Demolition Ranch puts some science on it:

My first experience with magnesium was when I had one of those fire starters when I was in grade 9. I brought it over to my friends house where we spent like 30minutes making a big pile about twice that size on his math textbook.  We then sparked it, thinking it would be kind of boring… nope… huge flash, lots of smoke and a big hole in his textbook.

Demolition-Ranch-ENDO4:52 – Honestly I had no idea those 5 things on the Demolition Ranch shirt he always wears are all shotgun shells.  I guess it makes sense in hindsight, but they definitely could use some more detail.

Thoughts?  Anything else besides magnesium that looks cool loaded in a shotgun shell?