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Discussion Starter · #1 ·
I have been struggling to get my 556 to hold zero and I think I have now found out why. My front sight had a little play in it, obviously not a good thing so I just pulled it and measured the width of the dovetail on the sight and it was .573 in width, then I measured the width of the dovetail on my front block and it was .598. I am no engineer but 25 thousands seems like a fair amount of play for a front sight.

So the question is, do I just need to get another front sight and hope that it is the proper width? Obviously I will mic it before I buy to make sure but are there any other options anyone can think of before I plop down another c-note+ on a new front sight, again.
 

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It depends if the sight is tight after tightening the mounting screw.
If it is, sounds like the screw is getting loose as you fire the rifle. Some loctite on the screw should fix the problem.
If it's still loose after tightening the screw, call MI for a replacement since the sight has a lifetime warranty.
 

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Discussion Starter · #3 ·
I don't think I did a very good job of explaining. Even with the screw tight, the sight can move slightly from side to side since its dovetail is not as wide as the slot on the gas block.

Maybe a pic will help, as you can see, there is a slight lip on the gas block where the sight does not completely cover, it is flush on the other side.
 

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Since it's loose even with the screw tightened, sounds like you got a defective sight.
Call MI, you should be able to get a replacement no problem.
 

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Are those front sights on the same plane as Mil spec AR sights or they regular Popsicle back sights that comes with a SIG?

It looks like the back of the gas block might be cracked. Its hard to see.
that could couse some movement.
 

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Discussion Starter · #6 ·
Gas block looks fine, at least to me with a bright light, I think that may be an tool mark or something brought out by the flash. I took the front flip up sight off to mount that one.

I sent an e-mail to MI this morning. My biggest problem is that I need my rifle ready for next weekend to take a class in Houston. I guess if I had to I could try to find the flip up I took off and go with that for now, but I really do prefer the MI sight.
 

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Discussion Starter · #7 ·
Just a quick update.

Midwest Industries is one of the best companies I have ever had dealings with. I sent them an e-mail this morning at 0530 central time and had a response within 30 minutes. Troy and I exchanged a few e-mails trying to figure the issue out with no luck. Without any prompting from me he asked for my address and is sending me a new one out to see if that fixes the problem. I have decided that if they make it for my rifle and I want it, the first place I will go will be them, they obviously place a lot of value on customer happiness.
 

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kutter said:
Just a quick update.

Midwest Industries is one of the best companies I have ever had dealings with. I sent them an e-mail this morning at 0530 central time and had a response within 30 minutes. Troy and I exchanged a few e-mails trying to figure the issue out with no luck. Without any prompting from me he asked for my address and is sending me a new one out to see if that fixes the problem. I have decided that if they make it for my rifle and I want it, the first place I will go will be them, they obviously place a lot of value on customer happiness.
I had an issue in the past with MI and had the same experience. Immediate response, replacement, follow up. By far THE BEST company I have dealt with for Customer Service.
 

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FWIW I had the exact same problem with my MI sight on my older SWAT rifle that I got rid of a year ago. Had the MI on there for a while and when I went to remove it to put the original HK style sight back on, I noticed the MI sight was very loose in the dovetail slot. Not sure how it loosened up, as I had not used the rifle much before I sold it. I included the MI sight with the rifle when I sold it so I have no idea if the new owner ended up using it or not.
 

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I just got my 556 and it already had a MI flip up sight and mine is loose as well. I figured I'd just take a feeler gauge and get the right gap then cut a shim out of a junk feeler gauge to take up the slack. I may try to contact MI first to see if they will exchnage my sight even though I"m a second owner
 

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Old thread but I'd like to mention my MI is loose as well but it doesn't bother me. Why?
When you removed your OEM sight, or when I did, I noticed it felt very tight, but the key wasn't tight, I was experiencing tension as I drifted it out. The base of the sight has a cut between the dovetails. This allows the key to spring. There is a difference between tight and tension, which is dynamic. As the gas block heats up and expands the Sig sight base key is flexible to accommodate that expansion, otherwise the gas block might crack. There are other good reasons for the tight key but I believe this to be relevant. If MI were to try to make their sight key too tight, a few problems can occur they don't have to deal with if they just give it enough tolerance to begin with. If you are an iron sight shooter and the movement is an issue, I can see dealing with it. For the BUIS people whose MI will remain as a BU only, I say install with some locktite and forget it. I don't know if anyone ever got a MI folder that was snug, but if they do exist, I would work with MI to get one, they are great sights. Mine is a tad loose too. I think I will use some brass foil to shim it a little, but for the reasons stated above, I'm glad its not really tight.

 

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The reason why the MI sight pictured above is both loose and not centered is the square nut is missing that comes with the sight. Needs to be installed with Loctite.
 

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The reason why the MI sight pictured above is both loose and not centered is the square nut is missing that comes with the sight. Needs to be installed with Loctite.
I think Kutter left it off to show the dovetail
 

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Oh. Post is very old I see, along with degreasing the threads do the dovetail too and fill with Loctite - it will not move.
 

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Personally if I have to use loctite to hold a part on my rifle, there is something wrong. I don't Loctite ANYTHING on my weapons.
 

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Sorry to hear that banshee. Loctite is used on most firearms from the factory just for starters. May want to educate yourself some before throwing out a statement like that.
 

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Personally if I have to use loctite to hold a part on my rifle, there is something wrong. I don't Loctite ANYTHING on my weapons.
I like this view point. Yes, many parts are loctighted, it is a common practice. But is it a really good fastener technique? When there are better options, no. I would say Loctite is easy to use and acceptable on non-critical parts. Lets use an extreme example, the axle nut that holds your car wheel on. Nobody would Loctite that. One good reason is there is a standard securing method of castellated nut and cotter pin there to prevent rotation. On aircraft and race cars many fasteners are drilled and secured with safety wire. Anti-rotation washers, roll pins and staking. The issue comes down to cost and ability. Many fasteners on a firearm are just too small to integrate anti-rotation parts, and many end-users wouldn't have the skill or tools to apply them. The solution, Loctite! What's Its melting point?
 

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Thanks for the info lamsotticus. Loctite comes in all temp ranges and in gap filling formulas. I work in aircraft and used to work in automotive, things like nuts on differential drive pinion use only Loctite. Many fasteners on aircraft use it to. It just flat out works.
 
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