Iron Sight Problem

AR/M4 AR Technical Discussion
1

I put together an Aero precision lower along with a BCM Standard 16" middy flat top with a Mil-Spec F-Marked Forged Front Sight Base.

Bought a Troy Folding Rear Battle Sight.

Sighted in with the EoTech and it works like a charm.

Then I tried out the irons.

Seems like I have to cheat under 100 yards. I have to really get my cheek down lower than I’m used to using the carry handle sights on my Bushy.

I’ve moved the front post way down in the FSB. Instead of having the front post in the middle of the rear sight, I have to have it about 1/4 the way up from the bottom of the rear sight.

If I use what I refer to as a good sight picture my POI is way low. If I use the bad sight picture I hit the bullseye.

Any idea what I’m doing wrong. Is this rear BUIS too tall?

And in case anyone asks, I started shooting at 25 yards, then 50 and then 100. The type of results were the same at each distance. But more pronouced as distance increased. And I was using the larger aperture on the rear BUIS at these close ranges.

Thanks.

2

This sight?

So you actually adjusted the front sight post all the way down…

Sight it in with the small aperture. It’s more accurate and easier to zero with.

I don’t think there should be much difference between your ‘good’ and ‘bad’ sight picture. How far off are we talking for your POI?

3

That’s what I was attempting to do.

But the sight picture was not what I expected.

I zeroed it with the EoTech easily, but with the irons I had to use the “bad sight picture” to zero it at 50 yards.

4

Are your Iron sights and EOTech set up for co-witnessing?

If so, when you turn on your EOTech is the red dot sitting on the front sight post as you look through the, small hole, rear sight?

5

At 50 yards I think the POI difference was about 6 - 8 inches low but I’m guessing. This is hard to explain but it seems like the rear sight is too high.

I’ll try the small aperature next time and see if that helps.

6

that would be a yes.

7

Try using the small apeture the next time you go out.

Explaination of how the sights work when you make adjustments.

[u]Front sight[u]

Front sight is for elevation adjustments only.
To raise the impact the sight needs to be turned clockwise
To lower the impact the sight needs to be turned counter-clockwise

[b]Rear sight/b

The Trot rear sight (flip up) adjusts for windage only.
you turn the rear sight in the same direction you want your impact to go.
Clockwise moves your impact right.
Counter-clockwise moves your impact left.

Rear sight height.

A taller rear sight raises your impact
A shorter rear sight will lower you impact.

A2 rear sights you can ajust for both elevation and windage

A1 rear sight windage only

I hope this helps

8

:slight_smile: My problem doesn’t stem from a misunderstanding of how to adjust the sights. Just guess I never noticed the small and large aperture were off center of each other.

This is the first time I’ve used a BUIS, always used the carry handle sights previously.

9

Great. I think using your small apeture will solve your problem.

Let us know how it goes.