Hey guys. I rarely post here as I'm basically a lurker taking in as much information as I can and learning as I go along, but I ran into an unusual situation today at the range and I'm curious to know if this is something to be concerned with or not.
Before I get into the issue...A while back I purchased a Magpul MBUS for my LE6920 as I had removed the carry handle in order to mount a RDS. Zero the MBUS at 50yds with the base of the front sight post flush with the top of the FSB. A couple windage adjustments and I was dead on without having to make any elevation changes. GTG.
A week ago...I got in a new BCM 14.5 mid-length upper. Now what I don't want to do, is move my red dot and MBUS from the Colt over to BCM since the 6920 is zero'd.
A year or so ago, I picked up a LaRue BUIS that I never really used...so I figured I would mount the LaRue to the BCM, zero it...and then whenever I can pickup another lower, I'll have another AR build to play with.
Here is the LaRue BUIS I'm referring too...
Ok...start out with base of the front post flush with the FSB, rear aperture (small) centered. Take 5 shots at 50 yds. In the picture you can see the first group at the top right...then you can see the adjustments as I walked in my rounds to the center of the target.
Now...this is what has me at pause...
My question is...is it normal for the front sight post to be this elevated after a 50 yd zero depending on what rear BUIS may be used? I was under the impression that rear sights be they folding or not...were supposed to be pretty close to the same height off the upper receiver...but I may be wrong. IDK.
Remember...the front post on my Colt needed no adjustment at all. It's still flush with the FSB and it's dead on at that same range.
What I may do, is mount the carry handle off the Colt onto the BCM and re-zero to see if there is a change.






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or just go ahead and see about getting a taller FSP. It just seems to me that if a taller post is needed...BCM should make that a standard.

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