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Discussion Starter #3
I heard from a horse's mouth that the FN USG rail has built-in iron sights: a rear hole about the size of the 0-2 AR-15 rear aperture, and a front post that can be adjusted for elevation!

If it comes with the correct screws, I might just get it for the iron sights if the scope sits too high over the bore.
 

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metroplex said:
I heard from a horse's mouth that the FN USG rail has built-in iron sights: a rear hole about the size of the 0-2 AR-15 rear aperture, and a front post that can be adjusted for elevation!

If it comes with the correct screws, I might just get it for the iron sights if the scope sits too high over the bore.
Here ya go:


-TH
 

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Discussion Starter #6
mrtman is coming out with a $100 rail. Decisions, decisions!

The FN site says the USG rail BUIS is adjustable for windage/elevation. I have not seen a USG rail, but I'm guessing the windage adjustment is done as on the MC-10-80, while the elevation is adjusted via the front post.

Should I get the FN USG rail or mrtman's rail?
 

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Discussion Starter #11
I made a mockup of the USG rail setup to calculate the MoA "size" of the iron sight, and it will be around 15 MoA.

As a comparison, the standard BUIS on the PS90 is 22 MoA.
The M4 carbine w/ a 0.050" DCM post is 12 MoA.
The rifle length AR15s w/ a DCM post is 9 MoA.
An AK Carbine is 9 MoA as well (due to the distance between the eye and the front post).
 

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Discussion Starter #12
Interesting enough, the standard M4 carbine front sight post and distance from the eye equates to a 16 MoA signature.

If the USG Rail uses a 0.050" wide front post (it appears to be about this size from the artists rendering, LOL) the signature will be around 15 MoA or close to that of the M4 carbine. If the M4 carbine standard iron sights are good enough for the Army to qualify out to 300m, then I don't see how the USG rail's BUIS will be any worse.
 

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Discussion Starter #13
Someone who owns a USG rail got back to me on the measurements. he said the rear aperture is about 1/16" in diameter (I suppose he used a ruler to measure it), which is comparable to the rear notch on the PS90 BUIS. He said the front post was about 1/16" wide as well.

That equates to roughly a 18 MoA front post but I suspect the front post is probably a tad thinner.

This isn't too different from a M4 carbine standard sight. Ironically, the AK has only a 9 MoA wide front post due to the LONG distance from the eye!

Is the USG rail worth $140-$150? I'm not sure. If the BUIS is really decent, it might be. The Halo Tri-Rail and Magazineparts optics rail look to be very solid and durable products with a shorter height over the bore but you'd have to rely on the quirky PS90 BUIS, which isn't windage/elevation adjustable and is probably way off target, if your optics failed.

:?:
 
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