Hahn Precision BUIS vs. BCM upper

AR/M4 AR Technical Discussion
1

I just received my Hahn rear sight (http://www.hahn-precision.com/armory/products/buis_rear.htm) and am experiencing interference upon installation. Either the BCM reciever is out of spec on the large side, or the sight is out of spec on the small side.

This is the only M1913 spec I could find in a quick search: CLICK

According to that image, the rail is too wide on the top surface, but not overall.

Anyone else experience issues with either or both of these components? I just want to make sure I’m not a dumbass before I call Hahn or Bravo Company tomorrow.

Advise is appreciated.

2

Tested the sight out on two Stag uppers, and the one BCM. It didn’t fit on any of them.

Disappointed. :frowning:

3

hmnn…

looks like a nice low profile BUIS. Are the screws intended to go in between the raised protion of the rail on the picatinny?

did you back out the screws before attempting to mount?

4

How did it not fit?

5

I’ve heard they tend to be a rather tight fit. What was the resolution on this? I’m considering one of these for a build I’m currently working on.

6

Dustin Hahn told me that he opened them up a few thou more than a year ago because they were sometimes a bit tight. My first one needed to be lightly oiled and tapped into place, but the three I’ve bought since were all easy to install. The first (tight) one was on a BCM upper, and the newer three are on two different DD uppers and another BCM.

7

is this low enough to fit under a scope?

8

As you know, it depends a lot on the scope mount/ring height and the scopes ocular diameter with the lens cover installed.

9

I’m measuring 18mm to the highest point of the BUIS off the top of the rail.

10

thanks…

11

Same thing happened to me on the first one I purchased. He sent me another.

12

I have a hard time believing that the BCM is the problem. BCM out of spec would be like finding 26 cent quarter.

13

:wink:

C4

14

Look at the date of the OP and my recent comment…