Gunsmithing barrel misalinged with upper AR

[low_tech]

traded for an no name flatop upper with barrel and free float tube. noticed the barrel was not centered in the tube. put on some proven optics, and dammit if it is not hitting a foot left at 100 yards. no more windage adjustment in the scope.

Is my best bet to assume the barrel threads are off, and thread another barrel on it, or is the problem in the upper?

never did any assembly on AR's before, but one of my brother's is a PD armorer, and he can point me in the right direction.

 

[paraman1]

Re: barrel misalinged with upper AR

AR15 barrels are not threaded into the reciever , they slide into it and are held in place with a barrel nut .

 

[low_tech]

Re: barrel misalinged with upper AR

I will find a drawing...

thanks for the info.

Problem in the upper or the barrel, or the nut?

what do you think?

 

[paraman1]

Re: barrel misalinged with upper AR

It could be any of the above . I would disassemble it , clean everything up , check barrel for straightness and reassemble it . I can't remember the torque setting on the barrel nut but a little google-fu should net you a number that will work . Not all armorers wrenches will allow you to use a torque wrench so if your going to purchase one make sure it has the square hole for attaching a torque wrench . I had a similar issue some years ago but The fix is eluding my memory .

 

[JelloStorm]

Re: barrel misalinged with upper AR

Found on Barfcom:

Barrel Nut - 30 Ft. lbs. Minimum, not to exceed 80 Ft. Lbs. to align the next slot in the barrel nut.

 

[Travis S]

Re: barrel misalinged with upper AR

Tear it down first for sure. Something is amiss that needs to be inspected to find out. Should jump out at you.

 

[hdbiker1]

Re: barrel misalinged with upper AR

Tear it down and check the face of the upper receiver for square to the carrier bore. The barrel extension should also have at least 75-80% contact on the receiver face.

 

[Mcoop8]

Re: barrel misalinged with upper AR

I bet you will learn a lot just by pulling off the the hand guard. most standard contours on AR style rifles result in parallel or non tapered surfaces through out. you can use a few straight edges to evaluate alignment of all the above mentioned potential problems. Lets hope you just find a burr on the face of the upper that can be removed for alignment. Are there any marking on the barrel that might give and idea as to who made it? Do you know if it is a factory build or was it put together by the guy you got it from. I ask because the only time I have seen this was when the assembly was done w/ improper torque.

 

[biner626]

Re: barrel misalinged with upper AR

PT&G used to have these for the purpose of truing the upper receiver face. Honestly as outta whack as yours is I doubt it would help.

 

[Beef_Supreme]

Re: barrel misalinged with upper AR

If it is exaggerated, it could be some numb nut did not get the barrel index pin in the index pin slot in the upper.
Disassembling it is going to be the only option for seeing what exactly is going on.
35-80 ft lbs on the torque, the barrel could also be OVER torqued, in the scenario the low spots find the low spots, vice versa and will give you the exact problem you are describing.
Does it group well just in the wrong place?
Does it cycle and function properly?
Looking at the gas tube in the upper can tell you a lot too.