It can also be a bit of a pain to get all of the pellets to melt down for a smelt. Sometimes, the graphite coating hardens (possibly around some factory coating) and creates a protective "shell" around the lead. I have had a few of them pop and splatter, and I usually have to 'crush' the shell on about a couple dozen per pound.
Years ago, I had this happen also. I could not figure out why the shot would not melt. Discovered that the "crust" would not melt, but the lead alloy inside was melted...I had to crush the pellets with my ladle against the side of the pot to get the lead to pool in the bottom of the pot. Pain in the butt.