Barrel extension shims?

[grottulf]

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?

 

[mscott]

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.

[mpom]

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.aspx, https://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 March 28, 2021 by mpom
added link

[grottulf]

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...

 

[Chip3]

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.

[TonytheTiger]

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.

[CharlieD]

You can buy stainless shim stock from McMaster carr, perhaps try .0015

[grottulf]

I've gotten my hands on a sheet of stainless .001" stock now, so I'll cut out a new shim. 

I'll just have to find the time for it... 

 

[ltdmstr]

Aero-Precision sells .001 barrel nut shims.  https://www.aeroprecisionusa.com/ar15-bar-shim-pack

[mpom]

12 hours ago, ltdmstr said:

Aero-Precision sells .001 barrel nut shims.  https://www.aeroprecisionusa.com/ar15-bar-shim-pack

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

 

Mark

[ltdmstr]

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.

[wheelie]

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.

[grottulf]

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...

 

 

 

 

 

[K-Tex]

On 3/25/2021 at 3:25 PM, grottulf said:

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?

 

There are shims out there.   They are used for gas tube barrel nut timing.   When torquing the nut delta rings can misalign making the gas tube difficult too fit into the upper receiver.   The other without delta rings (barrel nuts with handguard screws) sometimes need too be shimmed for proper handguard alignment.   AR15 and AR10 use different size shims.   Check with a gunsmith and see if they have them in stock?

[grottulf]

11 minutes ago, K-Tex said:

There are shims out there.   They are used for gas tube barrel nut timing.   When torquing the nut delta rings can misalign making the gas tube difficult too fit into the upper receiver.   The other without delta rings (barrel nuts with handguard screws) sometimes need too be shimmed for proper handguard alignment.   AR15 and AR10 use different size shims.   Check with a gunsmith and see if they have them in stock?

The barrel nut shims are bigger, I needed a shim between the barrel extension and the barrel.

But it's solved now anyway.

 

[K-Tex]

29 minutes ago, grottulf said:

The barrel nut shims are bigger, I needed a shim between the barrel extension and the barrel.

But it's solved now anyway.

 

Yes that is where they go.   Glad it's fixed!   Bigger or thicker?   Oh well, never mind it's fixed.

[kurtm]

I'm pretty sure that the barrel extension is that little notched thingy at the back of the barrel that the bolt locks into and has those feed ramp cut thingys. It is screwed on to the back of the barrel to the tune of 135-150 ft/lbs. In the olden days if an M1 or M-14 barrel didn't torque up and time correctly, they had a fixture that had three big rollers that could be tightened around the shoulder of the barrel and then the barrel was rotated effectively swaging a bit more material into the shoulder area so it could reach torque and timing kind of like the punch idea someone suggested. Now that said I have also had a barrel back off from the extension and I red lock-tited the crap out of it without a shim and shot another 4-5 thousand rounds out of it with no problem, so I would think your fine.

Also I'm pretty sure a barrel nut shim fits under the barrel nut on top of the shoulder of the extension which is that little ridged thingy with the alignment pin sticking up out of it. It would never work as a barrel extension shim. It might help align a hand guard/ gas tube, but it is not going to shim the extension.

[Silver_Surfer]

Dam what a nightmare! I wish I never seen this thread. I've got so used too using my reaction rod or upper receiver clamshell blocks(PCC) to change out my muzzle devices. I never thought about the barrel unscrewing from the extension.  I'll be dusting off my barrel blocks when I get home. 

[K-Tex]

12 hours ago, kurtm said:

I'm pretty sure that the barrel extension is that little notched thingy at the back of the barrel that the bolt locks into and has those feed ramp cut thingys. It is screwed on to the back of the barrel to the tune of 135-150 ft/lbs. In the olden days if an M1 or M-14 barrel didn't torque up and time correctly, they had a fixture that had three big rollers that could be tightened around the shoulder of the barrel and then the barrel was rotated effectively swaging a bit more material into the shoulder area so it could reach torque and timing kind of like the punch idea someone suggested. Now that said I have also had a barrel back off from the extension and I red lock-tited the crap out of it without a shim and shot another 4-5 thousand rounds out of it with no problem, so I would think your fine.

Also I'm pretty sure a barrel nut shim fits under the barrel nut on top of the shoulder of the extension which is that little ridged thingy with the alignment pin sticking up out of it. It would never work as a barrel extension shim. It might help align a hand guard/ gas tube, but it is not going to shim the extension.

It goes like this!   Receiver, barrel,shims then nut in that order.   So shims tighten between the extension and the barrel nut!

[K-Tex]

11 hours ago, Silver_Surfer said:

Dam what a nightmare! I wish I never seen this thread. I've got so used too using my reaction rod or upper receiver clamshell blocks(PCC) to change out my muzzle devices. I never thought about the barrel unscrewing from the extension.  I'll be dusting off my barrel blocks when I get home. 

Using a reaction rod is easier on the receiver.   It keeps the receiver from twisting/torquing.   Use some anti-seize on the receiver threads.

[grottulf]

1 hour ago, K-Tex said:

It goes like this!   Receiver, barrel,shims then nut in that order.   So shims tighten between the extension and the barrel nut!

Read what Kurtm wrote again.

A barrel nut shim is only for indexing the barrelnut (and thereby some handguards)

[grottulf]

1 hour ago, K-Tex said:

Using a reaction rod is easier on the receiver.   It keeps the receiver from twisting/torquing.   Use some anti-seize on the receiver threads.

It doesn't help against the barrel extension coming loose.

Always use a barrel vise when you're loosening a muzzle device.

Learn from my mistake.

[K-Tex]

24 minutes ago, grottulf said:

It doesn't help against the barrel extension coming loose.

Always use a barrel vise when you're loosening a muzzle device.

Learn from my mistake.

I can agree on muzzle device removal.   How tight was the muzzle device.....seems excessively tight?   Best wishes!

[K-Tex]

32 minutes ago, grottulf said:

Read what Kurtm wrote again.

A barrel nut shim is only for indexing the barrelnut (and thereby some handguards)

How do you think it's headspaced?   The extension is used for headspacing the bolt, then a hole is drilled in the extension for gas port to dowel alignment.   There could be another way?   I've never tried too remove an extension too see if the pin/dowel goes into the barrel enough so the extension doesn't inadvertently unscrew.   Maybe my next project!

[kurtm]

So K-Tex, are you saying you can change the head space on an AR with a barrel nut shim? That is what you just said above, you need to revisit how it all goes together if you think this.

The extension is screwed on to the barrel, the barrel is headspace to the extension and torqued to around 135-150 ft/lbs, no nut involved! The extension comes with the pin hole already drilled it IS NOT drilled latter. The extension is the part that fits into the upper receiver, not the barrel, so it really goes like this.... receiver, extension, barrel (already screwed on to extension and headspace), shims....if needed (almost never by the way), and then barrel nut. Here is a picture of an extension waiting for a barrel to be threaded, chambered, headspaced, and screwed on.

Edited October 15, 2021 by kurtm