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12/6/2019 7:27:02 PM
Posted: 2/25/2007 4:42:04 PM EST
I picked up a upper in a trade a while back and finally tried to sight it in tonight. I had to crank the sight almost all the way to the left to get it to hit where I wanted it to. All of the components in the upper are new. CMT receiver, LMT BCG, PRI hand guards, standard front sight, 1/7 twist 16" barrel (not real sure of the make). Any ideas what could cause this? Who can I send this off to to make it right?

Thanks
Link Posted: 2/25/2007 4:43:20 PM EST
Sorry, this should have been put in Troubleshooting. Can someone move me?
Link Posted: 2/25/2007 4:47:07 PM EST
[Last Edit: 2/25/2007 4:48:31 PM EST by ALPHAGHOST]
could be several problems:

1st, what kinda ammo? (probably not the problem, but it would be good to know anyways...)

2nd: what kinda rear sights? A2? BUIS?

more likely problems:

--canted FSB--leads to the front sight being canted
--bent bbl--bullets going off a straight line
--upper reciever notch for the bbl is widened too much and your bbl is not locked in--bbl can be installed swayed
--bbl nut is loose--bbl is moving

there are other possible problems, but i'll have to think on em...

you can either try to figure out the problem yourself or send it off to one of the guys in the EE/Ind forum (maybe ar15barrels (mr randall) or ADCO can help you out...)
Link Posted: 2/25/2007 4:49:24 PM EST
The pin that aligns the barrel is bent. I saw this in the Bushmaster web site. easy fix.

Link Posted: 2/25/2007 4:51:00 PM EST

Originally Posted By ALPHAGHOST:
could be several problems:

1st, what kinda ammo? (probably not the problem, but it would be good to know anyways...)

2nd: what kinda rear sights? A2? BUIS?

more likely problems:

--canted FSB--leads to the front sight being canted
--bent bbl--bullets going off a straight line
--upper reciever notch for the bbl is widened too much and your bbl is not locked in--bbl can be installed swayed
--bbl nut is loose--bbl is moving

there are other possible problems, but i'll have to think on em...

you can either try to figure out the problem yourself or send it off to one of the guys in the EE/Ind forum (maybe ar15barrels (mr randall) or ADCO can help you out...)


-Ammo was Guat
-Rear sight is Larue BUIS
Link Posted: 2/25/2007 4:51:07 PM EST
Link Posted: 2/25/2007 5:00:10 PM EST

Originally Posted By bmyk:
The pin that aligns the barrel is bent. I saw this in the Bushmaster web site. easy fix.



Easy if you have the tools
Link Posted: 2/25/2007 5:08:27 PM EST
yo, ThePrepared_com, out of curiosity: why do you say "Rear sight is Larue BUIS"?????
Link Posted: 2/25/2007 5:10:00 PM EST

Originally Posted By BeantownBrawler:
yo, ThePrepared_com, out of curiosity: why do you say "Rear sight is Larue BUIS"?????


?? Because thats what I have and someone asked what I had. I dont think it has anything to do with the rear sight but you never know.
Link Posted: 2/25/2007 5:14:35 PM EST
sorry, I didn't realize you were the originator of the thread. i thought someone was pointing a finger at the LaRue BUIS without knowing what type of BUIS you had. Again, sorry!!!!
Link Posted: 2/25/2007 5:19:46 PM EST

Originally Posted By BeantownBrawler:
sorry, I didn't realize you were the originator of the thread. i thought someone was pointing a finger at the LaRue BUIS without knowing what type of BUIS you had. Again, sorry!!!!


No problem, I was a little confused by your question. I have full confidence that the Larue sight is fine.
Link Posted: 2/25/2007 5:20:34 PM EST
[Last Edit: 2/25/2007 5:23:31 PM EST by 45B10]
Id say either the indexing slot in the upper or the barrel index pin is wore or maybe both. What happens is when you are tightening the barrel nut the barrel turns just a tad. Alot of times you can hold the upper in your lap and smack the fsb( towards the ejection port) with a rubber mallet and itll move enough to straiten things out. If this doesnt work you may have to loosen the barrel nut and retighten it while holding the barrel straight. We run into canted FSBs alot when installing new barrels on older receivers.
Link Posted: 2/26/2007 2:37:13 AM EST
Any suggestions on where to send the upper to get it fixed?
Link Posted: 2/26/2007 9:45:41 AM EST
Bump
Link Posted: 2/26/2007 1:39:11 PM EST
No suggestions on where to send it to have it fixed?
Link Posted: 2/26/2007 1:47:30 PM EST
ar15barrels.com - seems to be an emerging "go to" guy for the boards members

MSTN - (maybe he could/would help. I would call him first)

Bushmaster- They are used to fixing this problem (link - click here)

Link Posted: 2/26/2007 5:20:20 PM EST

Originally Posted By BucsFan1:
ar15barrels.com - seems to be an emerging "go to" guy for the boards members

MSTN - (maybe he could/would help. I would call him first)

Bushmaster- They are used to fixing this problem (link - click here)



Thanks, I will get in touch with them.
Link Posted: 2/26/2007 6:41:05 PM EST
Hrmm, the more I look at the FSB the more it looks like its canted off to the left.
Link Posted: 2/26/2007 8:14:16 PM EST
I will bet it is the FSB.
Link Posted: 2/27/2007 4:41:53 AM EST

Originally Posted By chewbacca:
I will bet it is the FSB.


Some are saying that I can just knock in back into place with a rubber mallet. But how do you get it perfectly straight that way? Also, if I were to do that would it stay where its supposed to?

Link Posted: 2/27/2007 4:50:32 AM EST

Originally Posted By chewbacca:
I will bet it is the FSB.


Yeah, I'd start there. I would imagine canted FSBs is more likely than a bent index pin.
Link Posted: 2/27/2007 5:08:45 AM EST
How exactly does one un-cant a canted FSB if it's pinned on? Set screws I can see, but taper pins?
Link Posted: 2/27/2007 5:18:18 AM EST
[Last Edit: 2/27/2007 5:19:44 AM EST by KnobCreek]

Originally Posted By CasualObserver:
How exactly does one un-cant a canted FSB if it's pinned on? Set screws I can see, but taper pins?


Assuming the gas port is also misaligned, relative to the index pin, I'd say the only way to correct the problem would be a rail mounted flip-up sight (remove the FSB, install a gas block).

I'm not sure how much "play" you have with a clamp on device if the gas port is "off-center".
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