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-to...ping-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.