Guys, just completed a trade with a fellow member. I am the proud owner of a used A2 upper, it says "B MP 5.56 NATO 1/9 H BAR". (Any help with that would be appreciated; I'm kinda new to this AR thing.) I have a question regarding the rear sight. It is a bit movable, it can wiggle a bit with the rearmost edge turning toward the ejector side of the upper. It stays in that position; even returns to it naturally when I twist it, trying to straighten it up. Is there any way I can straighten it, and get it to stay straight?

Thanks, Mikey D...

The Bmp on the barrel stands for Bushmaster.

The rear sight housing uses only one side spring to twist the sight against a left edge of the upper.  This keeps the sight tracking true, and is normal.  If you tried to make the rear sight straight (inline) with the receiver, then as you raised the sight, it would not track correctly.

Note: ther is systems/rear sight housing that have been modified.  Instead of the edge tracking the upper receiver, two pins are added to the sight housing/receiver for tracking.  This keeps the sight straight with the receiver and allows the sight to track true on the pins when raised or lowered.  The draw back to this is the system/modifcation runs around $100 and must be done to the rifle by a smith (no Upper till you get it back).