Chuck C
Minor correction. Barrels are hammer forged. This term usually does not apply to receivers.
Receivers are forged, cast or billet. Forged is formed to near finished shape while in the heated, near molten "plastic" state. Part is then finished machined. THIS IS THE BEST because the grain structure of the steel is oriented to the finished shape. Billet is a piece of bar stock. Part is completely machined to the finished shape. Next best, but grain structure is not optimum. Grain is linear due to rolling process of making the original bar. Cast is least desired method as castings are less dense and can be porous. Grain structure is random. Cast receivers are much cheaper to make because they don't require expensive tooling and equipment to make. Cast parts if high quality have many surfaces that require no machining at all. Ruger was the first to use this method in high volumne. Servicable stuff, but not the best. All things considered, cast has the least strength. Cast parts will be adequate in strength, if designed properly. Parts that are cast to the SAME SIZE as originally forged parts will not be a strong as forged one. All processes stated above require heat treating to obtain the desired strength and durability. If you have a choice, go forged.