Zeroing BUIS

Dmn0166 · Dec 3, 2012

I recently installed a Free-floating handguard on my Ar15. While I was zeroing in my back up sights, i noticed my rear Magpul sight Was adjusted almost all the way to the right.

When I went home I tried adjusting the handguard To make sure it was level. Now, after cowitnessing with my red dot sight, my rear buis is 10 clicks to the right. Less then it was, but still alot.

Should I be concerned about this. Or is that amount of adjustment normal.

Thanks,
Derek

Twigg · Dec 3, 2012

Depends on what you mean by "co-witnessing". The handguard is just a handguard and sights don't mount there for a reason. If it's loose it will affect your hold and point of impact.

The BUIS need to be sighted in by themselves with the dot turned off.

The fold down the BUIS and turn on the dot and sight in the dot.

Next unfold the BUIS and look through the optic with the dot turned on.

The dot should be on top of the FSP, or somewhere near it at least.

Just my opinion but with the variety of BUIS components and dot sights out there the possibility of having the dot dead nuto on top of the FSP every time with everydifferent manufacturer's parts could be slim.

I've seen people (who really ought to know better) simple start twisting the knobs on their dot in an attempt to get the dot "co-witnessed" on top of the FSP and then they wonder why they can't hit squat when they try to shoot something.

The position of your rear sight will correspond to where the butt of the stock rests on your shoulder and the place you get your "cheek weld" which is why one needs to do everything the same every time.

Opinions vary, that was mine. Hope you found it helpful.

Billsail · Dec 3, 2012

It happens. The rear BUIS on my MP15 is way over to the right. Could be a number of reasons, from an off kilter front sight, twisted barrel, or bent. As long as I can get a reasonable group, I don't worry. Others that are fussier than me, may not agree. Is it right, no, but it is what it is. I was very disappointed at first, but I didn't have the energy or patience to seek a fix. If someone has a solution, let me know too. Otherwise it doesn't bother me. I always use the red dot, and hit what I'm aiming at...mostly. Good luck.

xtry51 · Dec 3, 2012

Your front sight is not centered properly, requiring the rear to account for the misalignment. If it's shooting good groups and zeroes, whether it is a big deal or not is a personal issue.

Is your Front site mounted to the free float tube, or to the barrel? If it's on the handguard, that's where you're issue is.

Dmn0166 · Dec 4, 2012

My front rail is free float and I had to grind down the gas block in order to install it. I couldnt get a great look at it but it appears the rail may be resting on the gas block. This weekend im going to grind down the gas block more and then check my buis with my red dot thats zeroed.

Twigg · Dec 4, 2012

xtry51 said:
Is your Front site mounted to the free float tube, or to the barrel? If it's on the handguard, that's where you're issue is.

Question seconded. [thinking]

exo · Dec 4, 2012

Derek33 said:
My front rail is free float and I had to grind down the gas block in order to install it. I couldnt get a great look at it but it appears the rail may be resting on the gas block. This weekend im going to grind down the gas block more and then check my buis with my red dot thats zeroed.

Nevermind, misread what you were saying. I would check the alignment of your handguard.

Dmn0166 · Dec 4, 2012

Just an update.

I rechecked my gas block and made sure there was no contact with the handguard.

I've re installed the rail a few times being careful to slowly increase the torque of the four bolts in alternation.

I notice theres a little "flex" in the handguard. If i sit with the rifle between my lap and the barrel facing the ceiling, i can cause the barrel to "flex" to the left when i push on the right rail. But the handguard does not budge if i try pushing it to the right (the direction my sight is adjusted to)

The barrell nut has not been moved since instalation from the factory.

Any ideas?
Thanks

Derek

Dmn0166 · Dec 4, 2012

Additionally. My impression is the handguard is canted to the right but is eventually being blocked by contact with something. Potentially why the handguard can be flexed to the left and not the right.

xtry51 · Dec 4, 2012

You still haven't said whether your FS is on the barrel or on the hand guard.

ThePreBanMan · Dec 4, 2012

On one of my systems I have a troy industries front sight bolted to my Daniel Defense 12" lite hand guard. Have had zero issues and shoot tighter groups with the irons than I do with the aimpoint on. Mounting a sight on a free floating hand guard should not be an issue if assembled properly.

Dmn0166 · Dec 5, 2012

xtry51 said:
You still haven't said whether your FS is on the barrel or on the hand guard.

Its on the handguard. Sorry

Twigg · Dec 5, 2012

Derek33 said:
Its on the handguard. Sorry

Well then, there's your problem.

xtry51 · Dec 5, 2012

Derek33 said:
Its on the handguard. Sorry

The issue is then the hand guard. It's rotated to far and not square to the upper. Keep in mind the Picatinny rails on your hanguard and the ones on your upper most likely will not line up perfectly as they were not machine as a match set. Also make sure that when you adjust it, you loctite the bolts holding it on. I have a BCM upper that came with a DD guard and after about 6 months it loosened up on me and I had the same issue you're having. You can also try adding some Loctite Sleeve Retainer to the mating surfaces of the hand guard and this will help prevent loosening.

Dmn0166 · Dec 5, 2012

Thank you for the advice. I emailed Troy and they promptly replied with the information to send my rail back for them to take a look at.

Dmn0166 · Dec 21, 2012

Troy sent me a new rail. Unfortunately the problem persists of the handguard canting to the right.

What are the next parts besides the handguard that i should be checking for alignment.

Thanks

Derek

Sprocket · Dec 21, 2012

You need a jig to keep the hand guard square to the receiver before you start to torque down things. When you apply pressure, the guard rotates with it.

Otherwise you may be able to trick it into place by starting with the guard slightly canted to the left and torque to the right into place. It's a bugger without the jig...

jar · Dec 21, 2012

Sprocket said:
You need a jig to keep the hand guard square to the receiver before you start to torque down things. When you apply pressure, the guard rotates with it.

Otherwise you may be able to trick it into place by starting with the guard slightly canted to the left and torque to the right into place. It's a bugger without the jig...

A one piece scope mount like a LaRue makes a decent jig for this. Attach it with one of the clamps on the receiver rail and one on the hanguard.

Dmn0166 · Dec 21, 2012

Ill give that a shot when i get home.

Im under the impression the handguard is canted, not rotated. But its worth a shot

exo · Dec 23, 2012

Derek33 said:
Ill give that a shot when i get home.

Im under the impression the handguard is canted, not rotated. But its worth a shot

I highly doubt that Troy made not one but two bad handguards and you got both of them.

Billsail · Dec 23, 2012

Even though it's highly unlikely, don't discount the possibility that it could be the barrel.

ThePreBanMan · Dec 23, 2012

Sprocket said:
You need a jig to keep the hand guard square to the receiver before you start to torque down things. When you apply pressure, the guard rotates with it.

Otherwise you may be able to trick it into place by starting with the guard slightly canted to the left and torque to the right into place. It's a bugger without the jig...

+1

use something like this:
http://yhm.net/index.php?main_page=product_info&cPath=2_4_51&products_id=31

Zeroing BUIS

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