Hi Mike, I used to cast cartridge ammo bullets, but gave up since it was a royal PITA. First off, you need to mix the right alloy and lead alloy needs continuous fluxing. The bullets then need to be tested for hardness. Then the bullets need to be sized and lubed. I have found it much cheaper and less frustrating buying my lead cartridge bullets ready to go. As you know, I do cast all my pure lead projectiles.
BTW, I think that a bottom pour pot would crap up pretty fast with lead alloy contaminates.
I currently buy my lead alloy bullets from Oregon Trails, Speer, and Magnus.
Regards,
Richard