I ground the existing knob off and threaded it 5/16x24 with a quality die. I start by grinding it a little large and somewhat round, then I put a bigger die on it and get it rounded out perfect, then keep bringing the die size down until I hit the diameter I want. Takes a little cutting oil, a die and a dremel.
The coating on the bolt handle is graphite black Cerakote, the shroud is Tungsten Cerakote.
Yes. The infamous casting voids. They are there. I actually have found at least one void in every handle I have modified. They are usually small, about the size of a grain of salt. But some can be pea sized!