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I have some questions for you gunsmiths out there. 

 

I tried to loosen my comp the other day, and managed to get the barrel extension loose.

It didn't take much force at all, so 

I guess it wasn't torqued to specs from the factory...

So I've learned the hard way to always use a barrel vise when removing a comp 😳

 

Now I'm trying to get it back on the barrel with the correct timing and torque. 

Turning it until it lined up, obviously didn't take enough torque...

So I turned it until I got a satisfactory torque reading, and measured how many degrees past the pin it had turned.

It was 14 degrees off, and with a little calculations I found that I need a .001" shim to get it right. 

 

I tried to Google it but couldn't find any shims for this?

Does anyone sell these kind of shims, or do I need to cut it out myself from a sheet?

If so would it be better to get a 0.001" steel shim, or should I use a slightly thicker brass shim, and allow for some deformation?

 

And regarding the torque, my Midwest upper receiver rod was beginning to feel sketchy when it got over 135 ft-lbs. 

But I'm thinking that if I use permanent thread locker, it should be enough with 135...

Or will it be too hot for thread locker?

What do you think?

 

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Never heard of shims for barrel extension. If it were mine I would just clean the threads up really well and put it back together with red loctite or rockset and call it good. Of course my free advice is just that and to be followed at your own risk.

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Sounds like you neeed to make a shim to take up the space, thus achieving reasonable torque between the barrel and barrel extension, prior to installing the pin. There are shims available for shimming barrel extension to front face of upper receiver, don't know if the dimensions match what you are seeking https://www.brownells.com/rifle-parts/barrel-parts/rifle-barrel-hardware/washers/barrel-nut-shim-kit-prod96013.aspxhttps://www.brownells.com/rifle-parts/barrel-parts/rifle-barrel-hardware/washers/barrel-nut-shim-kit-prod96013.aspx

 If not, 0.001 stock is very thin, can probably be cut with sharp scissors, just prone to bending and tearing, may want to use weak glue to attach to thick paper prior to cutting it to shape, so its easier to control.

Let us know how it goes.

 

Mark

Edited by mpom
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I have barrel nut shims but those are larger.

I got my hands on some .001" brass foil, and made my own shim yesterday.

But when I tried mounting it again today I only reached 80 ft-lbs when it reached the correct timing...

When I disassembled it again I saw that the shim had cracked.

I think brass is too soft, so it probably compressed under the load.

I'll try to find some stainless steel foil instead...

 

20210327_152812_copy_756x1008.jpg

20210327_154643_copy_1209x1612.jpg

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  • 2 weeks later...

https://www.wingtactical.com/firearm-parts/ar-15-parts/muzzle-devices/strike-industries-5-8-24-muzzle-device-alignment-shim-kit/ have ordered form these guys before with good results. Not a huge strike industries fan but probably hard to mess up shims

 

Have a jamb nut on a no name comp and prefer that.

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7 hours ago, Chip3 said:

https://www.wingtactical.com/firearm-parts/ar-15-parts/muzzle-devices/strike-industries-5-8-24-muzzle-device-alignment-shim-kit/ have ordered form these guys before with good results. Not a huge strike industries fan but probably hard to mess up shims

 

Have a jamb nut on a no name comp and prefer that.

That's not what's being discussed here.

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1 hour ago, mpom said:

I believe the OP is trying to shim the barrel extension onto the barrel, so barrel nut shim will not work, different dimensions.

 

Mark

 

Woops.  Sorry about that.

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  • 3 weeks later...

Lightly peen (a series of slight punch marks around the face) the face of the barrel extension where it mates up to the shoulder on the barrel. Apply a generous amount of Loctite 609 to the threads, screw it together perfectly indexed and reassemble the barrel to the receiver the next day.

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7 hours ago, wheelie said:

Lightly peen (a series of slight punch marks around the face) the face of the barrel extension where it mates up to the shoulder on the barrel. Apply a generous amount of Loctite 609 to the threads, screw it together perfectly indexed and reassemble the barrel to the receiver the next day.

That's not a bad idea 🤔

 

I've fixed it now though.

I made a new shim from 0.001 stainless steel stock.

First I test torqued it with oil and I got it to around 100 ft lbs.

I deemed that to be enough as long as I add permanent threadlocker.

 

 

When I applied a threadlocker, I applied it not only to the threads, but to both sides of the shim as well, for lubrication.

(I noticed that shims this thin breaks easily otherwise, at least if they're home made 😳)

But then I couldn't rotate it enough to get it to align...

 

I hadn't considered that the  threadlocker takes up some space as well.

 

So I ended up removing the shim (and cleaned the threads thoroughly)

And re-tightened it without the shim, and just thread locker, on both threads and the mating surface.

It was enough to get just under 100 ft lbs.

 

I think (hope) that will work fine.

I'll never remove a comp without a barrel vise again anyway...😳

 

 

 

 

 

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