The BB throw was by far my worst event on the CFA. I think my best was my third throw at 57' or so. Not good.
Flyers is right. Try leaning back and twisting. Act like you're hitting a big tennis ball. The movement is very strange since you're on your knees. Keep your arm straight, tighten your abs, and try to 'flick' it. Act like a trebuchet (youtube to see in action). That helped me, but everyone is different. Try a bunch of different techniques and see which works the best for you.
My element leader in SS told us that the BB throw isn't looked at too critically because it's not on the PFT. Make sure your push-ups, pull-ups, sit-ups, and run are good though; they are on the PFT/AFT.