Ya beat me to it!
To get your HP's to expand properly and not shatter, it is a balance of lead hardness, velocity, and the size of your hollowpoint. ALL of these must be taken into account.
As Snuffy has shown, cast HP's can be extremely effective.
Most people try to drive them too hard with an alloy that is too hard which essentially makes them frangible and they retain very little of their original weight. (How do I know this....??
I don't know if Snuffy chrono'd those loads, but they were probably moderate loads. PLUS, he said he used an alloy that was pure lead (or really close).
Remember, softer bullets deform and trend to stay intact better than a harder boolit which can be brittle and fragment upon impact (if driven too fast).
SO, I hope this helps. I am BY NO MEANS an expert in this area of casting (or any other area for that matter). This should get you started.
BTW, make sure you use a decent lube and size your boolits appropriately. With lower to mid velocity loads I prefer to use a softer to medium soft lube. I have actually found BAC Lube to be great for just about every load I shoot (from 32 acp to 454 Casull). Others have had great luck with C-Red. I have used it, and it is a touch harder than BAC. Here is a link. It is cheap and it WORKS!!!