Can some of you tell me the differences between these rifles and the interchangeability of them? I know a Stevens 200 is interchangeable with a Savage, what about the Axis and Edge? Are they interchangeable? What parts are different? How are they different? which rifles are "modifiable"? The market seems to be flooded with Axis and Edge (probably a very good reason for this) but not with Sanages or Stevens. What are the differences?