You know, I am pretty new to casting bullets, in fact have only done about a hundred so far and shot none of them yet.
Just wanted to toss this in here with your extraordinary bullet, since it could easily happen to some other unsuspecting smuck like myself, who seems to get these little life lessons the hard way.
I have been melting lead for quite a few years to feed my surf fishing habits. As such I generally melted down about 20 or so pounds of lead at a time then poured up my weights while I had it good and fluid.
Well one sunny afternoon I was preparing for a trip the following weekend, had the pot set up on the fish cooker melting away out back of the house. Mid spring, early summer, not much difference around here along the Gulf coast. Just about into the third or fourth weight, I get a rush of cool air from around the corner of the house, and without warning over comes one lowly cloud with enough rain to really mess up my afternoon. The worst thing was, that I had set up the cooker just close enough to the eave of the house that the downpour was running into the pot. I only had enough time to kill the bottle before all hell completely cut loose.
What happened during the next 2-5 minutes was just short of something seen on National Geographic. There was lead exploding upwards of 8 feet into the air, and all I could do was stand WAY back and watch. When it was over the ensuing mess would have made the boldest tagger jealous.
So from then on fumes or not, I do all of my melting no matter how large or small inside, with enough fans on me to ensure no sweat builds up.