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Posted: 11/16/2006 7:41:44 PM EDT
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I read a post where someone stated that an overtight barrel will affect accuracy. Not long ago I installed an Armalite FF tube. The original barrel nut was VERY tight. We torqued the new barrel nut to 35 ft. lbs using a torque wrench on the multi tool. We then had to line up the slots on the barrel nut for the gas tube. We had to put a lot of force on the nut to tighten it enough to get the gas tube through. If we loosened it a little to try to line it up it was way too loose. In order to line it up we went far beyond 70 ft. pounds. After the FF tube was installed I shot it. The groups were not much tighter, if any. Could I have overtightened the barrel? How tight is too tight? How loose is too loose- under 35 ft. lbs.? Is using a torque wrench on the barrel wrench the accepted way to do it, or are our measurements skewed? Jim |
Yes, that's exactly how it should be done. As for why it isn't more accurate, what ammo are you using? How accurate was it before the install? Are you a good enough shot to notice a difference? |
I was using BH 68gr match and Win 45gr Varmint ammo. I had a scope on the rifle and sandbagged the rifle front and rear to check accuracy before and after. The after also had a new RRA NM trigger installed. i really expected the groups to shrink moticeably, but they are essentially the samo. The barrel being too tight was a concern before I went to the range but was unavoidable in order to line up the gap for the gas tube. I am thinking there is something I overlooked. Jim |
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What's the twist rate on your barrel? 1/9? You want to match your twist and bullet weights, although a 1/9 will shoot most loads decently. Another question, are you shooting with iron sights, or optics of some kind? My personal experience with FF tubes/hanguards has been that accuracy doesn't make a huge jump after installing. When I shoot from a bench, I'm not putting much, if any force on the handguards, so I don't see much of a difference. I've also had the "gotta torque the hell out of it to get the gas tube through" issue too, but never seen accuracy diminish from it yet. For me, changing triggers to a nice 2-stage, or even doing the 15-min trigger job (and mine always takes more than 15 minutes) has made a much bigger impact on my groups. |
You are right. www.ar15.com/forums/topic.html?b=3&f=4&t=142139
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That's what I read before starting. I think it may have exceeded 80# to line up the barrel nut. Jim |
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You probably could've saved yourself some money and tried some different ammo. I wish someone would tack this one statement: EVERY BARREL IS PREJUDICED AS TO WHAT LOADS IT LIKES. Yours might not like those two loads. First off, it might not like the bullet. This is usually the biggest factor, in my experience. But, it also might not like one loads powders over another. The combination of type of powder, type of bullet, and how fast they got it zinging are all factors. Also the OAL of the cartridge has some factor in it too. I have a really accurate AR, free floated, wylde chambered, ss wilson, actually it might be a woa barrel, I forget, but that thing shoots alot of loads well. But it absolutely despises the 69's. At least from the red box 69's from black hills. Now that bullet typically has a reputation, and that loading too, has a good rep for being real accurate. But my real accurate middy doesn't like it. Go figure. I have a colt that is finnicky about ammo. With Q3131A or ADCOM, it'll group like 5 moa and sometimes worse. I give it some 75's, 77's or 68's and it shoots pretty well. That other rifle I mentioned earlier will consistently put Q3131A under 2MOA. And the ADCOM under 3MOA, which I didn't expect it to do well. Neither one of those loads are meant to be stellar performers accuracy wise, yet my one rifle shoots them pretty decent consistently and the other hates them consistently. I could go on and on and many others on here could echo this too. Now, part of the problem is people don't take the time to do a scientific, or relatively scientific evaluation. People take it to the range, look at their targets and say, aww that's pretty good and guess how big the group is. And they don't exercise a consistent way to test. I'm going on and on, but either way, get yourself several different loads, shoot 5 or 10 shot groups at say 50 or 100 yards. If you got a scope 100 is good too, and make an evaluation of each load. Watch your barrel temp as it will shoot a little different the hotter it gets, and pick which one you like that you want to afford. Otherwise, just buy any ole stuff and shoot the crap out of your gun. That's fun too. I just like having a good idea on how my rifle performs with what load. Hope this helps. |
I wasn't complaining about the actual size of my groups. What I was curious about was why would the groups not improve after installing a FF tube and match trigger when shooting the same ammo. My rifle also likes different ammo- Adcom and WWB result in larger groups than the BH or Win varmint ammo, and that is expected. What is surprising is that my 1 in 9" barrel shoots the same size groups with the 68gr BH and the 45gr Win Varmint ammo. I just now thought about something else. My stock gas tube is under pressure from the FF tube. A new gas tube properly bent is on it's way, but the barrel right now isn't truly free floated. I'll check again after the new tube gets here. Jim |
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The Colt manual discusses troquing to 35 ft lbs. Then you will have to continue to tighten until the next hole or channel lines up properly for the gas tube. Everytime you have gone too far and need to back up you will have have to double check the torque. Accuracy problems are not always found in how a barrel is installed. There are several factors that come into play and can effect accuracy. Ammunition is a big factor as stated above. You may have to try several weights, styles, and manufactures to get the right load. This is usually the best place to start unless you want to upgrade the rifle. Mike |
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For the barrel torque spec, the breakdown is this: 30-35 pounds is what it takes to simply secure the barrel in the upper receiver, to eliminate play and make sure it stays tight. The remaining 50 pounds in the spec range is the allowance for getting the notch to align, that's all. You have a 50 pound wiggle space to account for odd barrel nuts or upper receiver threads. So, for accuracy concerns, you don't want or need that extra 50 pounds if you can get the notch to align at 30-35 pounds. Builders usually either use shims to get the nut to align close to the minimum torque or they try several different barrel nuts to see which one snugs up and aligns as they want it. Above 80 pounds, the danger is that the extension flange can crush the upper's threads like a crush washer and point the barrel slightly off axis or the barrel nut can grip the flange so tightly that further tightening with a barrel wrench can actually turn the the whole barrel, forcing the alignment pin to push into the side of the upper's slot. This will twist your front sight out of alignment. Remember, you're tightening hardened steel into aluminum. Aluminum loses. Try another barrel nut if you're close to 80 pounds. Barrel nuts are cheap and there's no reason to settle on one that aligns at 80 pounds like that. |
This barrel nut came with the FF tube and is needed for the tube to screw onto. Jim |
Try shimming it. But if the FF's nut requires that much torque, then I'd call the manufacturer and see about swapping for another one. Or try the nut on a different upper. |
Personally, I don't see how installing a free float tube will make your barrel shoot better. What'll do is keep your barrel from moving when you're putting pressure on the barrel. Like say if you have it bagged or you have it resting on a bipod. With a non free floated barrel, you just have to take care to not put alot of pressure on the barrel. Like a tight sling, etc. This may help your groups because your barrel is not going to move like it used to. But you haven't told us what kind of groups you were getting and I went into my rant because you only listed 2 types of ammo. You might already be reaching the limit of accuracy with your barrel. I don't know. There are several factors into accuracy and having it free floated is only one of them. And like I said, that doesn't necessarily make it more accurate. It may make it more consistent within different positions of shooting it. As far as what the other guy said about installing a barrel properly. I can't help you there. The advice sounds good, but I've never done it before. |
| I recommend shimming this one since you have installed it. Another method would be to tighten it up, loosen it, tighten it up again, loosen it, and keep repeating until it lines up at a reasonable torque. Also I am not surprized by your no-gain in accuracy. Shooting the float tube off of the bench and shooting your handguard off of the bench are probably pretty equal. If you were cranking on a sling in position the float tube would keep the point of impact from changing. |
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