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Posted: 6/10/2006 8:41:29 PM EDT
Hey everyone.  I have an Arms #40 with a YHM flip-up front sight.  I've got the Arms shifted all the way to the right, but it still shoots 1/4 - 1/2 inch left (at thirty yards).  I cant figure out whats going on, both look mounted centerline.  When the Arms is "middle"  it shoots about 2 feet left at 30 yards.  Has anyone else experienced this?  Or does anyone have any ideas about what's going on?  Thanks in advance.

-RC
Link Posted: 6/11/2006 6:52:30 AM EDT
[#1]
All rear sights are in alignment with the receiver, they have no choice. The problems occure either with the front sights not being in alignment with the barrel, or the barrel not being in alignment with the receiver, or a combo of both.
Brian
Link Posted: 6/11/2006 7:51:30 AM EDT
[#2]
Ok, so, any ideas on how to fix the problem or at least figure out what is going on?
Link Posted: 6/11/2006 1:34:59 PM EDT
[#3]
What is your front sight mounted on?

If the gas block is a bolt on version, it can be loosened and shifted slightly clockwise or counterclockwise (to the left is what YOU need) as needed to correct the mechanical windage offset now present.  Otherwise, reindexing the barrel may be required.

If the front sight is attached to a free floating handguard rail, it might need shifted slightly to achieve what I described with the bolt-on gas blocks.  I'll bet a really "clever fellow" would make up his mind which rail slots the YHM bolts to, and DREMEL away enough material on one side to move the front sight over to one side.  Again, you want to physically move the Front sight to the Left, if your Rear sight is too far Right at present.  HTH.

You can also check to see if the flat-top rail surface and front sight/gas block mounting rail surface are in the same plane by laying sections of cleaning rods across each area, and looking at how they line up when viewed from one end.

Paladin
Link Posted: 6/11/2006 7:29:16 PM EDT
[#4]
ok, thanks.  I dont know about re-indexing, b/c my scope mounts to the receiver, but it has no problems.  I will start with rotating my sight, then look at dremel.  might start with a shim or something first though.  
thanks for the reply.

forgot to add, its an a4 upper, the front sight does screw on.
Link Posted: 6/14/2006 6:39:02 PM EDT
[#5]
Have you tried a different rear sight or a carry handle? It may well be that the ARMS is the problem and not the rail.


All rear sights are in alignment with the receiver, they have no choice. The problems occure either with the front sights not being in alignment with the barrel, or the barrel not being in alignment with the receiver, or a combo of both.
Brian


Suprising a guy that works for arms, with a shrill account, instantly blames the reciever.
Link Posted: 6/14/2006 6:56:49 PM EDT
[#6]
"The front sight does screw on" TO WHAT?  Its a bolt/clamp style to the barrel?  It screws onto your front rail? It screws onto a railed front gas block?

You have not been very clear so we can diagnose the problem.  If its a clamp on (not pinned) front sight you installed it off center, an easy fix.  If its on the frotn rail its probably either your rail or the rails installation.  If its a pinned flip FSB it could be off center.  Or it actually could be the rear sight.  We cant eliminate any of these till you explain how its installed.
Link Posted: 6/14/2006 7:14:54 PM EDT
[#7]
Thanks for the input guys.  Let me try to be more clear...

Heres the upper

Heres the front sight

Arms#40L sp is the rear sight.  the gas block came preinstalled, maybe move it left a little bit?

Again, thanks for the help guys!
Link Posted: 6/14/2006 7:44:26 PM EDT
[#8]
Well I am not real familiar with Armalites railed gas block but either its canted, the front sight is FUBAR or the rear sight is FUBAR.  That is all it can be.  So if you can swap FSB and its the same problem you eliminated the front sight.  If you can swap rear sights you can eliminate the rear sight.  That would leave the gas block.  If I had to guess I would guess its the gas block.
Link Posted: 6/15/2006 2:29:07 AM EDT
[#9]
I just got my 40L yesterday and tried to sight it to where it cowitnessed with my Eotech which was already sighted. I haven't had a chance to site the iron sightss but I had to move it wayyyy right to coincide with the dot and front sight.
Link Posted: 6/15/2006 5:18:58 AM EDT
[#10]

Quoted:
Thanks for the input guys.  Let me try to be more clear...

Heres the upper

Heres the front sight

Arms#40L sp is the rear sight.  the gas block came preinstalled, maybe move it left a little bit?

Again, thanks for the help guys!



FIRST put your rear sight back on mechanical zero/center.  Now loosen the bolts securing the gas block, and rotate it slightly to adjust the windage.  Fire 3 shots, and readjust again.  You want to move the front sight the OPPOSITE direction from where your shots are hitting, I.E. if POI is too far Left, move the front sight to the Right.  Repeat until you are satisfied.

And if you do end up needing a few clicks on the rear that is NOT a big deal.  It helps if you can fine tune it at 50 yards rather than 25 yards.  HTH.

Paladin
Link Posted: 6/15/2006 8:29:22 AM EDT
[#11]
PALADIN-hgwt got the idea.  What I started off with was a red-dot sight (S.P.O.T.) and sighted it in. Then I centered the A.R.M.S. #40L-SP aperature in its housing.  Looking through the rear aperature and placing the red-dot in the center, I could clearly see what adjusting the front sight needed and rotated the gas block and post height until it all lined up.  After that, I took her to the range to confirm adjustments; so far at 50 yds it's perfect.  I was convinced enough that the gas block was where I wanted it, loctited and staked the gas block screws.  
Link Posted: 6/15/2006 2:30:29 PM EDT
[#12]
I figured this was the answer.  Thanks for the help guys!  
Link Posted: 6/15/2006 2:43:48 PM EDT
[#13]

Quoted:
"The front sight does screw on" TO WHAT?  Its a bolt/clamp style to the barrel?  It screws onto your front rail? It screws onto a railed front gas block?

You have not been very clear so we can diagnose the problem.  If its a clamp on (not pinned) front sight you installed it off center, an easy fix.  If its on the frotn rail its probably either your rail or the rails installation.  If its a pinned flip FSB it could be off center.  Or it actually could be the rear sight.  We cant eliminate any of these till you explain how its installed.

what he said Easy fix arm 40 don't have a lot of adjustment like a2 does.
Link Posted: 6/15/2006 3:20:50 PM EDT
[#14]

Quoted:
Have you tried a different rear sight or a carry handle? It may well be that the ARMS is the problem and not the rail.


All rear sights are in alignment with the receiver, they have no choice. The problems occure either with the front sights not being in alignment with the barrel, or the barrel not being in alignment with the receiver, or a combo of both.
Brian


Suprising a guy that works for arms, with a shrill account, instantly blames the reciever.


Especially when you remember that there were several people with the exact same probs with ARMS #40 sights, including some who took pics showing the gaps under the ARMS mating surface.
Link Posted: 6/15/2006 7:38:05 PM EDT
[#15]
I dont get it.  Are you saying it could also be my arms sight?  How can I check this?
Link Posted: 6/16/2006 5:18:42 AM EDT
[#16]
From what I remember there were some people with #40s that were canted on the rail.  If you looked at the mating surfaces with the sight installed, you could see a larger gap on one side of the sight.  IIRC, the sights all had to be adjusted in the same direction, which could have meant that there was a loose run on the #40s.  I wasn't having a prob with my #40, so I didn't keep up with the thread.
Link Posted: 6/16/2006 6:28:17 AM EDT
[#17]
I guess you could center the aperture, fire a string, and then remove the rear sight and install it backwards.  If it now shoots on the other side of the target, the problem is probably the #40.  

If the second string is in the same spot, put the #40 back on correctly.  Fire a string and then put the front sight on backwards.  Fire another string.  If the second string moves to the other side of the target, the problem is with the front sight.

If reversing neither sight moves the zero, the problem is the receiver.

Right?
Link Posted: 6/16/2006 6:24:44 PM EDT
[#18]
or the fsb.  i can give that a try also.  thanks.
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