Upper Receiver to Barrel Nut Thread Tightness - Does it matter at all?

[Leicafan1990]

Sometimes you get a barrel nut that has a pretty tight fit with the upper receiver threads (no play, you need to use a bit of force to thread the barrel nut all the way) and other times you get a barrel nut that threads on super easy and wiggles around on the receiver threads until it tightens up against the barrel extension lip.

Does the tightness of the thread fit between the upper receiver and barrel nut matter at all if you are trying to squeeze the most accuracy out of your AR?

I’m curious if barrel nut with loose threads (but is properly torqued) is more likely to cause rail deflection or barrel harmonics issues?

Does the presence of Aeroshell grease on the threads make this whole topic irrelevant?

I don’t think I’ve ever seen this topic discussed.

 

[USK308]

I just finished building my 8.6BLK SBR. The barrel nut on this rifle was probably one of the best fitting barrel nuts I have put on any of my AR platform rifles. Excellent threads and a solid fit meant that when I torqued to 35ft-lbs, I had full surety that the barrel wasn't going anywhere (thus [hopefully] ensuring good accuracy as a whole).

From a pure engineering perspective, when you have quality threads that ensure good fit between upper and the barrel, I do think that will enhance accuracy, but that is just the opinion of this old geezer [lol].

 

[johnnyvw]

I would try a different barrel nut (or two) to see if it fits better. Like anything else mass produced, there's no guarantee the threads are correctly made.

I would think the fit between the barrel extension and the upper would have more of an effect...

 

[longshot2000]

It is hard to say, given your description, and we are not there observing. As a rule, you want a pretty snug fit of the barrel extension into the receiver. Some receivers and some barrels are known to be loose, like Colt and FN military, which is needed due to dirt in the field. Some are super tight and need to be thermofit (fancy way of saying applying heat to one and cold to the other). The barrel nut should thread on relatively easily until it is time to tighten, and to that point, you should be using a fair amount of force to seat the barrel nut. If it is too tight, and does not hand tighten to the point it needs a long breaker bar armorers wrench, then there is likely a thread problem. Not the end of the world, but an out of spec receiver or barrel nut. I prefer antiseize grease with a copper base, as you are linking up steel and aluminum, and you should have a third metal to prevent a galvanic seizing, but many will use a standard grease. In theory, that is not a good idea, but in practice, many manufacturers use it and it seems to work.

The other part is whether your receiver is square to the barrel extension. This is seldom checked, but if you have time, it is a nice touch to get the receiver face squared with a mill. Most quality barrels and receivers are "good enough" and the degree to which the barrel is not inline with the receiver can be corrected with the iron sights and scope, so that you are aiming correctly straight, even if the bullet trajectory is not.

 

[papershredder]

No it shouldn't affect accuracy, the id flange of the nut is what mates up against the OD flange of the barrel extension, the threads are there to hold the two pieces together. With that being said, if the nut is too loose, I would get a different nut. Even when torqued, an oversized nut has a greater potential to come loose. Which would affect accuracy once the nut starts backing off. A lack of thread engagement at the most pressurized point of your rifle also carries potential safety issues as well.