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9/22/2017 12:11:25 AM
Posted: 9/21/2005 7:23:01 AM EDT
I just bought a used A1 upper from CMMG. (Great services, thanks guys!) It came with the A1-style rear sight. I'd like to change the aperture to the A2 style. I know this can be done, since my 6450 came with this style aperture.

Is it as simple as buying the aperture (~$12) and swapping it out? Or do I need a new spring and such, too?
Link Posted: 9/21/2005 8:37:05 AM EDT
[Last Edit: 9/21/2005 8:37:33 AM EDT by 1911builder]
The A2 aperture can be installed on the A1. The A1 aperture can also be installed on the A2. You do not need any additional parts, unless, you lose something during the changeover. Charles the Gunsmith.
Link Posted: 9/21/2005 8:47:37 AM EDT

Originally Posted By macros73:


Is it as simple as buying the aperture (~$12) and swapping it out?





Yes, unscrew the old, screw in the new, and you are done. I've done it with most of my A1 uppers.
Link Posted: 9/21/2005 9:18:09 AM EDT
Thanks guys. Should I get the Colt part or the DPMS one? (Colt part is twice as expensive. But I don't know if there's any difference.
Link Posted: 9/21/2005 4:14:25 PM EDT
Depends on your budget. DPMS will work OK. Charles.
Link Posted: 9/21/2005 4:31:00 PM EDT
Link Posted: 9/21/2005 6:02:54 PM EDT
While you are at it, have the rear sight apart, let me suggest you also change out the rear sight drum with a Rapidex Windage Knob.

At the same time change out the round front sight post with an A2 square front sight post. It will give a sharper front post image.

Zero at 50 yds with the small aperture.
Link Posted: 9/21/2005 9:24:13 PM EDT

Originally Posted By Tweak:

drlling out the L ap on the A1 is also an option.


Shit! Why didn't I think of that? I'll do that.
Link Posted: 9/21/2005 9:41:11 PM EDT
Link Posted: 9/22/2005 5:02:58 AM EDT

Originally Posted By Real_estate_salesman:

Originally Posted By Tweak:

drlling out the L ap on the A1 is also an option.


Shit! Why didn't I think of that? I'll do that.



I doubt you will like the results of redrilling an A1 rear sight. Look closely and you will see that one or both apertures are not centered on the leaf. So once drilled larger you will have an out of round circle of metal surrounding the hole, and it drove me crazy. You will need to remove it for drilling anyway, so why not just change it out?!

The A2 aperture switch works out well and several of my A1's wear them. The Rapidex windage drum is useful because it gives you 1/2 minute adjustments, allowing a more precise zero. Reinstalling the roll pin is often easier using a pair of pliers to push it in, employing due care to avoid slippage and finish damage.

Paladin
Link Posted: 9/22/2005 5:10:38 AM EDT

Originally Posted By A_Free_Man:

At the same time change out the round front sight post with an A2 square front sight post. It will give a sharper front post image.

Zero at 50 yds with the small aperture.



Sometimes installing the shorter A2 front sight post will be a No-Go due to not being about to bring your POI down far enough at 50 yards when zeroing.

One advantage(?) of the older A1 post is it yields 4/5 MOA per click instead of 1 MOA (5 detents/rotation vs. 4 detents/rotation) allowing a closer elevation zero. And the handy DIY can chuck that baby in a drill, and reduce the diameter quite easily. Try that with a square post!

Paladin
Link Posted: 9/22/2005 9:03:46 AM EDT
The older post yields 1moa on a 20" barrel (or "Dissipator"). The newer A2 post yields 1.25moa.

Link Posted: 9/22/2005 1:19:54 PM EDT

I doubt you will like the results of redrilling an A1 rear sight. Look closely and you will see that one or both apertures are not centered on the leaf. So once drilled larger you will have an out of round circle of metal surrounding the hole, and it drove me crazy.

It's off-center on purpose to account for the fact that the threads move it slightly on the shaft when flipped back and forth. If you look you can tell that one is off center on the A2 you replaced it with too.

I'd swap out for the XS same-plane so that my zero didn't move when switching back and forth. The only catch there is that the small ap on the XS is bigger than the A1 or small A2 ap.
Link Posted: 9/22/2005 1:37:43 PM EDT

Originally Posted By Stickman:

Originally Posted By macros73:


Is it as simple as buying the aperture (~$12) and swapping it out?





Yes, unscrew the old, screw in the new, and you are done. I've done it with most of my A1 uppers.



Just make sure you remove the roll pin first.
Link Posted: 9/22/2005 3:46:43 PM EDT

Originally Posted By A_Free_Man:
The older post yields 1moa on a 20" barrel (or "Dissipator"). The newer A2 post yields 1.25moa.




Got lost in fractions, you are correct of course.

Paladin
Link Posted: 9/22/2005 4:10:48 PM EDT

Originally Posted By macros73:
Thanks guys. Should I get the Colt part or the DPMS one? (Colt part is twice as expensive. But I don't know if there's any difference.



If you get lucky, the DPMS A2 aperature will have threads in it.
The last one I tried DID NOT.

Randall Rausch
www.ar15barrels.com
Link Posted: 9/22/2005 8:00:36 PM EDT
I had three AR's with A1 uppers which I changed to A2 aperture, Rapidex knob, and A2 sq front sight post. I felt no need to go all the way to an A2 upper receiver. I did eventually switch these to flattops.
Link Posted: 9/22/2005 8:12:22 PM EDT

Originally Posted By Tweak:
you won't be able to get the opening as large as the one of the 0-2 but you can open it considerably if you have skillz.



Tweak just watched Napolean Dynamite...

Randall
Link Posted: 9/23/2005 9:38:42 AM EDT

If you get lucky, the DPMS A2 aperature will have threads in it.


Uhoh. I'll find out Monday. Oh, and sorry Tweak, I have no skillz. If the DPMS aperture isn't threaded I may have no choice but to try drilling anyway!
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