My molds were made out of 1 1/2" angle, but only 5" long. Wish they were longer like OS OK's version. My "ladle" is an old enameled 2 qt sauce pan, getting enough lead in it to pour that much in one pour isn't a problem.
I made 1# moulds out of thin angle. Fiver has it right, use the thin bedframe material because even 3/16" holds too much heat and slows down the pouring process. I have to use a water hose on mine and not cool them too much so they still flash-dry after dumping the ingots. Don't forget to put a couple dgrees of draft on the ends so the ingots let go easily.
I give the ingots about 7 minutes to firm up before flipping them over to dump.
One thing that'll speed the process is to keep that ingot pot below 750ºƒ...once the lead has been fluxed and I'm ready to start ladling, I turn the heat down substantially. If anyone wants to just buy these moulds instead of making them, I have a contact e-mail of a guy named Joe Leadslinger, retired welder who makes them up in Oregon.
I don't know whether or not this is allowed on this forum so I'll hold that e-mail address back until I learn it's OK.
You can see Joe's work in this video...I had been using an old set of angle iron moulds that were made poorly, I got those years ago from a contact in another forum, they wouldn't sit on a level surface and remain level for the incoming lead pour...that aggravated me to no end.
When Joe announced that he'd be making ingot moulds, I jumped in with both feet and got the first order!