Forgings are stronger than most casting primarily due to the grain structure being aligned in the forging process and the material is more dense than a casting could ever be, That being said, there is no real reason a cast receiver would not be a viable alternative to a forging especially considering that injection molded polymers have gained a following. In my business we often do mold work for die casting and permanent mold foundries, I have performed destructive testing on several casting alloys that I would stack up against a forging and not blink an eye. We have parts produced from Al-Mag, an aluminum magnesium alloy, that has great potential as a lower receiver material, especially when it is cast near net then form forged, or squeeze cast, leaving minimal amounts for machining. Investment casting is much more costly than forging, die casting or pour casting but it allows for finer detail in the casting with minimal concern for draft, undercuts or costly shell cores. Many investment cast parts are very near net shape only requiring machine work on highly critical areas.