Trouble with lead, is different alloys melt or become nicely fluid at different temperatures.
Thermometers should, I feel, be used as Jerry suggested - or trial and error using your lead pot
will likely do as well - with earned experience.
Of course the "trouble" (trouble?) today, with this information highway, there is always someone
who has learned 'the hard way' but is willing to share their experience (without charge - some do) so
you can learn the easy way and escape the heart or headaches of the learning curve. It gets to the point,
where people actually begin to expect to be told "how to do it", thus they actually never learn the HOW
method, which usually has MANY hidden lessons within the journey.
Thus, the easy way is not always the best method, perhaps, in the quest for knowledge & understanding.