One tip I have for putting the shrink tubing on the female bullets is to leave the shrink a little longer, then when you heat it up to shrink it, the tubing curls over the end of the bullet slightly. You can still plug & unplug the male into the female with no problems at all, but it means that if the 2 bullets on the battery should touch, there is no way the metal can actually make contact to create a short circuit. The best analogy I have for this is a bit grim though; think: foreskin...
