I embarked on casting bullets for an 8x57 military Mauser. I knew from the forum that measuring the throat was an important step. Pound casting is regarded as a good way to do so. Here is what I came up with.
The rod is .250 dia. drill rod. The end is capped with a slight press fit cap. Two spacers are a sliding fit on the rod and kept in place, equally spaced, with masking tape. The muzzle piece is also a sliding fit. The anvil is an empty case with a length of brass rod extending to the case mouth. Between the stiffness of the drill rod and the spacers the bore is protected. The outside diameter of the brass pieces is a few thousandths less than the bore diameter.
Next was getting the slugs. I made a mold from aluminum bar stock. The mating faces were fly-cut for a smooth flat surface. The holes for the brass alignment pins were match drilled and reamed. One block is taller than the other so that the hole can be accurately placed right on the joint between the blocks. After indicating the edge in, a spot face was made to give a flat surface to drill the hole on. The hole was then drilled. Not having a reamer I drilled undersize and then with the finish size drill, again just under the bore size.
I warmed the mold with a propane torch and poured pure lead from a ladle. The resulting slugs worked well. The length allowed the entire length of the long Mauser throat to be captured. The throat measured .3260-.3265. My Lee mold cast .327 in 20-1, so is useable without modification or sizing, a little bit of luck.