I have been using a BCM built BFH 14.5" ELW upper with the mod 1 flash hider and 13" KMR, on my duty gun for the past 1.5 years. It has served me well, and been accurate and reliable as expected from my experience with BCM.
But, since switching to a new white light mounting location (12 O'clock, in front of the DD fixed front sight) , I have noticed that the front sight post is almost completely buried behind the outline of the Streamlight TLR-1HL. Once zeroed, I can only see about 1/6" of the tip of the front sight, when shooting, and it really isn't practical to use the irons that way. I run an aimpoint T1, but the fixed irons need to work if the aimpoint goes down.
On other guns with other types of rails that I have assembled using the same DD front sights and Streamlight TLR-1HL, much more of the front sight is visible above the outline of the TLR-1's bezel outline. Like at least 1/8", which is adequte.
Looking around at my KMR upper, it appears that the locking clamp/screw design, pulls the rail upward, causing the upper reciever's rail, and the KMR's rail top, to not be in perfect alignment, but the rail is tilted upward somewhat. That upward tilt is what is causing my zero differences from other uppers using a DD front sight, and requiring the front sight post to be buried into the FSB more than usual, and thus hiding more of the FSP by the TLR-1.
I love the KMR and this upper, with the ELW barrel and mod 1 brake, but I likely will look for another rail, because running my light at 12 Oclock is a must for me now.
I wish BCM could come up with a dual clamp system, at the top AND bottom for these rails, so the rail wouldn't tilt upward so much. Or, better yet, just redesign it, to put the locking clamp system at the bottom of the barrel nut, not the top. A downward tilt would be better than an upward one, for those of us that like to run 12 o'clock white lights. Problem is, switching out rails on this upper is not simple either, since I can't remove the KMR barrel nut, without unpinning the mod 1 brake. Crap. A redesigned rail with the clamp on the bottom that would be compatible with the same existing KMR barrel nut, would be cool, but I am betting thats not gonna happen.
Anyone else notice the upward tilt of their KMR rail?