Thanks for all the thoughts, PhilOhio. I have indeed thought of some of these things, but it's always good to get even the same thought from a different set of eyes.

As to the fit of the adapters, they already are pretty "hollow" down their center. They really index at their edges, mostly against the wood of the grips. But the idea of using silicone to fill in between the adapter and the frame is an interesting one. It certainly seems like a low risk proposition for anyone who wants to try it.

I have discussed the powdered aluminum approach with my materials supplier. That is indeed an available option, with materials available from their catalog. But it involves a more complex routine for preparing the mold for each pour, requires a mold dedicated to cold casting of the particular metal involved, it takes 24 hours to cure, and then requires polishing the demolded part to get down to the embedded metal. So, significant mold expense for 1 part/day that still requires hand finishing. I sort of concluded that it wouldn't be the most profitable way to spend my time.

Thanks for mentioning the Dremel tool. As I already noted, the inside of the adapter is already hollow, so I don't need to sand or grind it out. But you remind me that I could put a small, side cutting mill in a Dremel and it might cut through the sprue easier than the Xacto knife I'm using now. Have to give that a try tomorrow.