In my collection, I have five clam shell double rifles, 9.3x74R, and .450 nitro, and have seen ones in other calibers, including .405 Winchester, .500 nitro, even .600 nitro. All of mine are rat trap tight, and have never been put back on face by anyone. The clam shell action, to me, at first, wasn't too appealing, but they eventually grow on you after owning them for a time. The clam shell action, especially with square Greener crossbolt, is hell for stout, obviously made that way by the Germans in order to stand up to years of heavy hammering from firing; they succeeded immensely.