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Am I going crazy? Windage change between small and large aperture
3/21/2012 4:58:43 PM
I've been out at the range several times this week trying to diagnose a rear sight problem. Here's what I'm using:
- Colt M4 Carbine with 16" barrel and 1:7 twist rate
- Flat top with carry handle / iron sight assembly mounted
- 50 yards' distance
- Standard XM855 ammunition (Green Tip)
When I zero the carbine with the large aperture and then flip to the small aperture, my impact point shifts up by six inches and left by four inches.
When I zero the carbine with the small aperture and then flip to the large aperture, my impact point shifts down by six inches and right by four inches.
So, it seems like switching between the small and large aperture doesn't just cause a change in elevation, but it also causes a significant change in windage.
What's going on? My groups are sub-MOA at 50 yards and I'm really pleased with the accuracy of the carbine. But this rear sight is driving me out of my mind.
- Colt M4 Carbine with 16" barrel and 1:7 twist rate
- Flat top with carry handle / iron sight assembly mounted
- 50 yards' distance
- Standard XM855 ammunition (Green Tip)
When I zero the carbine with the large aperture and then flip to the small aperture, my impact point shifts up by six inches and left by four inches.
When I zero the carbine with the small aperture and then flip to the large aperture, my impact point shifts down by six inches and right by four inches.
So, it seems like switching between the small and large aperture doesn't just cause a change in elevation, but it also causes a significant change in windage.
What's going on? My groups are sub-MOA at 50 yards and I'm really pleased with the accuracy of the carbine. But this rear sight is driving me out of my mind.
3/21/2012 5:11:43 PM
TAG
3/21/2012 5:21:23 PM
Yes, will be a change in elevation since the small ap is for the high number on the dial, and low number on the elevation dial for the large ap.
But the shift left to right should not happen, so the question comes down to if the ap is in the housing backwards?
As the ap is flipped from small to large, it chases the threads on the windage screw, with the ap's slightly drill off of each other to compensate for such, but if the ap is installed backwards, then it will be treading the wrong way for the compensation.
But the shift left to right should not happen, so the question comes down to if the ap is in the housing backwards?
As the ap is flipped from small to large, it chases the threads on the windage screw, with the ap's slightly drill off of each other to compensate for such, but if the ap is installed backwards, then it will be treading the wrong way for the compensation.
3/21/2012 9:11:34 PM
Off center aperture(s)?
3/21/2012 9:45:00 PM
Originally Posted By Dano523:
Yes, will be a change in elevation since the small ap is for the high number on the dial, and low number on the elevation dial for the large ap.
But the shift left to right should not happen, so the question comes down to if the ap is in the housing backwards?
As the ap is flipped from small to large, it chases the threads on the windage screw, with the ap's slightly drill off of each other to compensate for such, but if the ap is installed backwards, then it will be treading the wrong way for the compensation.
Yes, will be a change in elevation since the small ap is for the high number on the dial, and low number on the elevation dial for the large ap.
But the shift left to right should not happen, so the question comes down to if the ap is in the housing backwards?
As the ap is flipped from small to large, it chases the threads on the windage screw, with the ap's slightly drill off of each other to compensate for such, but if the ap is installed backwards, then it will be treading the wrong way for the compensation.
What type if rear sight do you have installed? This will help others to understand the problem. Since the issue is consistent with the only change being the sight flip, the problem is most likely there. Its entirely possible that you installed the sight backwards also which is creating the problem. (I'm not trying to insult you there. It has happened before and will happen again.)
3/21/2012 10:01:52 PM
Should have mentioned that in the initial post!
The rear sight is a standard Colt M4 detachable carry handle / iron sight attachment that screws onto a Colt 6920 M4 Carbine flat top with the two thumb screws. It has the "SQUARE" forge mark on the right side and is the "6/3" type.
A few ideas that I've posted on the other forums about this issue...
The hole for the small aperture is centered properly.
The hole for the large aperture, when viewed from the shooter's position, is noticeably drilled off to the right. However, it's my understanding that this is intentional and I have definitely seen this on a few different carry handle sights.
Should the large hole be centered as well?
I should also note:
Using the large aperture, the rear sight requires approximately four or five clicks of right windage to zero the carbine. Using the small aperture, the rear sight requires ten clicks of windage to zero the carbine.
I'm sure that my front sight base is canted slightly to the right. This should be why I need to make my initial windage adjustments. However, it doesn't explain why switching from the large ap. to the small ap. causes a change in windage again.
This really frustrates me. I've gone through a couple of these Colt M4 carbines recently, and each one has had problems in one area or another.
I've tried to contact Colt's customer service by phone, but I've given up after each attempt when 25 or 30 minutes' time has passed without reaching a human being.
The rear sight is a standard Colt M4 detachable carry handle / iron sight attachment that screws onto a Colt 6920 M4 Carbine flat top with the two thumb screws. It has the "SQUARE" forge mark on the right side and is the "6/3" type.
A few ideas that I've posted on the other forums about this issue...
The hole for the small aperture is centered properly.
The hole for the large aperture, when viewed from the shooter's position, is noticeably drilled off to the right. However, it's my understanding that this is intentional and I have definitely seen this on a few different carry handle sights.
Should the large hole be centered as well?
I should also note:
Using the large aperture, the rear sight requires approximately four or five clicks of right windage to zero the carbine. Using the small aperture, the rear sight requires ten clicks of windage to zero the carbine.
I'm sure that my front sight base is canted slightly to the right. This should be why I need to make my initial windage adjustments. However, it doesn't explain why switching from the large ap. to the small ap. causes a change in windage again.
This really frustrates me. I've gone through a couple of these Colt M4 carbines recently, and each one has had problems in one area or another.
I've tried to contact Colt's customer service by phone, but I've given up after each attempt when 25 or 30 minutes' time has passed without reaching a human being.
