When buying an airsoft gun it is important to remember that an airsoft gun is designed to imitate a certain real gun. The airsoft gun will share many of the same features. Things like and ambidexterous safety, the type of mag release,and type of sights will all probably be shared with the real version, and be universal with airsoft guns of that type. Also look at the proportions of things like the stock, hand guard, and magazine. A large magazine will hold more ammo and a spacious hand guard or stock will potentially house a larger battery.