Barrel nut help

[rxer311]

So I have been trying to install my SMOS rail to my SMOS upper receiver and I am having trouble with my timing. I am using a Magpul Bev Block and a large 1&1/16" wrench (no torque wrench).

When I install my barrel nut hand tight it actually lines up perfectly where it should. I am having trouble getting it torqued down because it will require an excessive amount of torque to get me to the next hole. As I said I am not using a torque wrench, however, I do know that hand tight is not 30 ft lbs and I know that just getting halfway to the next hole is requiring more torque than what I am comfortable with. From all my years wrenching on cars I have come to get a general idea of about how much torque I am using. I am sure that I am not getting to 80 ft lbs getting to halfway but I am using a significant amount of force to get there. I don't foresee being able to get this timed at the next hole.

Should I call SMOS and see if they can send me a different barrel nut? Should I just leave this barrel install to my gun smith? Anybody else have any tips for installing this style barrel nut?

Thanks.

[alamo5000]

Torque it and back it off in small increments? Make sure you have it greased on the threads.

[rxer311]

I have done this many times. I have torqued it and backed off in small increments many times. All of my threads are greased. This one may be one I have to defer to my gun smith and see if he can get it timed within spec.

[alamo5000]

Maybe check your barrel extensions and see if that's good.

If you have a different barrel to try experiment some.

[alamo5000]

Speaking of that make sure your extension is seated properly with no barrel nut.

If it's just a sheer tight fit then try putting the upper in the oven at 250 for a while.

Pics would help here I think.

[SINNER]

Either take a couple hundredths off the face of the receiver in a mill or shim the barrel nut. Clearly the mill is the preferred method but it's out of reach for most.

[alamo5000]

Either take a couple hundredths off the face of the receiver in a mill or shim the barrel nut. Clearly the mill is the preferred method but it's out of reach for most.

If you're sanding why not sand down the nut itself? That way if you're like me provided it gets messed up you can buy a new nut and be done with it.

[alamo5000]

Before you start sanding though does the nut go on the upper freely without the barrel?

[BoilerUp]

Option 1) Shim set: http://bisonarmory.com/ar-15-barrel-nut-shim-set/

Option 2) lap the receiver face http://pacifictoolandgauge.com/ar-tools/1139-ar-15-upper-receiver-lapping-tool.html but that still may not get you there and I wouldn't recommend lapping more than required to true the receiver which means you still may need to use option 1.

Option 3) get another barrel nut and see if luck is on your side (i.g., counting on the threads starting in a different position)

Option 4) (my preference) stop buying handguards that require timing of the barrel nut

[rxer311]

Thank you for all of the help. I think I am going to stop by my gun smith tomorrow and see if he can get it timed within spec. If not I am going to order some of those shims.

[JGifford]

Honestly? Buy a torque wrench. I'm not trying to be a dick, but you're talking about sanding critical bearing surfaces before you have even quantified the problem. Try and see exactly how much torque you really are applying.

[Joelski]

Good decision; live to fight another day.

To me, shims are the only way to go in this circumstance. The up/down tension method is going to introduce distortion somewhere in the structure of the barrel to receiver junction, that's just simple mechanics. It might work for a degree or two at most, but I wouldn't want to risk damaging my rifle in order to get a fit today when I can time it with shims later.

And yes; you shouldn't risk damaging your investment, or improper assembly by not using a torque wrench. That's as fundamental as checking headspacing once the barrel is properly torqued to spec.

[SINNER]

You sand wood.

When I say in a mill I mean correctly held square and true and cutting the face of the lower with a end cutting mill. Not sure how you would even sand inside the barrel nut.

[JGifford]

Speaking of that make sure your extension is seated properly with no barrel nut.

If it's just a sheer tight fit then try putting the upper in the oven at 250 for a while.

Pics would help here I think.

I only do thermal fit on barrels to uppers if I'm building. Heat gun for a minute or two directed from the inside of the upper out the front works. Once the two are seated (you do it FAST!, as the barrel pulls heat quick from the upper and it grips it with a quickness), two strong people won't be pulling them apart. Just a preference of mine, but I am a fan of details, and thermal fit is something I place value on.

[JGifford]

You sand wood.

When I say in a mill I mean correctly held square and true and cutting the face of the lower with a end cutting mill. Not sure how you would even sand inside the barrel nut.

Failing to have a true receiver face lessens bolt life and induces more harmonics. It's all around a bad thing.

[SINNER]

I bet $100 when I'm done with the mill it's more true and square to the carrier bore than 90% of the ones sold.

The biggest issue is when people go too far it will cause FTF's due to the barrel extension protrusion. M4 feed ramps are even more prone to issues.

[rxer311]

What? I was not even thinking about sanding.

[alamo5000]

Really though for the forum purposes... if you're going to take it to a gunsmith then that's up to you. Nobody is trying to persuade you otherwise. But from previous experience (here on WEVO) if you take a few photos and put them up we might be able to save you a lot or a little bit of time and money.

There are a lot of people here that have a lot of experience.

[Joelski]

Really though for the forum purposes... if you're going to take it to a gunsmith then that's up to you. Nobody is trying to persuade you otherwise. But from previous experience (here on WEVO) if you take a few photos and put them up we might be able to save you a lot or a little bit of time and money.

There are a lot of people here that have a lot of experience.

That, or you're going to get a bunch of contradicting information and nobody agreeing on how to fix the damn thing. I've personally never heard of "Thermal fitting" a barrell extension to a receiver unless it's to mate out-of-spec parts together. Properly spec'd parts should fit together with a minimum of nev r sieze moly grease and very little pressure. Sinner is correct that lapping the receiver face is the best solution to avoid adapting (Read: Making it fit) with shims. The shims are an accepted intervention among armorers, however.

Your choice: non-destructive lapping to square up the receiver face and remove several thousandths of material that shims would add, or simple add shims. Either will work. Either are accepted as primary remedies. The benefits of "Accurizing" are minimal to a less seasoned shooter and incorporate other expensive, esoteric measures that add to the cost, but not the gross performance return on investment.

[UWone77]

Shims or just ask for another barrel nut and swap it out.

Ridiculous advice given on this thread is rather embarrassing. The guy just needs to get his barrel nut timed...

[Mecha_Arms]

Seems like shims are the solution. I don't know what the barrel nut is on that rail, but any other time I've run into that problem, shims have been the answer.

[JGifford]

That, or you're going to get a bunch of contradicting information and nobody agreeing on how to fix the damn thing. I've personally never heard of "Thermal fitting" a barrell extension to a receiver unless it's to mate out-of-spec parts together. Properly spec'd parts should fit together with a minimum of nev r sieze moly grease and very little pressure. Sinner is correct that lapping the receiver face is the best solution to avoid adapting (Read: Making it fit) with shims. The shims are an accepted intervention among armorers, however.

Your choice: non-destructive lapping to square up the receiver face and remove several thousandths of material that shims would add, or simple add shims. Either will work. Either are accepted as primary remedies. The benefits of "Accurizing" are minimal to a less seasoned shooter and incorporate other expensive, esoteric measures that add to the cost, but not the gross performance return on investment.

Thermal fitting is what is spec'ed by some manufacturers. It just depends on how close you hold your tolerances and what you set the ID of the uppers spec to. I personally like it, although I have also heard that accuracy testing has not demonstrated quantifiable superiority over a simple slip fit.

[JGifford]

I still say OP needs to buy a torque wrench and try to properly install it first instead of just guessing like OP has been doing...

[rxer311]

I stopped by my gun Smith today and he got my barrel nut torqued and timed. He did need to use a shim. Best $10 I could spend to get it done right.

[SINNER]

Shims are a band aid for lack of equipment or ability IMO. Then again everyone with a set of punches and a torque wench is a gunsmith now a days.

[JGifford]

I stopped by my gun Smith today and he got my barrel nut torqued and timed. He did need to use a shim. Best $10 I could spend to get it done right.

I'm guessing he just lubed the threads and torqued it properly with the correct wrench vs. guessing?

[rxer311]

You missed the part where I said he had to use a shim.

[JGifford]

You missed the part where I said he had to use a shim.

I read it wrong, my fault.

[The Truth]

I just saw this but, if you are still having issues please call. We will do whatever we can to help.

[rxer311]

I just saw this but, if you are still having issues please call. We will do whatever we can to help.

No problem. Took it to my gunsmith and he was able to get it installed with a shim.

[Molon]

I just saw this but, if you are still having issues please call. We will do whatever we can to help.




Apropos to nothing (except torque[BD]), what torque setting do you recommend for the screws that secure the GFY handguard to the barrel nut, and which version of Loctite do you recommend for this application?


...

[alamo5000]

I just saw this but, if you are still having issues please call. We will do whatever we can to help.

I don't own any of your products yet, but the fact that you're here speaks volumes and puts you on my short list.

[inthegame]

I see pictures of SMOS rails that are not flush with the receiver, there is some empty space between the two. It can be to an SMOS upper or otherwise. I dont see it in all builds, but enough to be a concern to an ocd person. Is this something that I should expect if I purchase a GFY rail? Picture below shows white space im talking about.

1654

[Aragorn]

^^^Perhaps a result of shims being used to properly time the nut?

That'd be my guess.

[UWone77]

The "gap" is always going to be a possible issue with timed barrel nuts and shims.

[inthegame]

I dont think ive ever seen a Noveske NSR with this issue and its almost the same design. With that being said I think the SMOS GFY looks better then the Noveske Mlok. From the options posted in reply #10 of this thread. There is no mention of shaving down the barrel nut to get it to grab closer to the receiver. Or is this a no no. Most likely I will have a gunsmith put my upper together as I dont have some tools to complete the process. Just thinking ahead in case I have to live with the gap. Maybe ill think about it like a thigh gap and all we be well.

[alamo5000]

There is no mention of shaving down the barrel nut to get it to grab closer to the receiver. Or is this a no no.


Go back to post #7 in this thread.... :)

[fledge]

I have gaps on mine and I haven't used a shim yet. I think it's that way by design. I'm curious if someone has a pic of it NOT having a small gap. I'm OCD and the gap doesn't bother me.

[SINNER]

The barrel nut bottoms on the barrel extension, not the receiver. If you have the capacity to clearance the shoulder inside the barrel nut, you also very likely have the intelligence to figure out it is the worst solution possible when you can remove material from the exposed face of the receiver with 1/10 of the effort. For that matter it would even be easier to remove a few hundredths off the barrel extension flange than the inside face of the nut.

[inthegame]

I'll just leave it to the pros once I get to that point. I am outside of my scope of knowledge and experience

[rxer311]

By the way...Like I said, a shim was used on mine.

No Gap!

[JGifford]

Just a question, since you're here...would you mind sharing where you get your aluminum from, SMOS? Mainly, which country sourcers/certs it?