AR-15 sight mistake (build)

iraiam · August 9, 2013, 07:39 PM

I built a match capable AR-15 out of an old, like new, early 90's Colt Match HBAR.

I made a mistake somewhere though, I had to screw the front sight post down into the gas block quite a ways to battle zero the irons.

So far the FSB, front sight post, and carry handle, all measure the same as my other rifles which are supposedly "milspec", this leads me to believe that my upper receiver is not of the same specification.

here's a list of some of the particular parts I used:

PSA flat top upper, I can't seem to find another one, this was purchased quite a while before I did the actual project. I got it because it was a flat top but did not have the M4 feed ramps, so I could use my old barrel. Casting marks are F with a plain square.

BCM F stamped FSB
RRA NM carry handle

Any ideas where I made my mistake? It's not that big of a deal, I am just going to shorten the font sight post or get a shorter one, aside from this small issue, it's definitely a sub-MOA rifle now.

sailskidrive · August 9, 2013, 07:49 PM

At what distance were you zeroing the rifle? 34M? 50 yards?

iraiam · August 9, 2013, 07:58 PM

I did the standard 25 meter battle zero target at 25 meters, with two different carry handles.

I then shot it at 100 and 200 yards without adjusting anything and got the expected results.

sailskidrive · August 9, 2013, 08:10 PM

There are replacement front sights for the non "F" marked FSB that are a different height so they work properly with the standard height carry handle.

I wonder if you have one of those...

iraiam · August 9, 2013, 08:53 PM

I think you got it, according to my measurements, This will fix it. My current sight post is 0.260" tall, it's screwed down far enough that I measured 0.260 -0.056" = 0.204".

the .200" post from midway should be pretty much a drop in fix.

Thanks,

sailskidrive · August 9, 2013, 08:55 PM

Kewl... good luck w/ the build.

Quentin2 · August 10, 2013, 12:06 AM

I think the problem is the RRA carry handle, I believe they are like ArmaLite, Bushmaster, DPMS and others that have short rear sights to go along with their non-F marked FSB. Milspec carry handles like Colt, BCM, PSA and others have taller sights (you can see the difference if you compare the carry handles).

You can fix this for free by reindexing the carry handle about 15 clicks below their setting for 6/3. Google RIBZ or IBZ for more on how to reindex.

Anyway, fixing the rear sight is the way to go, not putting on a short front post (which won't work with a flip up rear BUIS if you go that route later, which many of us do).

August 9, 2013, 07:39 PM	#1
iraiam Senior Member Join Date: September 6, 2012 Location: Lakewood, CO Posts: 1,057	AR-15 sight mistake (build) I built a match capable AR-15 out of an old, like new, early 90's Colt Match HBAR. I made a mistake somewhere though, I had to screw the front sight post down into the gas block quite a ways to battle zero the irons. So far the FSB, front sight post, and carry handle, all measure the same as my other rifles which are supposedly "milspec", this leads me to believe that my upper receiver is not of the same specification. here's a list of some of the particular parts I used: PSA flat top upper, I can't seem to find another one, this was purchased quite a while before I did the actual project. I got it because it was a flat top but did not have the M4 feed ramps, so I could use my old barrel. Casting marks are F with a plain square. BCM F stamped FSB RRA NM carry handle Any ideas where I made my mistake? It's not that big of a deal, I am just going to shorten the font sight post or get a shorter one, aside from this small issue, it's definitely a sub-MOA rifle now. __________________ NRA Lifetime Member Since 1999 "I ask, sir, what is the militia? It is the whole people except for a few public officials." George Mason

August 9, 2013, 07:49 PM	#2
sailskidrive Senior Member Join Date: October 26, 2008 Posts: 726	At what distance were you zeroing the rifle? 34M? 50 yards? __________________ SailSkiDrive Hk USP 45 Expert, USP 40, USP 9, SIG P226, S&W M&P9, Hk 4, Makarov, Desert Eagle 40, Beretta FS92 Centurion, Kimber TLEII 1911A1, Glock 22, SIG P225, 1943 Rem Rand 1911A1, S&W mod 64, Walther PPQ, SIG P229, Browning BDA 45 (SIG P220), Hk45, SIG P230

August 9, 2013, 07:58 PM	#3
iraiam Senior Member Join Date: September 6, 2012 Location: Lakewood, CO Posts: 1,057	I did the standard 25 meter battle zero target at 25 meters, with two different carry handles. I then shot it at 100 and 200 yards without adjusting anything and got the expected results. __________________ NRA Lifetime Member Since 1999 "I ask, sir, what is the militia? It is the whole people except for a few public officials." George Mason

August 9, 2013, 08:10 PM	#4
sailskidrive Senior Member Join Date: October 26, 2008 Posts: 726	There are replacement front sights for the non "F" marked FSB that are a different height so they work properly with the standard height carry handle. I wonder if you have one of those... __________________ SailSkiDrive Hk USP 45 Expert, USP 40, USP 9, SIG P226, S&W M&P9, Hk 4, Makarov, Desert Eagle 40, Beretta FS92 Centurion, Kimber TLEII 1911A1, Glock 22, SIG P225, 1943 Rem Rand 1911A1, S&W mod 64, Walther PPQ, SIG P229, Browning BDA 45 (SIG P220), Hk45, SIG P230

August 9, 2013, 08:53 PM	#5
iraiam Senior Member Join Date: September 6, 2012 Location: Lakewood, CO Posts: 1,057	I think you got it, according to my measurements, This will fix it. My current sight post is 0.260" tall, it's screwed down far enough that I measured 0.260 -0.056" = 0.204". the .200" post from midway should be pretty much a drop in fix. Thanks, __________________ NRA Lifetime Member Since 1999 "I ask, sir, what is the militia? It is the whole people except for a few public officials." George Mason

August 9, 2013, 08:55 PM	#6
sailskidrive Senior Member Join Date: October 26, 2008 Posts: 726	Kewl... good luck w/ the build. __________________ SailSkiDrive Hk USP 45 Expert, USP 40, USP 9, SIG P226, S&W M&P9, Hk 4, Makarov, Desert Eagle 40, Beretta FS92 Centurion, Kimber TLEII 1911A1, Glock 22, SIG P225, 1943 Rem Rand 1911A1, S&W mod 64, Walther PPQ, SIG P229, Browning BDA 45 (SIG P220), Hk45, SIG P230

August 10, 2013, 12:06 AM	#7
Quentin2 Senior Member Join Date: June 18, 2009 Location: NorthWest USA Posts: 1,996	I think the problem is the RRA carry handle, I believe they are like ArmaLite, Bushmaster, DPMS and others that have short rear sights to go along with their non-F marked FSB. Milspec carry handles like Colt, BCM, PSA and others have taller sights (you can see the difference if you compare the carry handles). You can fix this for free by reindexing the carry handle about 15 clicks below their setting for 6/3. Google RIBZ or IBZ for more on how to reindex. Anyway, fixing the rear sight is the way to go, not putting on a short front post (which won't work with a flip up rear BUIS if you go that route later, which many of us do).