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[ARCHIVED THREAD] - Excessive windage (Page 1 of 2)
Posted: 12/21/2003 4:04:19 PM EDT
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Yes I read the FAQs and the barrel is installed with the FSB straight up and down now. It takes 24 clicks of windage to get it on and it holding good groups it just takes a LOT of windage to get it on target. My thoughts at this point are that the crown is the culprit. Going to get it crowned but in the mean time, Can anyone suggest anything else? IPSC_GUY sends |
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A bad crown will cause bad grouping, but won't put the shot off 12" if you have 1/2 MOA clicks. If the crown had a bur, then it may catch the bullet on the way out, but you would still be grouping sporadically on the target. If your getting 2" or better groups, then just drift the barrel in the upper receiver with a leather mallet to allow the rear sight to be centered and zeroed. Hold the upper receiver in one hand, and strike the front sight tower just above the barrel. This will slip the entire barrel in the upper socket, and not just the front sight tower on the barrel. And, even when I use a sight bar to align the front sight to the carry handle during a barrel install, I still have to fire for effect and drift the barrel to have the rear sight centered for zero. |
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You can align the sights/front tower anyway you want to during the barrel install, but until you fire for effect, you have no way of knowing exactly where the bullet is going to go. Also, when you tighten the barrel, you may get slight index drift. Unless you plan on fighting/re-installing the barrel a multitude of times, just index the front tower close to where you think it belongs, then drift the barrel in the upper socket to finalize the indexing/zeroing of the front sight tower once you see where the rifle is printing. Hell, just by changing the type of ammo you are using, you can change the POI by over 4 inches at 100 yards. So for me, I can mount a barrel in about 3 minutes using a sight bar tool, then put the rifle on the range for live fire, and by using a mallet to drift the barrel to adjust the sight tower index (without having to go back to the shop), have the rifle zeroed (with the rear sight dead center) in less than 10 shots for a total time of 5 minutes spent on completing a barrel install and zeroing. |
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Please explain. What is a front sight alignment bar. I seen it on the Armalite website where they sold them but it doesn't show one or explain. Also.. when you're whacking the front sight with the knetic impact device.. the barrel can only slip to a point where the alignment pin of the barrel bottoms out on the notch in the receiver. After that point am I to understand that you're physically BENDING the front sight???? |
| I'm pretty sure that the Al of the upper will displace before you bend the hardened alignment pin. Having done this a lot (just last night) I have never seen damage from it. The rifle I worked on last night had been previously assemled and zeroed (by whacking) then the barrel was removed and a MB permanently attached. No damage to the slot, or pin, was noted at that time. Both times after assembly the barrel shot to the right edge of the standard zero target at 25M. Two light hits to the FSB (on the right side of the FSB) drifted the POI to very nearly center. |
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Quoted: Please explain. What is a front sight alignment bar. I seen it on the Armalite website where they sold them but it doesn't show one or explain. The bar tool is a long straight bar that comes to a point at the end. The bar locks into the carry handle (hole in the carry handle) and you index the barrel/front sight to the point during install. Also works to check the barrel/front sight tower after you have tighen the barre nut to see if the barrel slipped. |
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No, unless your hitting the tower too hard on a cast unit. By using a leather mallet, it drifts the barrel without marring the surface of the metal. Your just drifting the barrel, not trying to knock the front sight tower off the barrel. The barrel extension is retained in the upper socket by aplied pressure only of the barrel nut (35 to 80lbs) against it (surface to surface tension only). Because of this, the impact on the front sight will slip the extension (entire barrel) in the upper socket. The barrel nut will still be torque’d at what ever it was set at before, and you will not be able to move the barrel by hand after you have slipped the barrel. Note: if you are able to slip the barrel by hand, either before or after you have drifted the barrel, then the barrel nut was not tightened past 35lbs, and you will need to tighten the barrel nut up to the correct torque. |
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Tweak, Troy posted in another thread that the indexing pin was designed to shear off so it won't hert the pin hole in the upper receiver, is this true? One more thing, when you drift the barrel does the barrel move in the Barrel extension or does the barrel extension move with the barrel? From what you guys said it sounds like the extension moves too, am I right? |
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I can't see how they could. The pins are very hard and there isn't enough room above them (they'd hit the barrel nut) for them to come up out of their recess and allow the barrel to rotate. The alignment slot isn't wide enough for the pin to fit in it lengthwise so the pin can't be "turned" out of its recess. Short of breaking the pin off (which I can't see) I don't see how that could be. I have seen Al displaced on uppers with too narrow alignment slots that required the barrels to be tapped in with a mallet. |
| Please, don't beat on it. You are either loosening the alignment notch by beating on it or the front sight base is rotating on the barrel. In my opinion, this is not the way to correct this problem. You can get a clamp on front sight base from Armalite. They look almost like the factory (no bayo lug)and they are CMP approved. |
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IPSC_GUY, It sounds to me by how far your windage is off, at 24 clicks, that it could be a bent indexing pin. I don't know if hiting it with a mallet will work, there are some people like me that aren't sold on drifting the barrel. If it were me I'd take the barrel off and see if that pin is bent, if it is take out the old bent pin and buy a new one (they only cost $1.50) then put the barrel back on. but if you don't have the tools send it back to Bushmaster I'm sure thay will fix it. |
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Quoted: Please, don't beat on it. You are either loosening the alignment notch by beating on it or the front sight base is rotating on the barrel. In my opinion, this is not the way to correct this problem. You can get a clamp on front sight base from Armalite. They look almost like the factory (no bayo lug)and they are CMP approved. Just FYI...the procedure posted by Dano523 and Tweak is in the Marine Corps manual. I'm not sure the military would be doing it if it was not a good idea. If you've ever removed a FSB, you'll know that it ain't gonna be turning on the barrel. A couple whacks to the FSB is alot cheaper than the Armalite base. Besides, when you mount the Armalite base on a improperly indexed barrel, you run the risk of not being correctly aligned with the gas port. |
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Well, the Marine Corps has never been known to be gentle on anything! I just don't like the idea of moving it with the mallet. I am offering an alternative method. I'm not going to try to correct a rifle in this manner. Gas port alignment issue: The gas hole in the sight base is much larger than the gas port in the barrel to allow for a small amount of misalignment. If the rear sight is all the way to one side, to get centered up for windage (some cannot be centered up even then),that means that the front sight needs to be moved the same amount in order to center up the rear. That's quite a bit of movement. The fit between the index pins and the slots in my uppers are not that generous. Yes, I have removed a FSB. I know about the taper pins. It is a very solid way to mount the front sight. I simply stated that either it was moving (doubtful) or the barrel extension was moving. Since it is the barrel extension that's rotating, then the index pin slot is either oversize or the pin is displacing metal in the index slot in the upper. Michael Carter |
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Quoted: that means that the front sight needs to be moved the same amount in order to center up the rear. Lots of math here so I'll cut and paste a previous discussion on this topic. From rex of the AR15-L The barrel extension has ~.5" radius and the FS height is ~2.5", so a .001" movement of the indexing pin will move the FS ~ .005" A 20" barrel has sight radius is ~19.75", and using similar triangles, a .005" FS movement will move the POI .005" x 100 yd * 3 ft/yd X 12"/ft)/19.75" = .91" A rough approximation that is easy to remember is that a .001" movement of the indexing pin will move POI 1 MOA with a 20" barrel. For other barrel lengths it scales as the inverse ratio of the sight radii, e.g., for a 16" the sight radius is ~14.75, so the POI moves 19.75/14.75 X .91" = 1.24" for each .001" movement of the indexing pin. An good approximation is that a .001" movement of the indexing pin will move the POI 1.25 MOA with a 16" barrel. [b]Bradd_D[/b], The USMC manual, TM 05538C-23&P/2 OCT84, that I have on hand does not show the "whack it" trick. It describes the same method outlined in the USA manuals, align while tightening. [b]IPSC-GUY[/b], Your sights are off 24 clicks at what range with which sight radius? |
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Quoted: [b]Bradd_D[/b], The USMC manual, TM 05538C-23&P/2 OCT84, that I have on hand does not show the "whack it" trick. It describes the same method outlined in the USA manuals, align while tightening. That's what I get for listening to people on the internet! [BD] |
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Tweak, No kidding, i am sure I saw that in my manual. It is the same as yours (84 with about 200 pages). I tend to read maintenance manuals cover to cover, and it was in a trouble shooting area, not the regular barrel mounting instructions. They did say to wack it, but not on the sight base. I couldn,t figure exactly how and where they wanted the hammer blows to fall (no pictures) and I didn't want to persue it as I wasn't keen on pounding on my new upper. Of course, I did buy it in Ga..... And I do use spit to lube round balls in my smoke pole. |
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I certainly don’t want to be disseminating erroneous information, so when I got home tonight I went through my USMC manual and I could not find any reference to hitting the sight post/base with a hammer. In fact, the only reference I found to “excessive windage” recommends replacing the upper receiver. ar-wrench and Bradd_D, I know I’ve read the “hammer technique” in some manual, but I can’t find it. You guys know where you saw it? |
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Bookhound, The method is demonstrated in Martin & Tillman's book, "The Complete Guide to AR-15 Accuracy." I've been told that it is also shown in the [s]BFI ass'y vider[/s][i] Bushmaster Firearms Inc video that details how to assemble the AR[/i] but do not have a copy to verify same. |
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My brother made off with my manual. I am pretty sure (after looking on the net) it is the same version of Tweak's marine manual, dated 1984. Sorry, if it was here, I would have posted a pic, or admitted my Georgia Goof. I did, however, find a clear reference to straightening bent barrels by hand, and them being OK for return to service. In the Army depot manual. "Whack it" and "Snatch it" are the same schools of thought. |
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I'm having the same problem. My brand new Bushmaster has a standard 16" barrel with carbine sight radius (not a dissy). The rear sight I'm using is an ARMS#40 set in the rear-most notch. At 60 feet I'm using 20 clicks of left windage to hit center. The front sight is canted to the left ever so slightly. In fact, I didn't even notice it until I measured it with a striaght edge. The ARMS sight appears to be squarely in the notch. This seems pretty extreme for 60 feet. Is this a candidate for the whapping method or is it better handled by sending it back to Bushmaster? I have very limited experience with gunsmithing and don't want to get in over my head. I'm told Bushmaster parkerizes the barrel assembly after the front sight tower is installed. If that's the case then would "drifting" the tower base cause the parkerizing to chip or flake off? Thanks |
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Quoted: At 60 feet I'm using 20 clicks of left windage to hit center. That's kinda extreme at 18m. I'd send that one back, it may be bent. If you rotate the barrel too far around you'll get into trouble with the timing of the bolt lugs and the alignment of the gas tube. You're allowed 12 clicks max using the A2 carbine when zeroed at 100m. If it's much more than 4" at 25, I don't like messing with it. I'm told Bushmaster parkerizes the barrel assembly after the front sight tower is installed. Yeah, funny how that gets around. If that's the case then would "drifting" the tower base cause the parkerizing to chip or flake off? Parkerizing does neiter though it can be rubbed off with enough effort. Either way, the front sight base does not rotate on the barrel. The barrel rotates in the upper. |
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Quoted: To whack it, or not to whack it, that is the question. There's a better way to correct a canted front sight than by beating on it with a big hammer. All you have to do is spin off the barrel nut and open up the upper receiver notch with a jeweler's file until the front sight is straight up. (Be careful and work slowly, because a tiny amount at the notch will make a noticeable difference in the front sight.) Probably the most important step is tightening up the loose side of the notch so the barrel won't rotate when you install the barrel nut. Do this by taking a small hammer and punch, and with the barrel in place very lightly peen down the threaded area next to the barrel pin. (Light taps!!! It doesn't take much!!) Now just reinstall the barrel - without over torquing it - and you're done! Quoted: Mine's heading back to BM with the ARMS#40 installed so they can zero it with the sight I'll be using. Now you know why I never buy assembled uppers - I don't want a rifle that was built by someone dumber than I am. [:D] [Edited to ficks speling misteaks.] |
[ARCHIVED THREAD] - Excessive windage (Page 1 of 2)
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