Cast vs Forged vs Investment forged
When I was at Smith & Wesson all gun parts stanrted out as round steel bars, cold rolled. The frames were forged, other parts milled.
In forging, the billet is placed into a die and hammered to shape. Forging is supposedly the best method for developing the grain in steel.
Casting is simply pouring molten metal into a mold, the same as making candles or popsicles. Its economical, efficient, but not for the best of parts/finishes.
Bill Ruger learned of investment casting during World War II. In investment casting, a wax model is used to form a ceramic mold. Molten steel is poured in, melting the wax which escapes through a vent. This forms a vacuum in the mold and arranges the grain structure very much like forging.
Investment casting produces steels nearly the equal of forging, and less expense.
Probably told you waaay more than you wanted to know.
P.S. Casting or forging are only first steps, milling, or machining, steps are required to finish the part.