Iron sights with flat-top receiver

[tudor128]

I'm sorry if this has been addressed elsewhere, but I'm having an issue after zeroing my AR-15.

I have a Bushmaster A2, but a friend who works for Double Star switched out the upper for an A3 receiver and carry handle (both made by Double Star.) I went to zero the rifle and lost track of how many clicks I had to move the front-sight post up to get back on target. The disk-shaped portion of the front sight post is completely out of the well and there is now a substantial amount of daylight between the bottom of the disk and the top of the well. The detent is engaging probably half of this disk.

I understand there is another front-sight post intended for A3's, but it seems it's only 0.04" taller so I don't think it would make much of a difference. Is this just a normal occurrence with A3's or is there a problem? FWIW, this will be a law enforcement patrol rifle. Thanks for any insight you can offer.

[Constructor]

I am assuming you have run out of rear sight adjustment as well? Bottomed out?
If you have it sighted in, the taller post will just lower the disk .040 which should get you full engagement of the detent so it will help IF you you are sighted in.

Some receivers are not square where the barrel extension is clamped to the receiver, depending on which way it is out of square the barrel will point toward the low or short side. Most custom shops know to square the receiver before mounting the barrel but companies that mass produce ARs just slap them together as fast as possible.