I have one of these.
http://www.sportsmansguide.com/net/cb/cb.aspx?a=328392
It has three pockets, it's designed to have your sidearm in the pocket nearest your body with the hydration bladder in the middle pocket. I find it better to reverse them so the sidearm is in the middle.
In it's original configuration it's slow and loud to access due to lots of velcro and little clearance from your body. The middle pocket is a zipper and loads faster to get into.