The sitch is that I’m going to be testing several barrels using the same upper receiver. I know that it’s a good idea to torque a barrel nut three times when installing a barrel. When you swap or replace a barrel, and assuming you’re re-using the same barrel nut, should you torque it three times again? Is it possible to eventually wear-out the upper’s threads?
Thanks!
Is it possible to wear out the threads? Probably. Will you do it by testing a few barrels? Probably not… someone with more experience may weigh in here, but as long as you’re careful and using proper tools & grease when you do the barrel swaps, I would think it would be OK. My big concerns would be minimizing strain on the upper and avoiding cross-threading a barrel nut.
Take this with a grain of salt though, I’m not an armorer.
If you grease the threads properly, It’d be really hard to wear the threads out.
If you are using a GI barrel nut, it is absolutely possible to wear out the threads on the upper receiver. Every time you tighten to that next notch for the gas tube to go through, the threads stretch. It never seems to line up within the torque spec windows. Go to the next notch and you are 100+ ft/lbs of torque. So, yes, they will stretch. How much? No idea. But do it too many times and the aluminum will crack. YMMV
With the non-indexing barrel nuts like the KMR uses, it is not an issue.
I’ve reinstalled GI barrel nuts… and if for example, your tube notch is aligned at 45 lbs… if you reinstall the nut you might be at 41 lbs at the same notch. So you could reinstall quite a few times and still be in torque spec without having to go up to the next notch.
Now since he’s trying different barrels, each install will have it’s own unique nut index point. I don’t see it being an issue.
Yes, it’s possible to wear out or otherwise damage the aluminum threads of the upper during a series of barrel changes. They are aluminum threads after all. But it’s by no means a guarantee that they will fail. Take your time, be careful, avoid over torquing and keep the threads and thread lube clean
+1. You can but you don’t have to. Just spend a few more minutes making sure everything is correct before you start and pay attention as you go.
The teeth on GI barrel nuts usually give out first, since the steel is softer and more prone to galling.
Gas tube holes on free float tube nuts will gall, and armorer wrench pins will bend or snap off first I would say.
7075 T6 Type II anodized is some pretty hard material. I personally grease my threads, after cleaning them thoroughly. I’ve heard of people crushing the front of an upper using an end mill and insane amounts of torque, but have never seen it myself.