AR15, ran out of windage adjustment???


April 7, 2004, 03:10 PM
I was helping my brother sight in his AR15 over the weekend that he just bought and we ran into a snag.....

With the rear sight adjusted almost all the way to the left the rifle still shoots 3" to the right @ 15yds. I have searched a little here and there and came across two different solutions.

One is to have the rifle sent back to the manufacturer and have the barrel re-indexed.....

Or the caveman approach, pad the rifle and tweak the front sight block with a rubber mallet.....

It's his new toy and he'd hate to have to send it back for any great length of time.

Any suggestions?

If you enjoyed reading about "AR15, ran out of windage adjustment???" here in archive, you'll LOVE our community. Come join today for the full version!
April 7, 2004, 05:00 PM
Howdy Jeff! Thought you'd deserted us.

Sounds like there's an alignment problem between the barrel and upper receiver. Either the barrel is off-center or the barrel is set into the receiver at an angle due to one of the shoulders being out of square. It only takes
about a.005 inch misalignment to throw the shots an inch wide at 100 yards.

re-index the rear sight to the center of its travel and hang a plumb bob
about 50 feet away from the rifle. With the rifle on sandbags, visually cut
the center of the stock with the string and see where the barrel is pointing.

Then reposition the rifle to cut the center of the rear sight mount...the carrying handle, if so equipped and look again. My guess is that you'll notice the barrel sitting at an angle to the upper receiver. Then it's a matter of determining whether the barrel shoulder is out of whack, or the receiver. Either way...without the machine tools and fixtures to true it up, it's back to the manufacturer. If it's the barrel shoulder, a lathe will straighten it out fast and easy...but then there's the matter of the headspace. If it's the barrel extension itself, it will need to be replaced
and headspaced.


One other thought...If he's shooting it with a tight sling on his arm, that will
flex the barrel sideways enough to throw the shots wide of the mark. The
rifle doesn't lend itself well to shooting slings unless beefed up at the junction of barrel and receiver.

Best bet is to bite the bullet and pack it up, along with a polite but unhappy letter.



April 7, 2004, 08:36 PM
It sounds like the barrel need to be re-indexed.
You can do this yourself if you have the tools, but it would probably be easier and cheaper just to send it back.
You don't mention what brand of rifle this is, but this was a problem with Bushmaster at one time.

"Or the caveman approach, pad the rifle and tweak the front sight block with a rubber mallet....."
This is a very bad idea for a couple reasons. The first reason is that it isn't a front sight block, it is called a gas block. This is where gas is bled off from the barrel which then travels through the gas tube located under the handguards eventually ending up at the bolt. This gas block is secured to the barrel by two pins (You can't turn it with a mallet). In addition, this is positioned over a hole in the barrel where the gas is bled off. Move it (which you can't) and you would have made a bolt action rifle out of it. Finally, if you could do this (which you can't) you would bend the gas tube. When you bent it, it would become shorter and not meet up with the bolt.
Another reason this is a bad idea is that you are talking about making a mickey mouse attempt at a repair to an otherwise good rifle just because you want to shoot it RIGHT NOW. Two years from now, the wait will be forgotten. Even if this would work (which it wouldn't), two years from now you would still be looking at a half a$$ed job.

April 8, 2004, 07:01 AM
If it's the gas block, you can't "tweek" it with a mallet. It can be fixed. I've done it 'tween 50 and 100 times but it is not for an amature. First, center the rear sight. Then mount the upper receiver in a mill vice. The barrel is indicated to insure that it is parralel to the table using a device called a wiggler. Then, check to see if the rear sight is centered to the barrel. If it is, then you check the alignment of the front sight. If the front sight is off, it must be remounted. That goes something like this.

The pins must be removed. They're tapered and must be driven out from port to starboard. Using a dead blow composition mallett, drive the front sight off. (note; Any obstruction like flash hiders or compensaters must first be removed.)

Then the hole in the bottom of the rear ring must be taped 6/32 IIRC. Remount the sight/gas block to the barrel and repete the alignment process. when and only when the sights and barrel are aligned, tighten the set screw in the bottom of the rear ring of the gas block. then you can very carefully re-ream the tapered holes for oversized taper pins.

Machinery supply houses like McMaster Carr, Rutland/Air gas, and Granger are good sorces to find oversized taper pin, taper reamers, and the other things needed.

(note; Great care must be taken to assure that the hole in the gas block is aligned to the gas hole in the barrel. A bore scope is a must for this.)

This is not easy and should not be attempted by amatures.

I am not a gunsmith, I'm a machinist, specializing in Tool and Die, Robotics, and Injection Molds. Gunsmithing is just a hobby.:D

April 8, 2004, 10:00 AM
Thanks for all the info guys, I appreciate it.

Tuner, no I haven't abandoned y'all, you just got me all straightened out and ALL my 1911s have become boringly reliable :)

I bought an AK and I'm pretty wrapped up in it right now, alot of fun!

444, I'll heed your warning, I do not want to ruin his rifle, it's an Armalite by the way. "Front sight block" a term I just learned, came with the AK I just bought ;)

4570Rick, sounds like it's outa my league but thanks for the description.

Thanks again,

April 8, 2004, 10:09 AM
Jeff said:

ALL my 1911s have become boringly reliable.

Ah! Excellent news. Much you have learned.


April 8, 2004, 03:46 PM
TuneYoda......I always pictured you taller :D

Lil' brother called Armalite today, they say "It's highly unlikely that the barrel need re-indexed" and they told him to loosen the allen screws to the Gas Block and rotate it a few degrees...... that's what they would do...... :scrutiny:

This is after the gundealer looked at it and said the front sight is just 'canted' .... he suggested the same :confused:

I told him "well go ahead, we'll find out at the range if it works or not"

Does this sound like hot air?

Is there room to rotate the block a few degrees?

April 8, 2004, 03:57 PM
Set screws? Set screws....:scrutiny: Brother, the last M-16s and AR-15s
I messed with (SP-1s) all had a hardened, tapered pin that located the front sight...I guess with all the pseudo 16s and clones poppin' up, anything's possible. I'd never have imagined that anybody woulda
used a cast hammer and sear in a 1911 at one time, but looky where
we're at now...:rolleyes:

So, loosen the screws and see if it works. Nuttin' much ta lose.



April 8, 2004, 04:15 PM
I never had one with set screws either, but if you got 'em give it a try.

April 8, 2004, 04:39 PM
Had the same problem with a NIB AR-180B from Armalite. The rifle would shoot groups 3 feet to the right at 50 feet.

According to Armalite (, Technical Note #53 dated July 26, 2002


Normal manufacturing tolerances can result in the rear sight being off-center when a rifle is zeroed. ArmaLite’s exclusive screw-clamping gas blocks (T and A4 models) and front sight bases (AR-10®, M15-A2™, and AR-180B™) (see figure 1) allow the owner to zero the front sight for windage with the rear sight perfectly centered. This is especially important for competitive shooters, who generally wish to have equal windage adjustments available to both the left and right.

To zero the front sight, put the rear sight aperture in the center of the rear sight base. Fire a three-shot group to see where the rifle is shooting, then adjust the front sight based on the horizontal location of the shot group. To adjust the next shot group to the left, loosen the clamping screws and shift the front sight to the right slightly. Very little movement is needed. To shift the group to the right, move the sight slightly to the left. The sight should be easy to move by hand or with very light taps of a leather or nylon mallet. Tighten the base and try again.

Of course when I tried this, the rifle would be on target, but the gas piston would no longer extract the spent brass, (gas port no longer aligned with barrel).

I ended up shipping my single shot AR back to Armalite with a letter.

There it sits, three weeks later.

Hope you have better luck.


April 8, 2004, 05:04 PM
I dunno guys...Those set screws seem like a chicken$#&t way to make
up for sloppy manufacturing. It's not a big deal to make a fixture to hold the barrel, index the front sight/gas block, and drill and ream one tapered hole.

Then again...bein' a toolmaker has made me a bit anal retentive over

Luck to ya mah fren!

TunerFish YodaBird:D

April 8, 2004, 05:23 PM
pseudo-16 :scrutiny: Boy, ain't it da troot! :rolleyes:

April 8, 2004, 05:33 PM
.:TunerFish YodaBird:D :.

can't stop laughin'..........:evil:

April 8, 2004, 06:02 PM
Hmmmm...Maybe I oughta change that to Yodabird Tunerfish. It does
have a better "ring" to it.:cool:

Much to do I have (sqwawwk!) Dogs to be fed. Nanoo! Nanoo!


Steve Smith
April 8, 2004, 09:09 PM
Tuner, set screws are VERY common in the custom realm of match ARs. We go thought so many barrels they provide the best solution for on-off fitting and a DEAD CENTER mechanical and no-wind shooting zero.

April 9, 2004, 04:41 AM
Sorry 'bout the lack of clearity on my post last night. I read it just now and not to post when I'm that sleepy.:D

The set screw will not hold the gas block on for shootin.:eek:

It is only to hold the block in place while you carefuly re-ream the holes for the oversized taper pins. Once the new taper pins are installed, throw the set screw away.

As far as tapping the hardened gas block...thats why God created TiCN coated carbide tooling.

Above all, the gas port in the barrel must line up with the gas hole in the block or you will most certainly create a single shot AR.

April 11, 2004, 02:12 PM
Well it worked, marked the 'gas block' and barrel with a pencil, rotated the block just slightly and sighted 'er in. Still had the rear slightly to the left but it fed every round properly. Need to get the tool for elevation, it shoots 2" low at 25yds.....wonder where that'll put it at 100yds?

I watched as my brother shot and the empties ejected strait out to starboard, not forward. I have previously seen ARs at the range that eject the brass forward. Do I assume everything is good in this ones gas port alignment?

April 11, 2004, 04:24 PM
Please let us know if you end up having any problems as a result of this. Hopefully, it will continue to run fine.
As I mentioned, this was all news to me about the set screws. I thought I knew something about AR15s (I own 13 of them, manufacturerd by four different companies) but as they say, you learn somethiing new every day.

Obviously you can zero any way you want depending on what you are doing with the rifle. One of the favored methods of zero for a defenisve rifle is the Improved Battlesight Zero. To me, it makes most effective use of the cartridge's trajectory. Using this zero, you would be shooting low at 25 yards. Read about zeroing the AR15 here:

April 11, 2004, 04:26 PM
Howdy Jeff,

Actually, with a standard AR-15/M-16 sighting system, approximately an
inch and a half low at 25 yards would have you very close at 250...It's known as a Battlesight Zero. Two inches low would probably get you very close at 200 yards. It won't be precise, but it will get you on paper.
I'll venture a WAG and say that with the present zero, you'd be about
3 inches high at a hundred.

To adjust the front sight elevation, you can use the tip of a bullet to depress the plunger. The only sight tool that I have is a 5-point tool
for the older rifles. Yours takes one of the newer 4-point tools. If
You can probably find one in Brownells.



April 11, 2004, 06:57 PM
Thanks fellas for the info, I'll pass that on to my brother, if it were mine, I'd leave it there then.....

Happy Easter

If you enjoyed reading about "AR15, ran out of windage adjustment???" here in archive, you'll LOVE our community. Come join today for the full version!