It is just how the crane is designed. It is "thinner" than other designs to have a "thicker" frame in that area (under the forcing cone) and to make room for the front cylinder lock point, which is a lever in the crane that goes in the front frame notch. But the crane is still rock solid. I don't think you can find a more robust revolver than a Ruger GP100 in the 6-shots, .357Mag class of revolvers, expecially for its price. To have a stronger revolver you can try a Manurhin MR73 or a Korth Combat (good luck for the price)... Cylinder rattle with the cylinder unlatched means nothing.