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I'm building my DPMS 308, and ran into an issue with the barrel nut. This is an Aero upper and barrel and the nut won't index to the gas tube orifice properly.

This is hand tight:

20220819_200011.jpg

This is torqued to 36 ft lbs

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I've tried starting it several different ways but since the threads are aligned one way it seems sort of hopeless.
 
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We used anti-seize because the threads were so tight at first. These barrel nuts stretch? Can they be reused when changing barrels?
The nut itself doesn't actually stretch, but the fresh threads of the nut and receiver will. They will start to stabilize and stretch less. It's considered by many to be standard procedure to season the barrel nut, usually 3 times.
General tips: Don't use a torque wrench to loosen fasteners/nuts unless it's designed for that. Keep an eye on the clearance between end of the nut and the receiver, sometimes you can be torqueing against the receiver instead of the barrel extension flange. That's usually from something being out of spec.
 
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Can they be reused when changing barrels?
Msgriff pretty much covered it all, yes.... you can reuse a barrel nut if you choose to swap barrels. You would still want to repeat the seasoning process after a barrel swap though, even with the same nut and upper receiver. Just not as agressively on the first 2 passes.
 
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I gave it a few good cranks after loosening each time. I assume it may be good practice to check torque after shooting it for a bit?
As long as your torque values are within specs during assembly it's not necessary. Visual inspections are certainly recommended, but any real shifting out of alignment will be readily apparent without having to put a wrench to it.

At least, I don't. I think it can hurt more than help to be fudging with your threads and repeated disassembly and reassembly of other components (like your handguard) may cause fit and wear issues.
 
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The shims worked great. Torqued it to about 50 ft lbs.

I ran the GO/NOGO gauges through it and the GO is super tight. I can't actually force the BCG onto the gauge with my hand. I can tap it down with a small, non-marking hammer and it closes on it. Is that too tight or not unexpected for a new BCG and barrel?
 
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The shims worked great. Torqued it to about 50 ft lbs.

I ran the GO/NOGO gauges through it and the GO is super tight. I can't actually force the BCG onto the gauge with my hand. I can tap it down with a small, non-marking hammer and it closes on it. Is that too tight or not unexpected for a new BCG and barrel?
You could try it with a stripped bolt. No extractor or ejector. If it doesn't close under normal operation then you may have a bit of an issue. I would also examine the chamber lugs for any burrs or deformations. If nothing is obvious then I would use just the bolt to rotate it into battery manually and see if you can "feel" any type of abnormality.

If it chambers fine with a go guage and stripped bolt face, I would say you're fine.
 
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The shims worked great. Torqued it to about 50 ft lbs.

I ran the GO/NOGO gauges through it and the GO is super tight. I can't actually force the BCG onto the gauge with my hand. I can tap it down with a small, non-marking hammer and it closes on it. Is that too tight or not unexpected for a new BCG and barrel?
As stated above you want to strip your bolt before checking headspace.
And never let a BCG fall on a headspace gauge.
 
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In general the bolt should be stripped prior to checking headspace?
Ideally, Yes. Even though it may not be noticeable to the naked eye, the ejector is applying pressure to one side of the guage and the extractor in contact with another that can produce a false result.
 
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In general the bolt should be stripped prior to checking headspace?
My opinion, yes. There are some .223/5.56 gauges with a cut-out for the ejector or modified so the ejector doesn't need to be removed. With mi-spec AR-15 bolts, the ejector is always in the same location. AR-10/SR25/AR308 bolts, especially those with dual ejectors, are not standardized. These bolts can be more difficult to disassemble/assemble compared to the AR-15 bolts. They make tools/jigs for compressing the ejector(s), or some make their own. I check headspace before installing the barrel with the stripped bolt and gauges using nothing but my fingers.
 
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I broke down the bolt, and was able to perform the tests with the gauges on the barrel, both by hand and installed in the BCG (minus the extractor and the ejector). Thanks for all the pointers.
 

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