I agree with FrankenMauser, especially since I am using a similar type burner. It does get MO PLENTY hot, you don't need to turn it up all the way either to get there. I usually only set the heat by watching the flames as I increase the gas once lit. As soon as it starts to lick where the sides rise up from the bottom edge of the kettle, I stop. There is no need to crank it up higher as your heat will not be doing much to melt the lead at that point.
Another thing that you should be mindful of is whether or not that lead has had any contact with water. Some indoor ranges use a water trap to help keep the lead dust down, and if it is captured in some of those bullets it can be very catastrophic if you add in some to a molten pot.
To be on the safe side, you can fill the pot about 3/4 full of the raw bullets, then heat that up slowly until melted. That should allow the moisture to evaporate before things get dicey. However I would still keep a lid on the pot until it's melted to be sure. Once you pour that up into ingots add more to the empty pot and heat that up slow as well. If you have never experienced the Tinsel Fairy you have no idea what a mess it can make or what a hurting it can put on you. Be SURE to wear proper attire and smelt everything down outside. Not trying to be the alarmist here at all, just passing on added info to help you out.