View Full Version : Problem while zeroing new mid-length carbine
John E. Napalm
07-26-08, 09:28
Hello,
I took my new mid-length carbine to the range yesterday to zero it and see what it could do. I was shooting with the Troy back up rear sight assembly that I purchased with the upper. I initially had trouble hitting paper at 25 yards and finally figured out the gun was shooting low and right. I made the necessary adjustments to get it centered, but I was surprised how much I had to adjust the rear sight to get on target. When I was done the windage adjustment on the Troy was almost all the way to the stop to the left.
This is the first AR I’ve owned without the old standard carry handle rear sight, so I wanted to ask if this is at all common when using a BUIS. I would be a bit concerned if I had to use the much windage correction with one of my standard AR’s. I’m not sure if this indicates there might be something wrong with my upper or not.
The Troy seems to be mounted securely, the upper and lower don’t have any play, the front sight base is tight, so I’m not sure what would cause this unless something is not aligned properly. I’d appreciate some opinions about this problem. I guess I’m curious if something like this merits a call to the customer service people.
Thanks,
J.E.N.
LettersFromEarth
07-26-08, 10:25
J.E.N.
What brand of ammo were you shooting, bro?
Sounds like a standard canted FSB but it could be something else. If canted FSB, corrective action is to remove barrel and reassemble.
Who is the mfg? Have you tried contacting them for a return?
Cowtown556
07-26-08, 11:30
Was it a Sabre?I just got an other Sabre barrel in May,built it up last week,put it on two upper to check, it is 20 clicks left on both. I just wrote to the guys at PK about it this morning.
John E. Napalm
07-26-08, 11:50
While I was on the range I was firing some milsurp 62 grain Canadian ammo and some Spanish 62 grain stuff with a NATO stamp. Both of them have always shot well out of my HBAR.
Both my upper and lower are CMMG. I haven't contacted them because I wanted to hear what the M4 brain trust had to say. I was wondering if they test fire thier uppers before they sell them.
I am a little curious about this. How will removing the barrel and re-assembling fix this? There is an alignment pin on the barrel and the upper receiver has a slot for it to go into. So unless the pin was snapped during installation by an over agressive assembler or the notch in the receiver has been worn out how will this solve the problem?
Sounds like a standard canted FSB but it could be something else. If canted FSB, corrective action is to remove barrel and reassemble.
Who is the mfg? Have you tried contacting them for a return?
Sometimes the slot in the receiver is a bit wide and the barrel rotates during initial assembly as the nut gets torqued down. I suppose pins can get bent, but I'm not sure how prevalent that is.
From what I understand, you disassemble the works and reassemble, making sure the slippage/rotation doesn't happen. I'm not up to all the tricks of the trade, I understand there are shims you can use to preclude this, greasing threads and the face of the barrel collar is another.
I have never seen the pins bend, but I have seen a few actually snap. If the receiver slot is wide, then IMO it is either a crappy upper or has been rebarreled a few times. If it is too wide then it will be very difficult to prevent it from moving. I always use anti-seize on the threads and tighten/ loosen the retaining nut 3 times before final installation.
Never seen or heard of the shims, doesn't mean they aren't out there. The only guns that I have rebarreled were Colts, FN and Bushamsters.
Sometimes the slot in the receiver is a bit wide and the barrel rotates during initial assembly as the nut gets torqued down. I suppose pins can get bent, but I'm not sure how prevalent that is.
From what I understand, you disassemble the works and reassemble, making sure the slippage/rotation doesn't happen. I'm not up to all the tricks of the trade, I understand there are shims you can use to preclude this, greasing threads and the face of the barrel collar is another.
You could slap a scope on it and get it zeroed ,than see where you are with the irons. maybe the BUS is f*cked up or the FSB is canted.
I'm wondering if this is caused by builders who torque the compensator on while holiding in the upper in a vise block. It seems adjusting the windage all the way to the left is the most common complaint, which is what you would expect from an overtorqued barrel.
Soulrack223
07-26-08, 18:21
Usually if the barrel rotates when it's being torqued, it will cause the rear sight adjustment to move it to the right, not the left. In other words, if there's play in the barrel indexing pin in the upper, it would naturally move with the barrel nut as you tighten it. Thus canting the FSB to the left and requiring the rear sight to be adjusted to the right, not the left.
I would disassemble the upper and see if there's play in the upper reciever when mated to the indexing pin of the barrel extension. If there is play, you will need to keep the front sight to the side of your rear sight adjustment as you tighten down the barrel again. You'll need a second pair of hands to do this, as well as a torque wrench. I just assembled a CMMG upper with a CMMG barrel this week and there was absolutey no play at all between the indexing pin and the upper receiver.
I would also find it very hard to believe that CMMG would have gotten the alignment of the barrel extension and the FSB off. If they did though, I am sure they will make it right. Send them an e-mail and see what they say. My experiences with CMMG have always been positive.
I also just bought a CMMG middy upper, however I had to adjust my Larue BUIS way to the right. Also, I had to raise the front sight post nearly to the top of the FSB wings.
So, I am reading threads like these as I have time to best compose my letter to the vendor.
The FSB is most likely canted.
C4
I comprehend how canting would not only create windage shift, but also it would require the post to be elevated more. I ASSumed if it were canted, it would be readily noticeable to the naked eye...not so, right?!
Wish I had cancelled that 3 month CMMG wait when Noveske Lt Recce became available!
I comprehend how canting would not only create windage shift, but also it would require the post to be elevated more. I ASSumed if it were canted, it would be readily noticeable to the naked eye...not so, right?!
Wish I had cancelled that 3 month CMMG wait when Noveske Lt Recce became available!
The FSB is often times an optic illusion. To some, they look like they are perfect (while they are off) and to others they look canted (while they are straight).
C4
Take it or send it back from whence it came and explain that it is sub-standard and you would like a refund. Then do the right thing and get a B Comp. or Noveske upper.
I comprehend how canting would not only create windage shift, but also it would require the post to be elevated more. I ASSumed if it were canted, it would be readily noticeable to the naked eye...not so, right?!
Wish I had cancelled that 3 month CMMG wait when Noveske Lt Recce became available!
I requested the refund option, but this vendor says if he can't fix it by replacing the FSB, he sends me a new upper ASAP, then hashes it out with CMMG.
What leaves me wondering is, how would replacing the FSB fix the canting? Slightly rotating a FSB could bring the sights into alignment, but then wouldn't the gas tube be slightly out of true (and handguards)?
I have never seen the pins bend, but I have seen a few actually snap. If the receiver slot is wide, then IMO it is either a crappy upper or has been rebarreled a few times. If it is too wide then it will be very difficult to prevent it from moving. I always use anti-seize on the threads and tighten/ loosen the retaining nut 3 times before final installation.
Never seen or heard of the shims, doesn't mean they aren't out there. The only guns that I have rebarreled were Colts, FN and Bushamsters.
I've seen one bent into a sort of right-angle triple zig-zag.
John E. Napalm
08-20-08, 13:40
Hello,
Just a follow up on my initial problem; I sent CMMG an e-mail and explained my problem while zeroing my new rifle. They e-mailed me a UPS label and I sent the upper back to them. About ten days later my upper arrived back from them, pretty darned quick.
I got to the range yesterday and zeroed again. It only took a few clicks on the Troy to get it centered. I’m very happy and have a high opinion of CMMG’s customer service.
J.E.N.
The FSB is often times an optic illusion. To some, they look like they are perfect (while they are off) and to others they look canted (while they are straight).
C4
Is there away to check for this without taking it to the range? Possibly a simple trick?
Is there away to check for this without taking it to the range? Possibly a simple trick?
Yes. You can put a laser bore sighter in and a BUIS and get a good idea how far off it is.
C4
Yes. You can put a laser bore sighter in and a BUIS and get a good idea how far off it is.
C4
Simple enough. Thanks for the suggestion!
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