FWIW on firecrackers...
It may be labeled M50, M90, M100, M1000, or M-zillion. Makes little or no difference AFAIK. Consumer firecrackers in the US are permitted a maximum of 50 mg of powder (no, it's not blackpowder). No doubt some imports stretch the limit a little, and the precise composition used probably makes a little difference. (All the crackers I've ever bought clearly contain a bit of something that increases sensitivity and produces an unmistakable odor.)
And possibly a heavier-walled tube increases confinement and loudness of the report.
Regardless, the M in the name generally stands for "marketing".
Best,
Terry