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.