Going overhead with weights can be difficult. I usually have to get super warmed up before attempting to OH Squat with any kind of weight. Having tight shoulders, tight hips, tight hamstrings there can be a number of issues deflecting you from acheiving a superior overhead position. In the post below, Kelly Starrett of Crossfit San Fransico addressess shoulder mobility by stretching the triceps.
Ummm, Your Overhead Break is On?