Zebbi
You could try to tune the parameter of bullet behavior (max speed, or max rotate angle), then find out that the LJpotential behavior won't work well anymore. It needs tune the parameter A,B,m,n, too.
A possible solution is,
1. tune the behavior of the target object (bullet behavior in this case)
2. tune the parameter A,B,m,n of LJpotential behavior to match your requirement