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Posted: 12/31/2005 11:24:31 AM EDT
I have a new A2 20" upper and took it to the range today to get it sighted in. I had to use ALL of the left windage to center the shot group. Once there, I was able to adjust the vertical and start making nice groups. However, I should not have had to use up all the left windage to center the shot. So - is there something I can adjust myself or should I just call the manufacturer and make arrangements to have them fix it?
Link Posted: 12/31/2005 12:11:05 PM EDT
I just had the same thing happen, almost... I'm most all of the way to the left, but careful, careful shooting proved I didn't need to be nearly as far as I thought I did--I'm probably 2/3-3/4 of the travel, though. It's still annoying that I'm as far as I am from dead-center.

I'd say have someone else shoot it, just to confirm your eye, and then yes, if you're not the type to take your barrel off and put it back on or it's a big-name factory-built upper, let them deal with it.

Mine's a Model 1 Sales upper 16" lightweight with an A2 rear sight... I noticed, too, that my rear sight basket is twisted , being held under spring pressure to rotate counter clockwise (when looking down at it)... I'll have to post a pic.
Link Posted: 12/31/2005 12:48:15 PM EDT
[Last Edit: 12/31/2005 12:50:23 PM EDT by cwickgo9]
This is sounding familiar. Mine's a Model 1 20" and the basket does look like it's twisted and under spring pressure. When I twist on it, it moves CCW and then snaps back when I let go.

I have an 80's model Colt that has the fixed rear sight and it is almost dead center of the handle.

Since they're in Whiteright - about an hour and a half away, I may just try to send it back to them. I'll call them next week for sure.
Link Posted: 12/31/2005 6:01:46 PM EDT
[Last Edit: 12/31/2005 6:04:20 PM EDT by VAPORTRAIL]
You guys have a classic case of mis-indexing of the barrel. What that means is when the barrel nut was screwed onto the upper receiver, the barrel rotated slightly as the nut was tightened. The front sight was basically moved to the left.
When you adjust the front sight, you move it in the opposite direction you want the bullet to go. When the front sight was moved to the left, as the barrel nut was tightened, it created excessive right windage. In order to get the rifle sighted in, you needed to move the rear sight left.
If you have a barrel nut wrench, and an action block, you can fix the problem quite easily. If you don't have the tools, get a hold of the manufacturer, and see if they will fix it.
I believe the twisting movement of the rear sight is normal. I like the A-1 sight, because of its simpler, no bling operation.
Link Posted: 12/31/2005 6:44:43 PM EDT
Link Posted: 1/1/2006 5:56:06 AM EDT
[Last Edit: 1/1/2006 6:04:02 AM EDT by cwickgo9]
No - this was the new build I was having mag trouble with. However, that seems to be breaking in okay the more I shoot.

the barrel nut was screwed onto the upper receiver, the barrel rotated slightly as the nut was tightened. The front sight was basically moved to the left.
When you adjust the front sight, you move it in the opposite direction you want the bullet to go. When the front sight was moved to the left, as the barrel nut was tightened, it created excessive right windage.


Is there any way I can verify the barrel indexing? No I don't have a barrel nut wrench or anything else like that (SOME people ignored my Christmas list). But if I can pull the handguards off is there some indicator that I can give the manufacturer so they can verify this barrel rotation?
Link Posted: 1/1/2006 11:47:45 AM EDT
You might be able to see the front sight leaning slightly to the left, just by looking down the rifle. It doesn't take much to throw the sight off.
If you don't have the tools, just give the manufacturer a call.
Link Posted: 1/1/2006 12:10:58 PM EDT
[Last Edit: 1/1/2006 12:11:32 PM EDT by slimslade]

Originally Posted By VAPORTRAIL:
You guys have a classic case of mis-indexing of the barrel. What that means is when the barrel nut was screwed onto the upper receiver, the barrel rotated slightly as the nut was tightened. The front sight was basically moved to the left.
When you adjust the front sight, you move it in the opposite direction you want the bullet to go. When the front sight was moved to the left, as the barrel nut was tightened, it created excessive right windage. In order to get the rifle sighted in, you needed to move the rear sight left.
If you have a barrel nut wrench, and an action block, you can fix the problem quite easily. If you don't have the tools, get a hold of the manufacturer, and see if they will fix it.
I believe the twisting movement of the rear sight is normal. I like the A-1 sight, because of its simpler, no bling operation.



I'm having the same issues with a Bushmaster I rebarreled. I have a action block and barrel nut wrench. What's the easy fix? Back off the barrel nut a hair?
Link Posted: 1/1/2006 12:34:17 PM EDT
Yes, loosen the barrel nut. Then put a wooden dowel, or a screwdriver handle through the front sight.
Try to rotate the barrel in the opposite direction, as you retighten the barrel nut. Line up the notch for the gas tube, and you are done.
Link Posted: 1/1/2006 1:31:45 PM EDT

Originally Posted By VAPORTRAIL:
Yes, loosen the barrel nut. Then put a wooden dowel, or a screwdriver handle through the front sight.
Try to rotate the barrel in the opposite direction, as you retighten the barrel nut. Line up the notch for the gas tube, and you are done.



Thanks! I'll give it a try.
Link Posted: 1/1/2006 1:34:53 PM EDT

Originally Posted By cwickgo9:
This is sounding familiar. Mine's a Model 1 20" and the basket does look like it's twisted and under spring pressure. When I twist on it, it moves CCW and then snaps back when I let go.



Believe it or not, this is normal, and is part of the design.

You've got two likely culprits: either the entire barrel is canted in the upper receiver as mentioned above, or the front sight itself is canted. Chances are that the former is the problem.
Link Posted: 1/2/2006 12:35:28 AM EDT
[Last Edit: 1/2/2006 12:36:25 AM EDT by Tweak]
Link Posted: 1/2/2006 5:49:06 AM EDT
I'm going to try what Vaportrail suggested. One thing I don't understand is how you can pull the barrel out of alignment that far while tightening the barrel nut when the alignment pin fits so tight in the cut out in the reciever.
Link Posted: 1/2/2006 5:57:32 AM EDT
Link Posted: 1/2/2006 10:16:31 AM EDT

Originally Posted By Tweak:
it doesn't take much misalinement esp with the short barrels



I've loosened the barrel nut and am in the process of re torquing using a Snap On click type wrench while at the same time using oposite pressure on the front sight but... I've reached 80 ft lbs and still lack about 1/16 or so before everything lines up
Link Posted: 1/2/2006 2:05:44 PM EDT
You need to recoat the threads, the socket face, and the mating surface inside the barrel nut with a fresh coat of Moly lube or you will have the max torque problems.
Link Posted: 1/2/2006 2:06:43 PM EDT
Link Posted: 1/6/2006 11:04:12 AM EDT

Originally Posted By Dano523:
You need to recoat the threads, the socket face, and the mating surface inside the barrel nut with a fresh coat of Moly lube or you will have the max torque problems.



Did the above and got it to line up at 70lbs, checked head space and put everything back together. I'm going to try to get to the range soon and sight it in.
Link Posted: 1/8/2006 7:20:26 PM EDT
[Last Edit: 1/8/2006 7:24:35 PM EDT by RAINBOW6]

Originally Posted By slimslade:

Originally Posted By Dano523:
You need to recoat the threads, the socket face, and the mating surface inside the barrel nut with a fresh coat of Moly lube or you will have the max torque problems.



Did the above and got it to line up at 70lbs, checked head space and put everything back together. I'm going to try to get to the range soon and sight it in.



Great post. Would like to know the results of the range session as im having the same problem with a Bushmaster barrel/upper receiver that i put togethor. Used the minimum of 30ftlbs on the barrel nut with sufficent moly grease. 23 clicks to the left for windage correction to zero.

I believe someone posted that they used two vises , one for the barrel and one for the receiver to prevent the barrel from twisting over. Sounds like two vises for future assemblies.

Can the index pin become bent as a result of the barrel twisting during the installation?
Link Posted: 1/8/2006 8:31:47 PM EDT
I suppose that the pin could get bent, but I would think that the slot in the upper would be damaged first.
Link Posted: 1/9/2006 2:06:08 AM EDT
Link Posted: 1/9/2006 7:35:56 AM EDT
Took her to the range yesterday. Same 50 meter distance, same ammo, same lot (surplus 55gr. S.A.) same results. THEN taking a closer look at the front site housing by sighting down the flat ribbed part of the A2 handguard it looks like the site housing is canted about 1/8" to the left. Bad alignment job by Bushmaster.

Anyway, I was able to get decent groups at 50 meters with the rear site cranked way to the left If I can get decent results at 100 meters I'll probably leave it as is.

As an interesting side note I also put 30 rounds of S&B 62grn. green tip through the gun at the same target that had been loaded in a Thermold magazine for about a year. These rounds printed about 4 inches higher and about 4 inches further to the left than the 55grn S.A. Looks like if I ran only 62grn. through the rifle the rear sight could be moved more to the center.
Link Posted: 1/9/2006 9:07:56 PM EDT

Originally Posted By Tweak:

Originally Posted By RAINBOW6:
Used the minimum of 30ftlbs on the barrel nut with sufficent moly grease. 23 clicks to the left for windage correction to zero.



the amount of torque has nothing to do with the barrel alinement. you can boresight will installing the barrel or correct the alinement on the range with a no mar mallet but lucking into a acceptable alinement is rare except with the best parts.



Yeah i just added the torque value in as a detail to my assembly procedure. My main point was the use of moly grease to help prevent the barrel/barrel extension from winding up.

Persuading the FSB/barrel with a mallet
Ive bore sighted scoped bolt rifles,but never a rifle with iron sights. Im guessing the proceedure is similar with iron sights.
Link Posted: 1/9/2006 9:25:38 PM EDT

Originally Posted By slimslade:
Took her to the range yesterday. Same 50 meter distance, same ammo, same lot (surplus 55gr. S.A.) same results. THEN taking a closer look at the front site housing by sighting down the flat ribbed part of the A2 handguard it looks like the site housing is canted about 1/8" to the left. Bad alignment job by Bushmaster.

Anyway, I was able to get decent groups at 50 meters with the rear site cranked way to the left If I can get decent results at 100 meters I'll probably leave it as is.

As an interesting side note I also put 30 rounds of S&B 62grn. green tip through the gun at the same target that had been loaded in a Thermold magazine for about a year. These rounds printed about 4 inches higher and about 4 inches further to the left than the 55grn S.A. Looks like if I ran only 62grn. through the rifle the rear sight could be moved more to the center.



Sounds the same as my problem. My barrel assembly and upper assembly are both Bushmaster, but they were purchased seperately then assembled by myself. I suspect a torqued over barrel in my case. Ive had the weapon to the range after the initial assembly and then after a re-assembly. The post re-assembly range session yielded the same results as the first range session. Too much left windage input on the rear sight.
Link Posted: 1/9/2006 10:03:40 PM EDT
Has anyone used this Front Sight Alignment Tool?

$70.00 for a steel rod sounds excessive to a imitation armorer like me but hey if it solves a problem.

I remember a photo in "The Black Rifle" at the Armalite factory showing a guy using a tool similar to this.

Link Posted: 1/11/2006 8:32:51 AM EDT

Originally Posted By HRSGRUNNER:
Has anyone used this Front Sight Alignment Tool?

$70.00 for a steel rod sounds excessive to a imitation armorer like me but hey if it solves a problem.

I remember a photo in "The Black Rifle" at the Armalite factory showing a guy using a tool similar to this.




Which volume of "The Black Rifle" ? I have a copy of the first volume, paged through it twice and did not see the photo your refering to.
Link Posted: 1/11/2006 9:40:41 AM EDT
I'm an idiot and I was tired when I posted...

It is "The book of the AR 15" on news stands now, for about $9 bucks or so.

I didn't buy it but spent an hour reading it while the ol lady bought groceries. and their is a picture tour of the Armalite factory.

A buttload of the dealers in the EE have ads in it as well.

Sorry about the confusion.
Link Posted: 1/16/2006 7:33:58 AM EDT

Originally Posted By Tweak:
usually just a poorly installed barrel. bent barrels and misalined FSBs usually show up as VERY excessive windage, a foot or more off at 25 yards.

take your rifle and a no mar mallet to the range and sight it in using the mallet to adjust the orientation of the FSB, you'll just rotate the barrel inside the upper when you hit the FSB correctly.

read Krazny's tacked thread for more info.



I gave it a couple quick whacks and it seems to have worked somewhat. I'll have to take it back to the range, but I think it will work out.

Thanks for all the help!
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