Hi Mate,
I cast the first one using a plaster mould,even though I heated the mould before I poured the lead,it still cracked so the second one was done using the method on the plan.
It looks a long drawn out affair, but it really is pretty easy,I made mine a little oversize and used a Sureform to take it down to the final size and weight.
The Wee Nip is pretty popular in our club (Glasgow Richmond MBC)and a few other local clubs are getting in on the act too,for this reason were going to make our own bulb mould,the former is already made
Definatetly check out the links left by Gingyer above as they give some good building tips.