Been there done that on my Lyman mag pot , think it was a peice of rust ???
Took a big paper clip & bent an inch L in it used the little vise grips to hold it though & have a pan/ingot molds close at hand to handle all the melt !!
I got mine unclogged & unstoppable , no burns or bad spills , I empty & clean it `bout every 5th pot now .