Is my barrel off or is it the receiver?

[UTShooter71]

Hello,
I am working on a new build.! Nothing fancy. Just a standard 16", flat top, 5.56 black rifle. Well I thought I was done but after torquing the barrel but on and slipping on the free float hand guard I noticed the is not centered. I have taken back apart. Made sure alal the surfaces are clean but its off kilter. Is there a quick way to find out if I need a new upper or a new barrel?

Thanks

[markm]

The barrel index pin on the back of the barrel, at the barrel extension should be top dead center. (and aligned with the gas port TDC as well) The upper receiver should have the slot for the index pin at TDC as well. There's not much room for deviation there. What kind of handguard?

[Aetius]

What brand of barrel, upper receiver, and handguard?

[UTShooter71]

Hello,

The upper is Palmetto State, as is the barrel (16" standard), the original free float Mlok handguard was Troy. The new one I picked up to replace (on the cheap) was one by AR15handguard.com(?). I am at a loss.

[bamashooter]

[QUOTE=UTShooter71;2860972]Hello,

The upper is Palmetto State, as is the barrel (16" standard), the original free float Mlok handguard was Troy. The new one I picked up to replace (on the cheap) was one by AR15handguard.com(?). I am at a loss.[/QUOTE]

Considering the replies, where are you at a loss? Determining dead center of barrel to rcvr regardless of how it currently appears, other?

Does the index pin fit snugly or does it have enough slop (doesn't take much) to allow the barrel to cant when tightening the barrel nut? Look at the index pin as top dead center (TDC). The gas port of the barrel (and gas tube, etc) should be in perfect alignment with the pin. The easiest way for this to occur is for a properly manufactured barrel extension and index pin to be correctly installed to the barrel. Additionally, the slot for the pin needs to be correctly machined into the upper rcvr. Correctly machined means alignment and size. Sometimes shim stock is used to fill in the gap (slop) of an other than perfect pin slot on an upper rcvr.

I assume you have M4 ramps. A center line should equally split the ramps (left to right), travel towards the muzzle end bisecting both the index pin and barrel gas port.

There's a few things to check regarding barrel to rcvr alignment. The first thing I'd check is the barrel extension end of the barrel (ramps), everything in between, terminating at muzzle end.

Crap. Reread the op. Thought it was misaligned barrel.

How does this particular handguard attach? Was the Troy straight?

[UTShooter71]

Prior to removing the Troy handguards nothing appeared out of alignment and it zeroed easily. The rear sight wasn't moved all the way to one side to achieve good sight alignment. I am going to re-clean every surface that interfaces with one another and if it is still off I am taking pictures to better illustrate what I am dealing with.

[glocktogo]

Just FYI, I have in the past received an upper from PSA that was out of spec and the barrel wouldn’t index correctly. I called them with specifics and they sent me another one. They didn’t even ask me to send the defective one back. The replacement lined up perfect.

I ended up truing the defective one myself and got it to line up correctly on another budget build.

[Steve-0-]

Prior to removing the Troy handguards nothing appeared out of alignment and it zeroed easily. The rear sight wasn't moved all the way to one side to achieve good sight alignment. I am going to re-clean every surface that interfaces with one another and if it is still off I am taking pictures to better illustrate what I am dealing with.

What distance did you zero at? Also, it should be noted that rails that have very little surface contact with a barrel nut, like the troy alpha for instance can easily be forced to one side. Some rails can even develop an upwards cant if the bottom clamping mechanism is over torqued. i used to see this on Samson Evo rails.

[UTShooter71]

Okay, so just to see if it was the cheap handguard that I picked up I bought a new set. This is a Matrix Arms free-float. When I just set the barrel into the upper it lines up perfectly. When I hand tighten the barrel nut it stays lined up perfectly. After I torque the barrel nut down the barrel still points right, visibly out of center inside the free-float handguard. I don't know what to do. Is it the barrel, where would I look for something to be "off"? Is it the upper? Maybe I just didn't notice it with the Troy handguard.

[TonyAngel]

I've used the handguards from AR15handguard.com for toy builds, like .22s or range only guns. You really need to watch those. They are all made in China, well, the ones I've gotten were, and you have to take care when installing them. Still, all of the ones that I've gotten have installed straight. I use the ones that come with a steel barrel nut and clamp on. When installing the handguard, I use a long picatinny riser that I have to bridge the upper and handguard to make sure everything is straight and then tighten down the handguard to the barrel nut.