It's cast 6150 steel.
The original two hawks had them cast to keep a consistent weight between heads for matched sets and competition throwing. Devin probably kept everything the same.
To answer the OP, anything cast can have casting voids, which is why a forged piece -- hand or machined forging -- is preferable as it ensures no casting voids exist. Same with billet heads using stock removal to shape the piece.
That being said, I had the larger Voyager hawk from Two hawls, and my only complaints were that the haft is very thin, I had to wrap it to fill my big hands, and the haft was too short for my tastes. The head itself was perfect. The belt loop is made by a different company AFAIK, I forgot who it was, but you can buy 2Hawks hawks directly from them, and they offer the belt loop as an accessory. So if there's a problem, I'd say it's a matter of the other company, not 2Hawks.
