Bent Barrel

A few years ago during a rifle qualification (failed at first) I discovered my rifle was shooting 14 inches left from the previous 100 yard zero. Upon further inspection the barrel nut was loose. I torqued to spec and went to zero the rifle. I am using A2 sights. The rear sight had to be burried to the right to get the weapon zeroed. There is maybe 1/16" of adjustment right left. We don't have a barrel straightness gauge so I gave the rifle to an Air Guard Armorer from work to take and check straightness. He said he dropped the gauge in after cleaning and it was very slow to slide through the barrel. His assessment; it's bent. I spoke with the boss in charge and asked for a new barrel. I didn't get an exact answer but something to the effect of well if it's zeroed it should be good. I've only taken the colt armorer course and Sully's basic course (highly recommended over the Colt course) and don't know what argument I can use to get a new barrel. For those with more experience than me, is this something I should be worried about.
1) he is in an admin position and doesn’t have a rifle issued
2) the response would probably be the same as when I asked for a new barrel

Wondering if there is “science” behind why I NEED a new barrel because XYZ and not just WANT a new one even though it is zeroed now.


Regular Member
What is the barrel profile and brand of the upper/barrel?

I believe the barrel is fine seeing as the gauge did not bind on the barrel. In my experience if a gauge gets hung up then the barrel is bent and trashed, slow to drop out is fine.

My thought is that the front sight base was not pinned in precise manner and thus is the reason for you running out your zero.
Colt HBAR. When I zeroed the first time the rear sight was pretty close to center. After two or three drops out of my locker on the barrel and a few years of bouncing around in the trunk the picture is the result.


Regular Member
It probably has to do with the tightening of the barrel nut. The barrel should be fine from drops and bouncing around, even more so seeing that it is a heavy profile.

I would see if barrel moves rotates side to side while the index pin is still in the notch with the barrel nut loose. Chances are you could've rotated the barrel off to one end while tightening down causing you to compensate by maxing out the windage on the rear sight.
Assuming this is for an LE rifle qual?


You write a memo saying what you discovered and how you did it requesting a new barrel or a new upper.

If they deny it and you end up having to use it on duty and have some sort of issue stem from it (like a round hitting someone who is an unintended victim) the department, namely the supervisor who denied the request is liable.

They have all the legal exposure in this, not you one you document it.
It was actually discovered during a SWAT selection process qualification. I agree with the memo route, was just looking for a specific rational to cite that validates my request to counter the “well the rifle is zeroed now so it should be fine” response.
When the barrel nut was found loose, you say that you torqued the barrel to spec, did you remove the barrel or just tighten it back down? If you just tightened it back down, it may be possible that when it was loose that some carbon type fouling worked its way under the barrel extension / receiver area, and could have changed things just enough that the tolerances shifted. It is possible that when the barrel was loose, that some erosion or abnormal wear occurred during shooting or from road vibration when being carried in a car.

I might suggest pulling the barrel off the receiver, clean things thoroughly, then apply moly paste, retorque and index. If things are still off, it could be that the receiver face isn't square, which can be cleaned up on a lathe or sometimes you can lap the receiver (we teach this in our advanced armorer course). If you can get it zeroed, even though the rear sight windage adjustment is to one side, at least it is zeroed and not off the paper. If you think it's bent, the barrel can be gauged for straightness, which you already mentioned that a National Guard Armorer did for you. If I had this barrel in our shop, or at an advanced armorer course, I would have access to a borescope and camera, along with a straightness gauge, and would be happy to take a close up look at it. If the barrel is truly bent, then it should be taken out of service and replaced.

Greg Sullivan "Sully"
SLR15 Rifles
(763) 712-0123


Network Support I
In order for the barrel nut to be "loose" on an AR-15 (or any variant thereof) the gas tube would have to be removed before any torque could be applied to the barrel, this isn't a completely precise process and few minutes (of angle) might be possible, but never should have happened if the barrel nut was torqued down properly from the beginning. I hope that when you "re-torqued" the barrel nut this procedure was also followed, and the problem was reported to your superiors (it's their rifle after all).

Something is very wrong with this rifle, and you should have requested a new rifle (or upper assembly) the second you found the barrel was "loose", at the very least this is indicative of either a manufacturing defect, or someone getting a little WECSOG at some point before this rifle was issued to you.

To be honest, I do not care about the barrel being "bent", if the gauge drops through, the gauge drops through, that's how the gauge works. However if you have a rifle that's rattling parts lose, and then not holding zero this is a much larger potential issue than a bent barrel.

There is a possibility that when the barrel was found to be loose, the re-torquing process shifted the alignment of the pin in the barrel extension that normally lines up the barrel/extension with the upper receiver, colt could have been feeling fairly sloppy and left a wide gap in the front of the receiver. Normally when assembling the barrel and upper, there's a jig that holds the FSB in alignment with the jig to prevent this shifting as the barrel nut is torqued. This can be fixed, and may be the route chosen, but that the barrel nut came lose scares the hell out of me.