Iron Sight Problem

[watertower]

Ran into a problem recently trying to zero the irons on a build. Using a Troy flipup front mounted on a Larue rifle length tube, 14.5" barrel and ARMS #40 rear sight, I cannot get the front sight post to go low enough to zero at 25 yards. The front post is bottomed out in the housing, and POI is 8" low.

My Aimpoint zeroed easily, so I believe it isn't in the upper assembly. However, with the aimpoint mounted, the dot shows up in the middle of the front sight as I'm looking through the rear sight. On a previous build, the dot was at least close to the top of the front sight as viewed through the rear sight.

At home I tried putting an LMT rail mounted front sight on it, and the Aimpoint was still showing up in the middle of the front sight post, with the post bottomed out. I believe this is an issue with the ARMS rear sight. I could cut the front post down so it works, but I'm wondering if anybody else has had trouble with the ARMS rear like this.
Thanks.

[Robb Jensen]

Is your ARMS 40 rear the one with the notched (flat spot) on the small aperture? I've experienced zeroing problems with ARMS 40s with flat spot small apertures. If you have any other rear sight try it (or a removable carry handle) and see if it'll zero.

Try for 1.5" low at 25yds and then POA/POI at 50yds.

[watertower]

Thanks Rob. I figured I wasn't the only one.

The ARMS reear does have the flat aperature. I've got a 40L I can try and a chopped carry handle I'll try out as well.

[tkoglman]

Try sighting in at 50yds instead of 25yds. A 50 yd. BZO gives you a flatter trajectory out to around 250yds

[EmanP]

Also make sure that you are centering the post of the front sight in the rear sight. I had some old style Troy fronts and I was actually putting the protective ears/circle inside the rear apperture and not placing the post in the center. The lower I dug the post, the lower it hit.

[watertower]

I understand the reason for using a 50yd BZO, but I'm also trying to be realistic in my approach to a self defense carbine and the distances that it would be applied to. I'm going to try 50 to see if I have enough adjustment to zero, and i may have to live with it.

I do believe I had the post centered, but I'll give it another try and really focus on sight alignment.