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Posted: 9/21/2004 10:56:36 AM EST
General question for the masses....
Do M4's have a specific front sight housing or front sight post that is engineered for the 14.5" bbl length?

Scott
Link Posted: 9/21/2004 11:00:22 AM EST
Colts FSB for the M4 are taller, Bushmaster and others use a taller front sight and a std height FSB.
Link Posted: 9/21/2004 11:52:00 AM EST
[Last Edit: 9/21/2004 11:57:24 AM EST by 1SGA]
I suspected as much. I have built some M4 uppers for buddies deploying and found that they shot super high. The barrels were turned from 20" Krieger NM barrels - very very accurate M4's - all were/have/will be used with optics - but the sights need to be zero'd as a back up. My first thought was that the barrel itself was the culprit, but a little 'rithmatic showed otherwise.

Does anyone sell M4 specific bases or posts?

Scott

I saw Bushy sells a .040 taller post for A3 Uppers.......?????
Link Posted: 9/21/2004 9:50:56 PM EST
[Last Edit: 9/21/2004 9:52:24 PM EST by eodinert]
I believe 'bravo company' was advertising them here.

'Real' colt M4 FSB's have a very small letter 'F' stamped on the left side, near the base. Presumably this stands for 'flat top'. If you compare one to a non flat top type front sight, you can visually see the difference if they are side by side (the 'deck' where the front sight mounts is higher). Bushmaster will sell you a tall front sight post, but the right way to fix it is with the correct front sight base.

~Doug
Link Posted: 9/22/2004 6:56:56 AM EST
Doug,
Thanks for the info - ordered some through Bravo Co.
Much appreciated.

Scott
Link Posted: 9/22/2004 7:07:31 AM EST
what is the advantage to having a taller FSB, as opposed to the short cut of getting a taller FSP?
Link Posted: 9/22/2004 11:22:15 AM EST
The FSP needs to unscrewed (raised) so high that it actually is even / or above the protective ears of the base. For rifles that are going in harms way - the chance of bending that post are very real. Bear in mind that these are "enhanced" M4's with very accurate bbls. All / most will be used with optics - but those sights are a necessary back up.

Scott
Link Posted: 9/22/2004 11:51:09 AM EST
Bushmaster sells a .040" taller front sight post specifically for M4's that will correct the problems.
Link Posted: 9/22/2004 12:41:24 PM EST

Originally Posted By AR-shoot-r:
Bushmaster sells a .040" taller front sight post specifically for M4's that will correct the problems.



I just ordered one for my latest build. I'll let everyone know how it works out when I get it.
Link Posted: 9/22/2004 9:28:01 PM EST
[Last Edit: 9/22/2004 9:28:58 PM EST by eodinert]

Originally Posted By QuantumPion:
what is the advantage to having a taller FSB, as opposed to the short cut of getting a taller FSP?



It matches up with the taller detachable carry handle. The A2 style sight on the 'A3' carry handle, which moves up and down quite a ways, demands just a little more room than there was space available (at least that's my understanding). The taller front sight post just matches things up.

Yeah, like I mentioned in my first post, you can use the tall sight post... but the right way to fix it is with a new front sight post.. besides, the correct front sight base only costs $15.

~Doug
Link Posted: 9/22/2004 10:44:20 PM EST

Originally Posted By eodinert:

Originally Posted By QuantumPion:
what is the advantage to having a taller FSB, as opposed to the short cut of getting a taller FSP?



It matches up with the taller detachable carry handle. The A2 style sight on the 'A3' carry handle, which moves up and down quite a ways, demands just a little more room than there was space available (at least that's my understanding). The taller front sight post just matches things up.

Yeah, like I mentioned in my first post, you can use the tall sight post... but the right way to fix it is with a new front sight post.. besides, the correct front sight base only costs $15.

~Doug



If putting a new sight base in was as easy as putting a new sight post in, I would do it.
Link Posted: 9/22/2004 10:51:06 PM EST
Colts flat top is extra tall, as per the military spec.
Link Posted: 9/23/2004 5:41:38 AM EST
Is the taller "F" marked FSB that Bravo Company sells of the same quality as the one on my factory Colt Match Target M4? Is it forged? Would that one be the way to go or can anybody suggest a different source? I don't want to sacrifice quality for the glamour of a bayonet lug.
Link Posted: 9/23/2004 6:05:31 AM EST
Okay - I just bought a factory assembled 16" flattop upper from Bushmaster. I didn't opt for a carry handle. I'm thinking about getting one of the ARMS #40 series BUIS. Am I going to run into sighting in problems relating to the front sight post height? I'm confused as hell now. What if I decide to get a Bushmaster detachable carry handle. Will I have problems using the FSP that Bushmaster installed at the factory with the sights in the carry handle? Do I need the higher post or does Bushmaster send these uppers out with the higher one already installed? Can some one shed some light on this for me
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