Are size seven fishing weights bigger or heavier than BB's?
As far as weight goes:
bb < 1/4" steel shot < 3/0 split shot < size 7 split shot
Generally speaking, bbs are not heavy enough for anything beyond automatic use. Zero reports good results using bbs in zero darts with holes in the back but it should be noted that a zero dart is inherrently more front-weighted than regular micro stefans.