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6/21/2017 8:25:40 PM
Posted: 3/25/2012 3:08:53 PM EDT
After a ~50 yard zero, the aperture is further right. Yea I know its not too far off but...

Should I re-torque the barrel?

Link Posted: 3/25/2012 4:08:15 PM EDT
[Last Edit: 3/25/2012 4:09:43 PM EDT by RandyStacyE]
Your front sight is probably canted to one side. I have a Rock River that's like that. I don't know if reinstalling your barrel would help at all.

What kind of front sight do you have?
Link Posted: 3/25/2012 4:32:03 PM EDT
That really doesn't look bad at all. I wouldn't mess with it.

Link Posted: 3/25/2012 5:14:30 PM EDT
well within specs.
Link Posted: 3/25/2012 5:16:23 PM EDT
Originally Posted By RandyStacyE:
Your front sight is probably canted to one side. I have a Rock River that's like that. I don't know if reinstalling your barrel would help at all.

What kind of front sight do you have?


It's a colt M4 14.5 barrel, I eyed the front sight but doesn't appear to canted.
Link Posted: 3/25/2012 7:58:20 PM EDT
looks fine you still got some more adjustment. re-torquing the barrel wouldn't do anything but, lapping the upper might.
Link Posted: 3/25/2012 8:40:23 PM EDT
did you use a reciever block when you torqued the barrel nut? If so get or make some barrel blocks and hold the barrel in the vise when you torque the barrel nut......it can make a difference
Link Posted: 3/25/2012 9:01:18 PM EDT
[Last Edit: 3/25/2012 9:03:27 PM EDT by RandyStacyE]
Originally Posted By Mad-Machinist:
did you use a reciever block when you torqued the barrel nut? If so get or make some barrel blocks and hold the barrel in the vise when you torque the barrel nut......it can make a difference


Are you saying to clamp the upper AND the barrel at the same time when torquing the barrel nut? Or do you mean clamp just the barrel?

Neither sounds practical.

I don't see how the instillation of the barrel would have anything to do with it. If the front sight is slightly canted then that would easily cause this. It could be that the front sight was installed flawlessly, but the machining on the barrel was flawed.

Link Posted: 3/26/2012 8:38:30 AM EDT
Originally Posted By RandyStacyE:
Originally Posted By Mad-Machinist:
did you use a reciever block when you torqued the barrel nut? If so get or make some barrel blocks and hold the barrel in the vise when you torque the barrel nut......it can make a difference


Are you saying to clamp the upper AND the barrel at the same time when torquing the barrel nut? Or do you mean clamp just the barrel?
Neither sounds practical.

You use one or the other, never both fixtures at the same time.
Think about the barrel extension pin.
There is not supposed to be very much "play" as it nests into the receiver, but if there is any play at all....
With a clamshell fixture barrel install, the pin is pushed to the port side of the receiver.
With a barrel clamp fixture, the pin is pushed to the starboard side of the receiver.

Seems like the OP's situation is already too much to starboard, though.

I don't see how the instillation of the barrel would have anything to do with it.

That's right, very little unless someone put enough torque on it to damage the pin or slot.
But then the problem would be too much to port, because those guys won't typically be using a barrel clamp

If the front sight is slightly canted then that would easily cause this. It could be that the front sight was installed flawlessly, but the machining on the barrel was flawed.

Could be the FSB is canted or the pin is off or a combination.

I don't think it's severe but if it bothers the OP, talk to the mfr about a fix.

Link Posted: 3/26/2012 9:26:23 AM EDT
[Last Edit: 3/26/2012 9:27:43 AM EDT by durabo]
1 of a few things.

- Out of spec receiver - maybe it isn't square where the barrel extension mates. fix - new receiver or lapping the current one (i would refinish it with something where you remove the anodizing)
- Canted front sight - contact manufacturer or fix it yourself with another FSB (new pinning or clamp on... clamp on preferred)
- Play in the barrel index pin and slot where it mates - shim it to either side as needed or replace upper or barrel with one with better tolerances.
- Incorrectly installed rear sight - try reinstalling it and making sure it is seated properly.
- Tolerances on the rear sight - Try a different rear sight, maybe you just got one that is a tiny bit canted itself (tolerances are in ALL parts)
- The tolerances on the rail where you mount your rear sight could be a factor too.

Remember that tiny tiny tolerances and differences here and there can contribute to things just being a tiny bit askew... could be any one of these things or multiple things all adding up.

Report back with the issue but as others have said, that is well within "spec" and you might have a hard time nailing down the overall cause as it is probably a combination of tolerances here and there.
Link Posted: 3/26/2012 11:05:43 AM EDT
So what's the trick to seeing if the front sight is canted?

I used a receiver block in a vice, with a torque wrench set to 40 ft/lbs. The wrench slipped off the barrel nut at first, I did the torque it and back if off cycle 3 times then a final torque.

This is a colt carry handle, I will swap it with a LMT rear sight then re zero. Rear Sight Check.

I honestly would like to pull the barrel back off, clean it up, check the index pin for any movement. Then re-torque it.

Link Posted: 3/26/2012 12:17:47 PM EDT
[Last Edit: 3/26/2012 12:20:43 PM EDT by durabo]
Originally Posted By JamisonLaviano:
So what's the trick to seeing if the front sight is canted?

I used a receiver block in a vice, with a torque wrench set to 40 ft/lbs. The wrench slipped off the barrel nut at first, I did the torque it and back if off cycle 3 times then a final torque.

This is a colt carry handle, I will swap it with a LMT rear sight then re zero. Rear Sight Check.

I honestly would like to pull the barrel back off, clean it up, check the index pin for any movement. Then re-torque it.



I would put the barrel in a vise, check that it is level horizontally... at that point you can use your level to check the vertical.

But then again you need to check it against the level of your rear sight.

A super easy but not completely precise way is just putting your carry handle back on, lay the whole assembly on a flat level surface and make sure all of the points on the ears of the front and rear sight contact and it isn't sitting wonky. Not precise by any means but it should get you on paper and easily identify a major cant.

Keep in mind that there might be thicker parts of the metal that can throw any measurements and leveling off a bit... In order to REALLY get an accurate level on it you'll have to get fancy with some measurements and such. But odds are if you have to go that far then the offset probably won't be that much anyways.

You might want to check how straight your barrel is too.. this would be connected to the tolerances in your upper.
Link Posted: 3/26/2012 12:52:46 PM EDT
Originally Posted By iNeXile556:
well within specs.


Agreed. I did have a Colt 6520 that maxed out the windage and I noticed the FSB was canted, and obviously so. I sent the barrel to ADCO and then re-drilled and pin the FSB straight and after that windage was zeroed damn near TDC.
Link Posted: 3/26/2012 1:20:48 PM EDT
i know everyone likes to look immediately to the front sight being canted. But shooter technique can also play a factor. someone else may sight your rifle and it be TDC, and someone else may be need it to the left.

It doesnt look far enough that I would think twice about it. In fact, when I had a carry handle rear sight it looked very similar to that.
Link Posted: 3/26/2012 5:33:32 PM EDT
Originally Posted By JamisonLaviano:
So what's the trick to seeing if the front sight is canted?

I used a receiver block in a vice, with a torque wrench set to 40 ft/lbs. The wrench slipped off the barrel nut at first, I did the torque it and back if off cycle 3 times then a final torque.

This is a colt carry handle, I will swap it with a LMT rear sight then re zero. Rear Sight Check.

I honestly would like to pull the barrel back off, clean it up, check the index pin for any movement. Then re-torque it.



You can try that.

Next time use a barrel block
Link Posted: 3/26/2012 6:01:54 PM EDT
what is this barrel block?
Link Posted: 3/26/2012 6:35:41 PM EDT
Originally Posted By JamisonLaviano:
what is this barrel block?

Here is the USGI method showing the barrel block fitted to a vise.



Link Posted: 3/26/2012 7:46:45 PM EDT
GI's.
What do they know?
Link Posted: 3/26/2012 8:26:36 PM EDT
Originally Posted By 458winmag:
GI's.
What do they know?

Apparently not near as much as some of the kitchen table gun plumbers around here.
Just ask 'em.


Link Posted: 3/26/2012 8:45:21 PM EDT
I don't see how using a barrel vice versus a receiver block would make any difference. The barrel nut is still torqued to the same specs, thereby applying the same pressure to the indexing pin.
Link Posted: 3/26/2012 9:06:06 PM EDT
Originally Posted By chewbacca:
I don't see how using a barrel vice versus a receiver block would make any difference. The barrel nut is still torqued to the same specs, thereby applying the same pressure to the indexing pin.

True. In this case, might not matter.

It is however, the simplest and purest way to install (or uninstall) an AR barrel.
The receiver does not have to be clamped or pinned into a fixture.
Also a very good solution for dealing with a billet upper.
Inexpensive too, often around $15 - $18


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