Working with hitTest

I am trying to understand the hittest and could use some help. Here is the code i used:on (press) {
on (release) {
//see if in center of target
onClipEvent (enterFrame) {
if (this._parent.target_mc.hitTest(this._x, this._y)) {
this._x = _parent.target_mc._x;
this._y = _parent.target_mc._y;
this._parent.target_mc._alpha = 50;
It works fine but I am trying to figure out onhow to make just the front of the bulet works on the center of the target.Als how can I stop it from jumping into place like it does?