neck ache

[conradin]

I have been practicing my AR a lot lately. I have developed a neck pain...is that normal, or is that a sign of a wrong posture? Pain develops when I turn my head while aiming.

[John Marchant]

Sounds like incorrect head position on the cheek-piece and the cheek-piece not providing enough support for your head. Increase the height of the cheek-piece.
Are you bending your neck/head position over to get in line with the sights, if so you need to try to straighten your neck up slightly and move the rifle and sights toward your aiming eye, which may mean shooting with a slight cant.