I would echo some of the comments here.
1. Yes, the Minie needs to be made of lead that is as pure as you can find. The way it works is absolutely dependant on that skirt expanding easily and evenly.
2. I have a CW Minie, and the skirt on my example is actually fairly sturdy. The lead is soft enough to scratch off with a fingernail, but the skirt is thick enough that it would hold up under all but the roughest handling (i.e., stepping or falling on it).
3. The hundreds of rounds I put through my used one-in-forty-eight .54 caliber TC New Englander were all cast with a cheap Lee REAL bullet mould. I could pretty easily get 2" groups, and, similair to a Minie, I could shoot a bunch of times before a barrel swabbing was necessary. We cast our bullets using nothing more than an old cast-iron ladle and a torch for heat. A REAL bullet will also knock the absolute stuffing out of a deer.
Great thread! Very informative.
"Proclaim this among the nations: Prepare for war! Rouse the warriors! Let all the fighting men draw near and attack. Beat your plowshares into swords and your pruning hooks into spears. Let the weakling say, 'I am strong!'" Joel 3:9-10