Wandering zero or sights moving

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11 years 1 month ago #31469 by bollox
AR10B A4 rifle w/ the detachable carry handle and front sight.

Issue 1: Twice now the front sight has worked loose under fire. After the first time I lock-tited the thumbscrew and torqued wrench tight (used a flat file in the grooves of the thumbscrew). Worked loose again yesterday.

Issue 2: I was able to shift the carry handle fore and aft slightly after shooting yesterday.

Issue 3: Railed gas block APPEARS TO BE SLIDING FWD under fire on the gas port journal. While I haven't calipered the gap between the FF tube and the gas block it appears to be larger than it used to be and shiny metal is visible on the journal.

The aggregate of these issues means that every time I pick up my rifle I need to re zero. Elevation has shifted about 3 moa over the last 400 rds or so. Windage is more stable. Its shifted 1 moa.

Very interested to hear how others have been successful securing these components to not work loose under rapid semiautomatic fire (20 rds/ min). Thanks in advance for your help.

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11 years 1 month ago #31472 by Sharkey
Interesting issue Bollox but one I have no insight on since everything I own has the A-frame front site post so I've never messed with the gas blocks at all.

Have you checked with the manufacturers of these components and looks for FAQs about installation? Perhaps there is some insight there as to adjustments you can make as to how you have them secured.

Otherwise, I'm sure one of our more experienced guys with these parts will be here with some insight before long...

Good luck...

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11 years 1 month ago #31475 by jtallen83
My first question would be are they all ArmaLite components? If they are then I'm thinking you have a valid warranty issue for the pros to fix. Short of that I've never had the issue but only have a gas block mounted sight and don't use the carry handle. It sounds like you've went through the steps I could think off.......hopefully someone will have a fresh idea for you.

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11 years 1 month ago #31502 by OleCowboy
This is not rare and generally the result of older or well used iron sights. In fact I have encountered this myself. Couple of approaches:

Remove sight, disassemble what you can, clean well and put it back together taking note of any worn areas, rounded corners etc on sight and on weapon. Look closely maybe using mag glass to do inspection. If it still will not hold you will need to move to new sights. Putting on Loc-Tite etc is only a bandaid and a lot of trouble.

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11 years 1 month ago #31511 by 13fcolt
I'm with JT on giving armalite a call. If you are like me though and would rather DIY it then go with OC's suggestions.

I'm not familiar with the sight itself so I can't offer much. sorry.

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11 years 1 month ago #31516 by bollox

Sharkey wrote: Interesting issue Bollox but one I have no insight on since everything I own has the A-frame front site post so I've never messed with the gas blocks at all.

Have you checked with the manufacturers of these components and looks for FAQs about installation? Perhaps there is some insight there as to adjustments you can make as to how you have them secured.

Otherwise, I'm sure one of our more experienced guys with these parts will be here with some insight before long...

Good luck...


Thanks everyone for the comments. All components are OEM. I have not been able to find any Tech Notes except that calling for 60 in-lbs on the gas block screws. Emailed Armalite yesterday evening. I was less explicit on the problems but did mention them in the context of asking the price to convert the rifle to a pinned FSB.

I'll keep y'all posted.

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11 years 1 month ago #31519 by Sharkey
Try sending MrRaley a private message Bollox. He is our resident armorer and "IN" with Armalite (so to speak) and could be of GREAT assistance on this.

He hasn't been on much lately but I'm sure if you send him a PM, he'll get it and respond with some solid answers for you.

Good luck and please, don't forget to let us know any progress with these issues so we have it for the future and anyone else that may experience the same kind of thing... :)

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11 years 1 month ago #31533 by MrMarty51
:eatingpopcorn: :cowboy: :eatingpopcorn: :cowboy: :eatingpopcorn: :cowboy:

Waiting, listening, :whip: :wave: :cowboy:

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11 years 4 weeks ago #31596 by Lizardette
I'm not sure, but I think part of the problem with the front sight working loose may be heat transfer from the barrel to the gas block. Blue lock-tite in particular does not hold up well to heat. Red lock-tite may be better, or perhaps another product like Rock-Set (which I think actually holds up at higher temperatures). Before you go that route, check the threads. If they are stripped from being over-tightened (easier to do when the threaded hole is in aluminum), then no adhesive by itself is going to help.

If the the gas block has moved, that's a bad thing. You mentioned finding torque specifications for the screws on the gas block. Did you check to see that they were torqued correctly? Keep in mind, that if it is installed incorrectly (or out of spec), you'll likely find evidence of gas leaking out from under the gas block. You'll also probably be having reliability issues, particularly in extraction and ejection, because not enough gas is getting back to the bolt carrier. That's a problem I'm having with my LR-308, actually. If that's the case for you as well, it may be best to hand the problem to a professional. I can probably give you directions on realigning the gas block with the gas port if you want to do it yourself. Just let me know.

As for the carry handle, probably the easiest thing to do is make sure that you slide it as far forward on the rail as you can before tightening it down. Heat transfer from the receiver shouldn't be a problem, since it doesn't get near as hot as the barrel. Adhesive on the screws may help, if there's enough contact between the clamping surfaces and the rail on the receiver. If the carry handle has been moving, there should be marks on the rail and/or the clamping surfaces of the carry handle where the finish has rubbed off. The marks will not likely be uniform along the length, only showing the high spots. If you decide to remove some metal in order to fix this, remove it from the carry handle. It's much cheaper and easier to replace. Again, I can probably give you some directions if you'd like. Let me know.

ps: A friend of mine pointed something out while I was writing this. It may be worthwhile to mount a scope and see if the problem goes away. It would eliminate the rest of the rifle as a variable. I suspect that since the sights are definitely moving that it's unlikely anything else is wrong, but she thought I should mention it anyway.

Good luck, and I hope this has been helpful.

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11 years 4 weeks ago #31611 by mrraley
on the inside of the thumb screws, there should be nylon washers.

Are the washers present?

have you done any other modifications to the rifle?

can you post pictures of the sights?

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