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Posted: 10/28/2013 10:52:18 AM EST
[Last Edit: 10/28/2013 10:59:10 AM EST by mdean2011]
Finally able to take out my SBR upper and test out its 25 yard grouping. First three shots at center dot on circle target where even in elevation, but 6 inches to the right of center with the windage dead center on my MBUS rear sight.
So, I moved the rear aperture over about one mark to the left and it is pretty much on target.


So now I have a few questions.

Is there anything wrong with my sights?
Would the barrel or upper receiver be bent slightly?
What exactly could I have misaligned on a standard barrel nut using a Troy Alpha rail? (from the EE. Did not put money in Troy's pocket.)
Is there any cases as to why my rear sight would have to be adjusted that extremely?

Not sure what to do or what is the correct answer. I've looked closely at my barrel and it doesn't seem bent.

What do you guys think?
Link Posted: 10/28/2013 11:17:41 AM EST
I don't think I've ever had the mechanical zero on iron sights ever be my true zero.
Link Posted: 10/28/2013 12:45:23 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By sgthoskins:
I don't think I've ever had the mechanical zero on iron sights ever be my true zero.
View Quote


I was just curious. My last upper had nearly perfect mechanical zero. Just seemed more extreme in adjustment I guess.
Link Posted: 10/28/2013 4:27:59 PM EST
Its very common for either the handguard (and the attached iron sights) to be very slightly twisted, or for a barrel mounted front sight to be slightly turned from top-dead-center.

Its nothing to be worried about, and adjusting the rear windage is the correct fix.

You should see my troy rear, its almost pegged left, but on my gun its easy to see the handguard is turned slightly.
Link Posted: 10/29/2013 3:37:41 AM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Chrome308:
Its very common for either the handguard (and the attached iron sights) to be very slightly twisted, or for a barrel mounted front sight to be slightly turned from top-dead-center.

Its nothing to be worried about, and adjusting the rear windage is the correct fix.

You should see my troy rear, its almost pegged left, but on my gun its easy to see the handguard is turned slightly.
View Quote


Good to know. And I readjusted my Troy rail to get it as straight and as even as possible. I was able to bring my windage back a little to the right. Must have just been off a very miniscule amount.


Thanks for the info.
Link Posted: 10/29/2013 4:06:51 PM EST
When I did my first build, I used front & rear BUIS. My front sight was atop a free-floated rail. When I first zeroed my weapon, it took around 12-13 clicks left from center to zero in at 25m. When installing my rail originally, it was just maybe a 16th of an inch, if that, canted to the left. After taking my rail back off, I kept adjusting my barrel nut's rail adapter until my rail's upper picatinny rail was perfectly aligned with my upper's picatinny rail. After doing so, my rear sight ended up needing to be moved back to center to be zeroed in at 25m. What got me to re-adjust my free-float rail was after reading page 0015-16, dealing with bore sighting, in TM 9-1005-319-23&P.

TM 9-1005-319-23&P
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