I did have something relevant to add to the thread. A few days ago I was surfing the web, looking for something else, and stumbled upon S&W's patent for the Scandium alloy handgun. (Was actually looking for S&W patent on the M547's extractor. And "yes", it's there too). If you want to learn more about Scandium alloys it's all there, in excruciating detail. (Along with one of the better S&W revolver cutaway drawing I've ever seen. The name of each number item is in the Patent abstract itself).
Scandium containing aluminum alloy firearm
Here's another patent for just one aspect of the two-piece barrel.
Firearm frame and barrel assembly, method of assembling and assembly tool