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Posted: 11/2/2009 2:29:29 PM EST
I've searched on this and didn't find anything dealing with windage.

I installed a Troy rear sight on my BM this past weekend. The rifle is a BM A3 M4. I removed the carry handle and attached the BUIS on the upper receiver rail. In between the front and rear sights I also installed an EOTech.

The rear sight was secured using LocTite. The EOTech was turned off during zeroing.

I fired my first round using the new rear sight with the small aperture and it hit about 2 inches to the LEFT at 25 meters. I brought the POI on target.

I then switched over to the close range aperture to verify and I hit 2 inches to the RIGHT of POI.

I know rear sight aperture changes can result in elevation changes dependant on the sight. I have never seen this type of POI change in windage though.

What's wrong, me or the sight?

Link Posted: 11/2/2009 3:03:36 PM EST
On USGI rear sight, the large aperture is drilled slightly off-center to compensate for the threading - when you switched from small to large aperture, the sight moves on a threaded screw, so yes, there will be lateral movement. USGI sights compensated this by drilling the large aperture off center and Troy does not.

Troy BUIS is strong and locks positively, but I hate their apertures.
Link Posted: 11/2/2009 3:21:26 PM EST
Originally Posted By Lindy_Hoppin_Gun_Nut:
On USGI rear sight, the large aperture is drilled slightly off-center to compensate for the threading - when you switched from small to large aperture, the sight moves on a threaded screw, so yes, there will be lateral movement. USGI sights compensated this by drilling the large aperture off center and Troy does not.

Troy BUIS is strong and locks positively, but I hate their apertures.


So what would you recommend?

My situation sounds like an awful lot of POI shift at 25m. I can see some, but it's about 8 MOA. That sounds defective to me.



Link Posted: 11/2/2009 3:36:01 PM EST
[Last Edit: 11/2/2009 3:41:08 PM EST by Lindy_Hoppin_Gun_Nut]
That large aperture was not meant to be used out to 100 yards. If the threat is farther than 50 yards, you have time to shift to the small aperture. That's why I really believe that fixed BUIS with absolute co-witness is king for red dots.

The most immediate threats are those that are in the closest range - under 25 M. At 50 yards, the shift in POI is 4 MOA - that is not too much. Shoot at a silhouette from 50 yards with it and I'll bet you will do just dandy with it.

ETA: IMHO, that 8 MOA shift is probably partly you. I know absolutely nothing about EOTechs, but with an Aimpoint, when the sights are zeroed, my red dot would sit on top of the FSP when aiming through the small aperture. When I switched from the small to large aperture, there is a VERY slight shift that should not matter out to 100 yards. But when I shoot it, I can't hit diddly jack with it because the large aperture's hole is too large for me, creating way too much error in my part.

YMMV
Link Posted: 11/2/2009 5:39:14 PM EST
I say just pick an apeture (the small one, if you as me) and stick with it. Don't worry about flipping back and forth.
Link Posted: 11/3/2009 1:19:02 PM EST
Lindy's and Camaro822's comments noted.

I'm going to give this one bump and add a poll. I'll let it die after that.

Thanks.

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