Re: "80%" lower receivers
Maybe I missed something, but metal grain structure and strength are hugely different between CASTINGS and FORGINGS.
And it seems to me, that those pictures look like castings.
As was described earlier, during the forging process, the grain of the metal is aligned, and re-directed around contours and boss's. Whereas with a casting, the cavity of the mold is filled with liquid metal (molten) and the metal fills the voids like water in an ice-cube tray. (READ: no grain structure) Which is why when they break, it is 'random crystalline structure'.
Now, castings can be sorta 'forged' by taking the hot castings and pressing them between two dies. That 'sorta' aligns the outer grain structure, a bit, but not all that much.
So, as I said to open this post, did I miss something?