MathTeacher: Show us where you read that the newer receivers have different steel/heat treating. I have heard this rumor for years and no one can produce facts. It is the SAME receiver with MORE metal milled out to accommodate the longer cartridge length. I would be leary of any rifle produced before 1920, but due to testing procedures, not the grade of steel. I am to lazy to look it up, but think the .300 did not make the seen until at least the 30's. When the detachable magazine model was introduced, there may have been steel/heat treating changes. I simply do not know. The basic structure of the receiver was changed when this new model came out, so it is possible there were material changes.