You won't be able to melt a pot full. You might get about 10# up to temp at best. As I stated above, I use a 6" cast skillet, and I melt about 5# at the time. It will take about 5 min. to get to temp. Then you can add small amounts along as you cast or pour it up. Don't empty the pot once you start, or you will be starting over. Once all is liquid, pour a couple ingots, then add some more WW. Be careful fluxing, as you can get an open flame depending on what you use. I mention this in case you are going to cast indoors.
I found my turkey cooker at a pawn shop, and bought the burner for $15.00. I use the spare bottle for my grill on it. I can melt 75-100 # in just a few minutes, and just like above, never empty the pot, but keep some melted lead to hold the heat up.
This will give more lead than I can cast time wise, and if you plan to do this long term, the burner would be a good investment.
G.B. and some others have reported cast pots bursting with them, so I now use extreme caution with mine, even though I have used it for years. I am looking for a heavy SS pot, and when I find one at a flea mkt. or such, I will buy it.
Good luck, and good casting,
Ben