT
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Alright, I'm at my wit's end. Maybe someone here has seen something like this. I've got a Bushy upper and I've put a 12" YHM free-float forearm on it. The forearm is crooked, however, so with attached iron the gun shoots way off. I thought at first it was the tube itself. I put a second one on and it lines up identical to the first. That's not the problem. I emailed YHM, and they say "sometimes the hole in the reciever that the barrel installs in is not perfectly straight. A fraction of an inch off at the barrel nut is multiplied over 12" of length. If this is the case, you can either live with it or replace the reciever." I ran that by my gunsmith, who dismissed it as poppycock. He thinks it's either a bad lot of YHM tubes or the barrel nut not threading onto the receiver properly. I asked him to test the barrel, which he did by dropping a rod down it, so we know it's not bent, but how does that determine whether or not it's straight on the receiver? And how can I tell if the threads for the barrel nut are straight without throwing cash at a replacement nut? I'm too heavily invested into this gun to not fix this, but I can't go tossing money at every little thing that *might* be wrong. Can anyone speak to this problem? I'm running out of hair dealing with this. This is not what I envisioned for my first AR. Having a hard time justifying another one already... Thanks for all the help. |
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Toward the end of the rifle, where the barrel should exit the free-float tube dead-center, it's instead located nearer to one side of the tube than the other. At first glance it looks like the barrel is bent. I had a gunsmith put the whole thing together. Looking at the threads on the receiver I can't imagine how it could possibly be cross-threaded and fit as flush to the receiver as it does. The threads show no damage either. I suppose it comes down to one of four things: 1. The barrel slot in the receiver is not straight, as suggested by YHM. I assume that would mean that the barrel itself is crooked after all. 2. The threads that secure the free-float tube to the barrel nut are off. I've tried two different tubes with exactly the same results, so this is possible. I've got a new nut incoming, so this and the next possibility will be ruled in/out shortly. 3. The threads which attach the nut to the receiver are off. 4. The threads on the receiver are off. So the nut or the receiver. What's funny is that I've pieced this rifle together over the last month, waiting on this part and that, making little mistakes in ordering and correcting them. This is the fourth or fifth time I've gotten out of bed thinking "this is the day my AR comes together!" It's been a tough month. One more week. Or two...then I can go live on the ranch a while. |
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Upper barrel socket that the barrel slips into could be off center line when milled, the barrel/float tube nut could be off, or you could have bent the upper barrel sockets/threads if the barrel nut/tube was over tightened (over torqued). Start with confirming that the muzzle is on the same centerline as the upper receiver (small line or dental floss should cover this down the top of the receiver to the end of the barrel). If the barrel/socket is straight with the centerline, then start checking the upper threads/barrel nut to confirm as they are being tightened. If off, the tube threads are not square, the end of the tube is going to oblong around the barrel as it's being spun on. If the upper socket threads are off/bent, then the tube will stay predominately to one side as it's being spun. P.S. Since this is a Bushmaster upper, are you sure that you didn't bend the upper barrel socket when you pull the barrel nut the first time? |
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My gunsmith did comment that the original barrel nut was completely oversaturated with LocTite. It did take some work to get off, as he tells it. Thank you for the tips. I'll try to dig up proper tools to measure these kinds of thing tomorrow. It's off by less than a half inch a 12" so I'm not geared up to work that precisely. Most likely I'll run the ideas by my gunsmith and see what we can dig up. |
I think you just found your answer if the upper barrel socket is bent. The use of either heating up the barrel nut or freezing it should have been used to remove the nut, and not the use of a cheater bar/pounding on the barrel nut wrench to get the nut to release. The next clue of something wrong would be that the upper left his shop without him noticing the barrel was not centered in the float tube. It's your money/choose of smiths that work on your units, but I think that when it's all said and done (read sounds like you will have to buy a replacement upper receiver on your own dime since he is not going to take the blame if the upper receiver barrel socket was bent), I would find another smith to work on AR rifles. |
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Since the barrel extension for the most part conforms to the upper barrel socket, facing the lip of the socket would help a little, but not if the socket/pocket is way bent. Also keep in mind that a new stripped upper receiver goes for around $80 and depending on what shop is doing the machining, you could hit this price pretty quick. Also to point out, you would remove the anodizing coating (the hard skin of the part with a RC of around 69 or better) and would be left with raw soft aluminum seating surface (read RC under 20, hence soft as butter). |
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I talked to my gunsmith today, who is a pretty skilled guy. He used heat to get the barrel nut off, and I'm inclined to believe that anything that went into his shop came out in no worse functional shape than it went in. We both missed the angled forearm at first though. I've actually been thinking about the replacement upper option. If the new barrel nut doesn't solve the problem I'm more inclined to just eat an extra $100 to be done with it than to ship the whole upper back to get checked out. I'm sure the shop I bought it from would look at it, but I'm in no mood to get in the middle of a pissing match between them, Yankee Hills, and my gunsmith about what's wrong and who did it. You guys have all been awesome, these forums are a treasure trove of great information. |
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