Why do you want your bullets to use physics behavior specifically? Will they need to collide and bounce around physically? If not then physics behavior shouldn't be used. The only time you should use it is if you want physics based interaction between objects. Using it solely for the purpose of vector based movement/inertia is inefficient; for that you should use custom movement behavior. In general you shouldn't combine two movement behaviors unless you're manually toggling between them for a certain reason. Physics behavior hijacks the x,y, and angle of an object, so adding a bullet behavior on top will just apply angle based movement to the object after its movement has already been physically solved and applied by physics behavior. Bullet behavior is dead simple, and is equivalent to the "move at angle" action, minus the time-delta adjustment.
The Physics behavior is how I modeled the Black Hole. By using the "Add Force Towards" action.
I was just trying to achieve the same effect with the bullets... If you shoot them past the black hole, they CURVE towards it, and/or get sucked in entirely. That way, during the game, you can do "Trick shots" where you aim near the Black Hole and the shot will angle around it and make a complete left turn (or whatever.)
So, is there a manual way to do "add force towards" using Bullet or Custom movement Behaviors?
I'll attach the file I'm working on (minus bullets) so you can see the "add force towards" effects.