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Posted: 12/7/2022 12:40:28 PM EST
[#1]
First off, the A2 does not have a detachable carry handle. That aside, you need to provide pertinent information as to the position of the rear sight and the range you are trying to zero at.
All military iron sights were designed to be zeroed at 25m. |
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Posted: 12/7/2022 2:07:07 PM EST
[#2]
Factory new gun? If not, disregard the following.
Guaranteed it shot straight when it was test fired. Are you familiar with the term “mechanical zero”? Return the sights to mechanical zero and try it again, being as precise as you can can with sight alignment and sight picture. I have unboxed hundreds of factory new issue Colts and some FNs and never had one that wasn’t on paper from the test fire. Once in a soldier’s hands, though, all bets were off. 
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Posted: 12/7/2022 2:37:32 PM EST
[#3]
No, it's a build; FN lower, FN flat top upper, FN detachable carry handle, 20-inch FN barrel F front sight tower.
At 25m with a mechanical zero, it shoots way, way too low. I have to lower the front sight until it bottoms out (I can hardly see the post) and raise the rear sight to get it close. I replaced the original (new) FN barrel with second new one...same problem, I also tried a 2nd detachable Colt upper, same problem. As per GI instructions, I would like to zero the elevation by only adjusting the front sight post. |
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Posted: 12/7/2022 5:03:14 PM EST
[#4]
The post has about 20 MOA of travel below deck, correct? And I assume you're raising the rear sight at least 5 MOA? That's about 1/8", so I doubt lapping the receiver face will help much.
What target and sight picture are you using? |
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Posted: 12/7/2022 7:33:36 PM EST
[#5]
Try to post pics of the front and rear sights......if you can.
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Posted: 12/8/2022 8:56:51 AM EST
[#6]
Quote HistoryQuoted: The post has about 20 MOA of travel below deck, correct? And I assume you're raising the rear sight at least 5 MOA? That's about 1/8", so I doubt lapping the receiver face will help much. What target and sight picture are you using? Thanks for responding... I am using a 25-meter Zeroing Target M16A2/M16A4 using the 6/3 setting, sandbag w/ 6-oclock hold. From what I have read... (?) the detachable handles (.825 GI shelf) should zero (be compatible) with an F front sight post. |
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Posted: 12/8/2022 9:10:57 AM EST
[#7]
Replace the upper receiver, since it has the same problem with more than one barrel. I assume when you said, “detachable Colt upper” you mean the carry handle.
Or try this, might not be enough. $11, give it a shot. Link |
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Posted: 12/8/2022 9:35:13 AM EST
[#8]
Quote HistoryQuoted: Replace the upper receiver, since it has the same problem with more than one barrel. I assume when you said, “detachable Colt upper” you mean the carry handle. Or try this, might not be enough. $11, give it a shot. Link Yes, sorry I meant FN and Colt detachable CARRY Handles... sorry too much caffeine. You may be right, it may just be the flat top upper... the current upper is FN, marked with the FN logo on the back end. The front sight needs to be lower, not higher. Would milling down the "F" front sight base .040" to standard specs be a viable option? |
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Posted: 12/8/2022 9:54:49 AM EST
[#9]
Quote HistoryQuoted: Yes, sorry I meant FN and Colt detachable CARRY Handles... sorry too much caffeine. You may be right, it may just be the flat top upper... the current upper is FN, marked with the FN logo on the back end. The front sight needs to be lower, not higher Oh, yeah, not sure why I was thinking backwards. Seems like that upper has to be the issue. Was it some kind of blem? |
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Posted: 12/8/2022 10:00:17 AM EST
[#10]
Quote HistoryQuoted: Oh, yeah, not sure why I was thinking backwards. Seems like that upper has to be the issue. Was it some kind of blem? Upper is, new FN.... I am going to measure and compare it to another one I have |
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Posted: 12/8/2022 10:08:24 AM EST
[#11]
Quote HistoryQuoted: Upper is, new FN.... I am going to measure and compare it to another one I have Why not just swap the other one in? |
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Posted: 12/8/2022 10:20:23 AM EST
[#12]
Quote HistoryQuoted: Thanks for responding... I am using a 25-meter Zeroing Target M16A2/M16A4 using the 8/3 setting, sandbag w/ 6-oclock hold. From what I have read... (?) the detachable handles (.825 GI shelf) should zero (be compatible) with an F front sight post. There should be a 6/3 setting on detachable carry handles, not 8/3. |
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Posted: 12/8/2022 11:46:26 AM EST
[#13]
Quote HistoryQuoted: Why not just swap the other one in? Its already on a barreled upper, I'll have to buy a new one. |
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Posted: 12/8/2022 11:50:56 AM EST
[#14]
Quote HistoryQuoted: Its already on a barreled upper, I'll have to buy a new one. Sounds like you’ve ruled out the barrel, and ruled out the sights, and it’s been apart and back together so there’s probably not some glitch from when you assembled it, so the upper being defective is just about the last remaining possibility. |
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Posted: 12/8/2022 6:50:55 PM EST
[#15]
Quote HistoryQuoted: Sounds like you’ve ruled out the barrel, and ruled out the sights, and it’s been apart and back together so there’s probably not some glitch from when you assembled it, so the upper being defective is just about the last remaining possibility. I took it to a friend's gun shop, these guys are very good, lots of builds and class III stuff. Measured the height of the FN upper, same as three others in their shop. They could not figure out the problem...I guess the only "fix" is to bottom out the front sight and raise the rear one. Thanks for everyone's input! |
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Posted: 12/8/2022 9:40:43 PM EST
[#16]
So far on my three flattops, three different scopes and mounts needed about 10 MOA up from mechanical zero for 100yds.
Do you have an optic you could use to compare the adjustment needed relative to irons? |
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Posted: 12/8/2022 10:05:41 PM EST
[#17]
Can you post a pic of how the rear sight is set?
Start with the front sight like this  You're supposed to bottom out the rear site to the lower 6/3 position, then go clockwise + 2 clicks (there might be a 'Z' there). Make sure the small aperture is up. After zeroing at 25, go back down -2 clicks to 6/3. Confirm at a longer distance if possible. If you can't confirm at 300, at least confirm the windage at 100  |
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Posted: 12/8/2022 11:57:09 PM EST
[#18]
I just saw that you said you're using a 6 o'clock hold. don't do that. you want a center hold (the top of the front sight post flush with the center line on the zeroing target)
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Posted: 12/9/2022 8:09:46 AM EST
[#19]
Quote HistoryQuoted: Can you post a pic of how the rear sight is set? Start with the front sight like this https://www.thefirearmblog.com/blog/wp-content/uploads/2022/09/20220912_145015.jpg You're supposed to bottom out the rear site to the lower 6/3 position, then go clockwise + 2 clicks (there might be a 'Z' there). Make sure the small aperture is up. After zeroing at 25, go back down -2 clicks to 6/3. Confirm at a longer distance if possible. If you can't confirm at 300, at least confirm the windage at 100 https://www.thefirearmblog.com/blog/wp-content/uploads/2021/06/M16a4-edit-4.jpg That's how I been doing it, at 25m using the target posted above. I currently can't go to the range, its hunting season here and COLD. Thanks again everyone for all the input. |
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Posted: 12/9/2022 6:15:16 PM EST
[#20]
Quote HistoryQuoted: That's how I been doing it, at 25m using the target posted above. I currently can't go to the range, its hunting season here and COLD. Thanks again everyone for all the input. In your previous posts you said you were on the 6/3 setting and using a 6 o'clock hold. You should be on the 6/3+2 setting (z) and using a center hold |
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