Okay, this is what i do...see if it makes sense:
1. clip a loaded paint brush in a little clamp so that it's bristles are pointing straignt up.
2. stuff a little piece of sticky tac on the end of the bomb behind the fins (like where fuel would fire out if it was a rocket instead of a bomb)
3. jam a pencil firmly in the sticky take giving you a bomb on stick much like a corndog
4. hold the corndog bomb by the end of the pencil perpedicular to the brush with the bristles touching the bomb where you want the stripe
5. rotate the bomb by turning the pencil.
If you use a flat brush, you get a nice even stripe around your bomb.