i have barely read this topic... and from what i HAVE read, and seen in videos by VERY TRUSTED and VERY SMART spudders, i am 100% COMPLETELY AGAINST this stupid idea of a flour filled bottle.
from what i KNOW from personal experience, if you shoot an empty bottle at someone, even witht he slits in it to make it "compress" it will still do some pretty hefty damage.
now, by adding weight of flour to it, it's going to do way more damage.
your concept idea is to shoot it NEAR the person, and have them get covered in flour, HOWEVER, at those velocities, even the lowest possible velocity next to hand throwing the thing, you can still get some damage done to your bare skin from the flour spraying out.
and one more thing you NEED to take into account here, you cant be sure where the person will move.. what happens if someone moves directly in front of it while it's in transit, not knowing that it's coming at them, and you nail them in the head?
are you willing to murder your friends, and then go to jail for that?
as stated before me... the ONLY remotely safe way to launch a flour grenade is to shoot flour only, not flour inside of something, as this will be way too dangerous.
by shooting flour itself it will disperse into the air, and spread out, at the same time it will slow down considerably and coat the person in the stuff. however, you would need to be considerably closer to them to hit them with it.
so basically... good concept to start with, stupid idea overall.