Canted Front Sight on AR upper

Melnic · Feb 27, 2015

I have a used Surplus Upper. I have to adjust the rear sight all the way left and its still about 4" right @ 50 yards. I noticed the Front sight assembly is canted to the left. The left front sight guard (sides that stick up left and right of sight post to protect it) is dented so I know this thing was dropped at some point. Can a front sight be canted and the issue be the front sight itself and how its on the barrel, or would it be the barrel mounted into the upper?
Can I just remove the pins for the front sight and reinsert after straitening it?

OK, I have to ask the simple question: Is it a bad idea to clamp the barrel in a block of wood (cut with a channel to hold the barrel) and vise and wack the front sight back into position?

BUFF7MM · Feb 27, 2015

Melnic said:
I have a used Surplus Upper. I have to adjust the rear sight all the way left and its still about 4" right @ 50 yards. I noticed the Front sight assembly is canted to the left. The left front sight guard (sides that stick up left and right of sight post to protect it) is dented so I know this thing was dropped at some point. Can a front sight be canted and the issue be the front sight itself and how its on the barrel, or would it be the barrel mounted into the upper?
Can I just remove the pins for the front sight and reinsert after straitening it?

OK, I have to ask the simple question: Is it a bad idea to clamp the barrel in a block of wood (cut with a channel to hold the barrel) and vise and wack the front sight back into position?

Find a good smith, it's not worth taking the chance of messing things up.

alucard0822 · Feb 27, 2015

It can happen with cheap builds, or the sight can be bent, either way you basically need to press/hammer out the EXTREMELY tight pins, press the sight off, replace if bent, then press back on straight, drill for the new taper pin position, and press them back in. Will probably bend or damage the sight or barrel if you try to pound it straight. Also need to make sure the gas port in the barrel lines up with the hole in the sight base or else you will have a single shot. The barrel extension pin locks it to the barrel and locates the extension/barrel in the reciever straight, but it is also possible this was not straight. All together the barrel, barrel extension/pin, gas port, sight base and flash hider need to be lined up straight for the barrel to be indexed right. A gunsmith will probably charge more than a new barrel to fix the one you have, and that is if he can save it to begin with.

lsw · Feb 27, 2015

Melnic said:
I have a used Surplus Upper. I have to adjust the rear sight all the way left and its still about 4" right @ 50 yards. I noticed the Front sight assembly is canted to the left. The left front sight guard (sides that stick up left and right of sight post to protect it) is dented so I know this thing was dropped at some point. Can a front sight be canted and the issue be the front sight itself and how its on the barrel, or would it be the barrel mounted into the upper?
Can I just remove the pins for the front sight and reinsert after straitening it?

OK, I have to ask the simple question: Is it a bad idea to clamp the barrel in a block of wood (cut with a channel to hold the barrel) and vise and wack the front sight back into position?

That's what I did with my vz2008, but I have no idea how tight a fit the sight-to-barrel is on an AR, or how tight a fit the taper pin is in comparison to a vz.

I believe you could drive out the taper pin, shift the sight, then redrill for an oversized pin, but there are many more knowledgeable than me on this board who can give you a more definitive answer.

Melnic · Feb 27, 2015

Hmm, sounds like the simple and cheap solution if I want to shoot this thing and hit what I'm aiming at may be to just get a tall thin front sight post insert thingie, then bend it to the right. Its only about 1mm off at this point.
Although used, I'm not interested in changing much to it or messing it up.
I'm also not interested (yet) in sending it to a gunsmith either. It did not cost me that much.

clandestine · Feb 27, 2015

Torque on the barrel nut will clock a FSB to the left if the index pin is slightly undersized or soft. It's a common problem that plagues many ar manufacturerz. Windham weapons had a custom fixture created to prevent clocking from barrel nut torque.

The upper index cut could have been peened or cracked as well.

Find an AR guy to fix it.

Melnic · Feb 27, 2015

clandestine said:
Torque on the barrel nut will clock a FSB to the left if the index pin is slightly undersized or soft. It's a common problem that plagues many ar manufacturerz. Windham weapons had a custom fixture created to prevent clocking from barrel nut torque.

The upper index cut could have been peened or cracked as well.

Find an AR guy to fix it.

Looking from the rear, the front sight is canted counter clockwise so that matches what you say. Several of the other surplus uppers I looked at had loose barrels.

Melnic · Mar 2, 2015

Ok So I pulled the gas tube out then removed the barrel nut. The barrel has some play in it. I took this pic. When I pulled the nut off it looked like the notch was all the way to the side it was canted towards Can I shim one side to get the front sight aligned and keep it tight when tightening up the barrel nut to the proper torque?

clandestine · Mar 2, 2015

You located the problem. Great job.

From the pictures I couldn't say if the upper receiver or the barrel index pin is the problem.

You could shim the index pin but you should use something very hard. Also use aeroshell 33ms for the barrel nut when you reassemble. You can buy small amounts on ebay.

303_enfield · Mar 2, 2015

Beer can shim, snug the barrel nut three times. Use a barrel vise, not clam shell, to assemble. If the upper is a one time use, bed the barrel/receiver with Loctite. Common problem with a easy fix, most of the time.

Melnic · Mar 2, 2015

I went ahead and shimmed it with some sheet steel I had (0.008").
Used the tools I already have (just got in a wheeler AR tool kit)
The upper was a tad peened. I would have expected the pin on the barrel to be square with some taper to the end or something. Dunno if round is standard or not. Torqued it up and aligned the hole for the tube and put it back together. Noticeably straighter now. If its off, I can't see it easily. I'm sure it will rain when I want to check it out.

I'll have to look into the aeroshell 33ms. I have some different anti seize I thought about using but did not. Was not sure if they were good for the heat. I did take a bronze brush to the threads on both sides to clean them up before re-assembling.

Magnumite · Mar 3, 2015

Feeler gauges of proper thickness cut with snips and deburred work well for these type jobs.

303_enfield · Mar 3, 2015

Did you use Molybdenum-Disulfide grease (per the TM) on the receiver threads? This is found at any auto parts store or hardware store for cheap. At the auto parts store - just buy generic WHEEL BEARING grease without Teflon. If you didn't, take her down, grease and reassemble.

The pin is always round. Now, I have seen a few rolled spring pins used on really old Olympic Arms uppers.

Melnic · Mar 4, 2015

Educate me here. Whats the difference between the aeroshell 33ms or Molybdenum-Disulfide grease
and say some stuff I already have like:
Mobil 1 synthetic grease
CVA Nipple Grease
CVA Anti Sieze
Lube-o-Seal NM91
Safe-T-Eze

clandestine · Mar 4, 2015

You can use other greases but the aeroshell 33ms is what is approved for that application. The grease prevents corrosion that takes place when there are dissimilar metals.

I have also seen non approved greases not allow barrel nuts to line up within the specified torque specs and when switched to 33ms they magically lined up.

Using too much torque on the barrel nut will stress the threads and can cause accuracy issues.

Canted Front Sight on AR upper

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