Back when TC was making Magnum receivers and modifying non-Magnum receivers one of the Custom Shop gunsmiths explained the difference between them to me. There is more than just cutting a slot in the bolt. He said there is no difference in strength, but under the higher recoil of a magnum cartridge the bolt of a non-Magnum receiver can move and the action can open. The bolts in the Magnum receivers are locked in place so they cannot move because of recoil. I have both non-Magnum and Magnum receivers and there is a easily seen difference in their operation. If one opens, that is, breaks over the barrel of a non-Magnum action gun, the opening lever springs back to the center position. If one does the same with a Magnum gun, the lever stays to the side. Also, either a non-Magnum or a Magnum gun can be opened by moving the lever either right or left.