Swf smaller, but same filesize! grrr!

Hi!
I have a sequence of jpeg´s and when i make the swf 500x600 its size is 551Kb…

right…so what i did next was make the movie size 170x250…made the MC of the secuence smaller, to fit in those dimensions…and pffff!
its still 551kb!! why? its a much smaller size movie…
i am sure i have done this before and the size has come down! or doesnt it?!

ok, any tips/help…thanks…

mike