How do you adjust an AR15 barrel to realign windage?

[iamkris]

I have an Oly Arms 9mm AR upper that is a lot of fun. Reliable, fairly accurate, cheap to shoot ($2 a box for my reloaded, lead cast 9mm), fun for new shooters and children (low weight, recoil, blast) and old guys (fun to cheaply put multi-9mm slugs in a target) and generally has 32-round blasty goodness.

Problem is, the rear sight is all the way over to the left to bring it to regulation at 25 yards. I've heard that I can take apart and reassemble the barrel to adjust that windage point of zero...I already have a barrel wrench and can pick up a receiver vice pretty cheaply.

Can anyone give me directions/advice on what I will be doing to adjust the windage?

Thanks.

 

[de]

I too had that problem with a bushmaster. I didn't however use a receiver vice as they are easier damaged. Order or borrow a BARREL VICE. Don't cost much. Take the gas tube out and loosen the barrel nut. Turn the barrel (front sight and all), in the appropriate direction very slightly. Tighten the barrel nut, re-install the gas tube and your in business.
NOW, I am not familiar with the nine mill conversion but, am guessing its blow back operated. In that case skip the gas tube step.
Good Luck

 

[boing]

Scroll down to the section "Changing your own AR15 barrel for dummies"

http://www.ar15.com/forums/topic.html?b=3&f=4&t=226782

Note this section:

There is a locator stub on the barrel that fits in a notch in the upper receiver. If there is any play here, line up your front sight so that it is the straightest with the rear sights. Sometimes, it *may* necessary to file this notch open in one direction, if your front sight will not line up straight. I dont recommend cutting anything at first; assemble your barrel, and only perform this procedure if your sights require a lot of windage adjustment in one direction to zero it.

And here:

Q5. "I installed my barrel, but my FSB seems canted in one direction, and in order to zero, I had to move my rear sight all the way to one side, and sometimes it still wont zero because I ran out of windage"

A5. This is a direct quote from Homo_Erectus on the issue:

"This is a very common problem with a very easy fix. It's caused by small differences between the upper receiver notch and barrel pin. And here's how you fix it:

Unscrew the barrel nut. With the barrel in the upper receiver, check the sight alignment by eyeballing it. If it's canted to one side, try and twist the barrel in the upper. If it won't move far enough, then take a jeweler's file and very carefully file the side of the upper receiver notch to open it up until the front sight can sit up straight.

Before reinstalling the barrel nut, you have to tighten up the receiver notch so the barrel won't move around while you're cranking down on the nut. With the barrel in the receiver, take a small hammer and punch and very lightly peen down the loose side of the notch. Careful, tap lightly because it doesn't take much. What you'll see is a slight flattening of the threasd right next to the barrel pin. That's it!

This really easy, and doesn't entail doing anything to the FSB."

 

[Critter183]

Nice thread. I have same problem with an old Colt SP1 receiver with a 16" wilson barrel. I lived with it but it was annoying. I always suspected that turning the barrel was the way to fix it. Now I know for sure.

 

[DougW]

I have changed out 3 barrels on my AR's and there was never enough play in the barrel alignment pin and the notch cut in the upper reciever to make front sight adjustments. All of mine were very tight in fact, with no play at all. I have read that you can dremmel the reciever notch (I would never recomend this), but remember, turning the barrel/front sight could cause the gas tube to start binding, creating another issue of having to bend the gas tube. If your front sight is pinned, then usually only a gun plumber can fix it because the pin holes were miss drilled.

This is why 2 of the 3 barrel jobs on my rifles were completed by replacing the front sight base with a 4 picatinny gas block.

If it were mine, I would leave the barrel attached to the reciever and change out the front sight with one that can be rotated. I have learned to only mess with the cheapest part. There are a lot of nice front sights out there that are held on by set screws that are cheaper than a new upper. That way, you can dial in the sights at the range and know how much "left/right" movement is needed.

 

[iamkris]

Hmm, ok, good advice. I don't like having to file my receiver but that seems the prevalent way to do it.

Speaking of the set screw FSBs...is this what you are talking about? If so, anyone know if there are cheaper alternatives to some of these (best price I've seen is around $40).

 

[DougW]

The pictured FS would be fine. Look up Yankee Hill. They have some nice block/folding FS's. You should get a new gas tube and roll pin.

Keep in mind that you will have to remove the flash hider to get the old FS off. The old front sight could be dremmeled off after removing the pins, but you still have an issue of getting the new one on. Look up in www.Brownells.com under front sights for AR's, and there is someone offering a FS that clam shell clamps to the barrel, so that the flash hider does not have to be removed.

Good luck!

 

[boing]

You may not need to file the receiver. If the slot is just too wide, you may still be able to realign the barrel as needed and torque the nut.* It just might take a little trial and error to get the barrel torqued down in the right place. IMO, even if you have to file (not Dremel ) the slot, it's still the easiest, lowest-impact way to fix your zero. If you over-file the slot, the receiver is still fine, you'll just have to do the trial and error alignment thing anyway.

If your bad zero is the result of a mis-pinned sight tower (and not a mis-aligned barrel assembly/out-of-spec slot/pin), then the gas tube is already out of alignment now. Re-torquing the barrel would correct this problem, bringing the sight tower into proper relationship with the receiver.

This assumes the gas block/sight tower is to spec. Just about all of the out-of-whack windage problems I've heard of come from mis-aligned barrels, not bad gas blocks.

*Editted to add:

I have changed out 3 barrels on my AR's and there was never enough play in the barrel alignment pin and the notch cut in the upper reciever to make front sight adjustments. All of mine were very tight in fact, with no play at all.

I've done two, and they were the same as Doug's. They both dialed right in. I didn't want to give the impression that over-wide receiver slots were common or anything. You may not have to file the slot, but don't be surprised if that turns out to be the case. I still think it's the straightest line between two points.