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Posted: 6/18/2006 4:29:54 PM EDT
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I recently purchased a new Stag Arms Upper with an ARMS #40A2 rear BUIS. I noticed that to get in the red at 50 yards I had to crank the windage all the way to the right as it was shooting way to the left. Since then, I have taken off the FSB and installed a 10" Troy free float railing system with a Troy Flip Up front sight. Surprisingly, I still have the same problem with my windage cranked the whole way to the right in order to center. I have read countless posts by others and their problems mostly lie in a crooked FSB, but since I have taken mine off and still have the same problem, I am not sure what is causing it. I have also taken the barrel off and put it back on with a nice fit between the upper receiver notch and the barrel pin (barrel pin looks to be in excellent condition with no sheering or anything funny). Does anyone have any idea as what could be causing this windage problem and possible fixes without sending it back to the company? |
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When you install the barrel onto the upper receiver, there is a little wiggle room in the extension pin to the receiver that can translate into the barrel being installed a little off index (read front sight not indexed top center/where it needs to be as the friction of the barrel nut to barrel flange pulls the barrel extension pin to one side of the receiver channel). The two solutions are, Remove and reinstall the barrel while shimming the extension pin in the upper receiver slot socket; remembering to bore sight the centered sights to make sure that once the barrel is placed then tightened, the sights are looking at the same point as the bore. Or, To use a leather mallet and drift the entire tightened barrel in the upper socket via holding on to only the upper receiver, and making blows to the base of the FSB to slip/re-index the barrel to accomplish the re-indexing using live fire to determine the needed amount of slippage needed. Since you may be new to the sight and wondering which method I use, you want to borrow my leather mallet.  P.S. Welcome to the site. |
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Well after days of pounding the living snot out of the barrel with a rubber mallet, I have not noticed any change. When I went to the range, it was still shooting way to the left (6" left at 50 yards) with the rear sight windage maxed out all the way to the right. I've pounded the barrel with the barrel nut tightened, with the barrel nut loose, with the receiver in a vise, everything. I've also shimmed down the barrel extension pin some and opened up the receiver notch a few millimeters with a dremel which still doesnt seem to have any effect. Does anyone else still have any ideas as to how to get this barrel aligned or am I gonna eventually have to have a gunsmith align the barrel (and estimates on price? $$$) |
Well that is what I do as a last result ( In fact I just finished doing just that to my bud's 20" HBAR that was shooting 6" to the left at 50 yds. and Rear sights max'd out all the way to the right, I would say that if that you took off some meat from the pin or the slot on the receiver and you had no effect...there is something way bigger wrong. |
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well since i replaced the factory FSB with a low profile gas block, the FSB can't be the problem since I am not using it for aiming purposes. As far as I can tell the low profile gas block is lined up with the barrel pin which is also lined up with the flash hider. Also, when I mounted my EOtech on my receiver, the windage was dead on right out of the box so I don't think that the receiver rails are canted or out of geometry. Maybe I should trim down the left side of the receiver notch a little instead of the right side? For now, I'm tired of pissing with it, especially since for now I have the EOtech zeroed and shoots pretty good. Maybe when I get back from vacation I'll try messing with it again after I'm all rested up h If it is shooting to the left, do I want to shim down the left side of the barrel pin or receiver notch or was shimming down the right side the right way to go? |
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Hi... I just bought a stag 2H upper too, and I'm having similar problems. Took it to the range this weekend, and my shots were about 4-5 inches to the left at 25 yards. Had to adjust the ARMS#40A2 all the way to the right to get the shots centered. I haven't taken the barrel nut off yet... just ordered the tools this morning. Assuming the flat-top and the rear BUIS are true, and you're shooting to the left, then your front sight base is canted to the right. So... You would need to do whatever is needed to the notch and/or barrel index pin to rotate the barrel to the left (counter-clockwise). Assuming the front sight base is true, and you're shooting to the left, then maybe the rear sight is screwed-up and sits too far to the left. Are you still shooting to the left with your front sight mounted on your free float tube? (Not sure if you have it mounted on the tube or on your gas block.) If so, then I don't think rotating the barrel will have any effect, assuming the barrel and upper receiver are true. I'm thinking your problem (and mine problem) may be the ARMS#40A2... Mine looks a little cock-eyed, but it's hard to tell. jim
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Pulling my head out of my ass, The barrel is fine, its the float tube (with flip up front sight on the tube) that needs to be re-indexed to correct the sights. |
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Some more info about my issue... I'm pretty sure my problem is NOT a canted front sight base... It appears to be the ARMS#40A2 or the rail. I untightened the sight, and it's kinda wobbly - it doesn't sit nicely. When I tighten it back-up (with it flipped up), I can see the whole assembly tilt a few degrees to the left.... That's gotta be the problem. I mounted the ARMS on a RRA upper that I have, and it fits nice and snug and doesn't tilt when it is tightened. I also tried to sight-in the stag upper using a regular carry handle, and things were fine. No excessive windage adjustment was needed. So... My conclusion is that the ARMS#40A2 and the stag upper that it came with, don't play nice together. Bummer...
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"To use a leather mallet and drift the entire tightened barrel in the upper socket via holding on to only the upper receiver" This had to be done on a 16" carbine I put together. I got the upper from the guy at the show that builds them for you right there. It was shooting to one side and I took it back, explaining the problem. He took his mallet and hit the front sight exactly like Dano said, rotating the barrel in the receiver, and it shot straight. It's a nice upper; Kaiser receiver, bolt and carrier from Bushmaster and an Olympic 16" heavy, fluted, non-chrome 1:9 pre-ban barrel. The best thing about it is, the finish matches the Bushmaster lower perfectly, and the two receivers mate like they were fitted together - kind of unusual to get matches like that by accident. I don't use a wedge in it or anything else to tighten the fit. Anyway, the aperture in the A2 sight is right on the centerline after going back to the range, and he did that with only one whack with the mallet. I'd say that was a pretty educated whack. |
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