BodyVelocity based on a different part's orientation?

Hello, I would like to figure out how to get a part's BodyVelocity to be based off of another part's orientation. For example, if I wanted to make a fireball cannon fire a part, and I wanted it to travel starting from the position of another part and head from the orientation of that part. Like most guns in the toolbox section of the studio, the bullets fire realative to the guns orientation. Thanks!