William,
Deputy has pretty well nailed it! One other way to check for fit and size is to take an UNloaded gun with the trigger in the set position. Holding the gun in the off hand, position the first joint of the trigger finger on the trigger. Without changing this position take a firing grip on the gun. Bring the gun up and check the sight alignment. Assuming you're right handed, if the front sight is aligned to the right of the rear notch, the grip is too large, aligned to the left it's too small. Works just the opposite for left handers.
Stay Safe,
Savage