The most important issue is to fit the boolit to the throats (front of cylinder) for best
accuracy. You will do well with the 429421 but if that is harder to obtain than an
RCBS mold, the 44-250-K is a very good version of Elmer's design and their molds are
really well made, probably the most consistently nice molds of the production
companies. My SBH has very large throats (.432") and was a good shooter with
jacketed and mediocre with .429 hard cast commercial. With softer Keith design
boolits sized to .432" from an oversized mold, it is accurate.
Two very useful loads are the original Keith load of 20 (or so) grains of 2400,
and the ever popular midrange load of 10 gr of Unique. If you have Power
Pistol but not Unique, 9 gr of PP is a nearly identical load - about 1050 fps with the
250 Keith designs, which is accurate and not quite so "energetic" as the full
power loads, but will shoot thru a white tailed deer from end to end.
Hard alloys and GCs are not needed. Start with something like wheel weight alloy-
about 10-12 BHN as a starting point. Usually, this is all that is needed, but some
find better accuracy by increasing the hardness, something that I have not found
consistently.
Bill