Stored Energy Devices?

[K.Porter]

Since the Q&As aren't open yet, I'm turning to you all for an opinion here.

My team has been contemplating building a slingshot or other projectile device to hurdle the track balls, using springs or bungees, or similar. I know that the FIRST rules don't specifically prohibit this, and in regards to stored energy devices FIRST states simply that teams "must be very careful" when installing springs, etc.
Since the track balls are very heavy, it would take a rather large slingshot to get them moving at any real speed, and while I'm confident that we could design such a device, I'm not so sure how the FIRST judges would react.
For teams that have used stored energy in springs or similar previously, has anyone had trouble with the judging? And I suppose for those of you who have been at this longer than I have, do you think such a large slingshot idea should be cause for concern?

Thanks.