I would google around for info on casting with different fuel sources. Many years ago, when I was still new to this world, we were using acetylene(!!!!) to cast with. It was dirty and we were having miscasts. I started googling and found a father son duo who had a great article about casting with different fuels and found out real quick that acetylene should not be used
. We changed over to propane and oxygen. Natural gas should be fine also.
Spruing is the other big concern. Making sure you have big enough reservoir is key. Also keep in mind how your molten metal is flowing. I try to limit the mount of directional changes the flow has to make before it gets to the margins.