In the video I did on two-hanged slinging, the ice blocks I was throwing were in the area of 1700g.  So I completely agree, 450 to 500g is definitely manageable.  I'm planning some more experiments with heavy projectiles so there will be more videos coming.

I got the drill bit I'm going to use to make some molds for lead.  It's this one: https://www.amazon.com/CO-Z-Large-Spiral-Groove-Drill/dp/B07CMPH9VY/ref=pd_bxgy_....  I figure if I drill out two blocks of wood and clamp them together, I should be able to drill another hole in the center to fill it up.  That's the plan anyway.  We'll see how it works.