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M2 Carbine Rear Sight


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I've had two (semi auto) carbines where the rear sight worked itself loose. First was an Ibm and second was a Saginaw. It was suggested to me that you could fix it either by removing the sight and peening the top of the receiver with a hammer or by cutting a small shim out of a soda can and placing it under the sight when you insert it. I did it for the IBM and it worked fine accuracy was within normal limits for a carbine. the Saginaw I haven't messed with yet.
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Thanks to those who have commented thus far. Hopefully others will join in.

Reason for asking.----

A member on this board and also a TCA member recently bought an M2 carbine. Its a Saginaw over stamp.

After doing a fair amount of full auto firing the rear sight became very sloppy and could be pushed out of the dovetail with no effort.

He came to me for help and I sorted thru a box of carbine sights and selected one that fit the tightest. I had to pound it in with a brass rod.

He returned a while later with exactly the same problem.

This time I inserted a shim .0015 thick and again drove the sight on with a brass rod.

Yesterday , at a steel plate shoot, the exact same thing happened, this time while I was shooting the carbine.

This has got me baffled. It appears the dove tail is stretching. A scary thought since the receiver appears to be overstressed.

Increasing the shim thickness without knowing what is going on doesn't seem to be the answer.

Any ideas what is happening here??

Jim C

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What ammo is he using and has he change the op rod spring lately? Check the back,inside of the receiver for peening from the bolt hitting it.

As for ammo, if reloads, they might be too hot for the op rod spring that is installed or the op rod spring is weak.

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The type II and type III sights are in fact supposed to be staked. The staking is heavy and was done inside the sight. The sight was moved all the way left, staked on the right side front and back. The staking went through the dovetail of the receiver and deformed it into the sight, then the sight was moved all the way to the right and the process repeated. Without staking the sight will come loose.

 

There is a special tool to press the sight in and the sight should only be able to be inserted from the right to the left. As the dovetail goes left it does get narrower making the sight get tighter as it goes left and should bight down roughly center. If it goes all the way though the left side then the receiver is out of spec.

 

I can pull some of my carbines out with the type I sights tomorrow that I can still access the female dovetail and take measurements with a micrometers of that will help you. I doubt that the receiver is stretching, but I've been wrong many times before.

 

The receiver peening that I mentioned before isn't something I made up, it is in the ordnance technical manuals and if you want I can look for a page number tomorrow. I was not comfortable doing this because in the ordnance manual it says something as simple as 'peen the top of the receiver dovetail with a hammer to tighten a loose sight'. My overthinking self doesn't know how hard or how big of a hammer to peen it with and am paranoid about doing damage.

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Let's stay focused on the problem at hand and not get lost in the weeds.

I have a TM and I am aware of the HEAVY staking of the sight. Previous owners staked it so heavy that there is no metal remaining for staking.

I have owned carbines for the last 55 years and have been changing sights and shooting them for all those years. I've never owned and will never owned a sight removal tool. I use a brass or aluminum rod.

The problem is , what caused an already installed sight to become loose from shooting.

Why would a sight , that had to be pounded on, be easily moved back forth with only fingers.

N64 is probably on to something with the weak spring idea. I'll ask the owner to check its length. Also I'll try to find out about the ammo.

Thanks for the comments.

Jim C

Edited by jim c 351
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Some things that have worked in the past .

Blue loctite in the dovetail gaps .

Punch dimple the dovetail groove that rests under the rear sight .

Disassemble the rear sight and drill and tap one or two set screw holes with minor drilling on the reciever for the set screws to grab .

The above two were used on factory 03A3 rear sights to get them to stay on .

Drill a small hole through the sight and the reciever to put in a small pin . You could do this with a blind hole , but then you'd have to drill out the pin to remove the sight ....but how often do you need to do that ?

Chris

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Oh , do NOT try to pound down the upper edges of the dovetail on this rifle . The metal is very hard and brittle . Ok to punch , but not wide spread hammering . Remember all those people who tried to pinch the two legs together to hold the triggerhousing tighter ? Remember all those recievers with a broken off or rewelded ( ok , welded ) leg ? Enough said.

Chris

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I would guess that the staking was not good enough or the dovetail cut in the reciever was a tad too big or the rear sight dovetail too small , allowing movement , which led to battering , which led to more movement ....on and on till the movement was great enough to be noticed.

I don't for a moment think that a reciever would streach through that area....too thick and no pressure .

Chris

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  • 2 weeks later...

Jim-

 

I just replaced a carbine slide on a friends M1 Carbine and noticed that the rear sight was very heavily stalked. I did comment that the op rod spring felt weak when I looked at the M2 in question. I wonder if it is being caused by excessive recoil and battering the back of the receiver-causing it to loosen up?

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John & Atlas 64,

Last week I got another chance to work on the carbine.

The operating slide spring was 3/8 inch below specks and the shooter was shooting gunshow reloads.

SO- following atlas64 advice I installed a proper length spring and advised owner to shoot only factory ammo.

I filed another staking notch on the rear sight, and using the .0015 inch shim and double coating of Loctite & I restaked the sight.

Suggested owner consider buying a new Wolfe spring.

Now we can just hope for the best.

Again,--thanks to all who replied.

Jim C

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