TexasCHLforum.com

Check and make sure that your barrel is on tight. Grab your upper receiver with one hand, and grab your A frame or gas block in the other, then give it a good twist. If it moves at all then your barrel is loose and it can cause a ton of issues. Also, sometimes the front sight can be bent, or even the barrel itself. And I dont want to link to another forum...but theres a post on 10-8forums.com that has GREAT info on mil-dot scopes, I will see if I can find it and post a link.

http://files.thetallengineer.com/Mil_Moa_Simplified.pdf

There you go, its a great informative read, a little long but it will explain the mil-dot system for you.