Why does loaded movie's width return 0?

programming flash
1 
swfLoader = new MovieClipLoader();
swfListener = new Object();
swfLoader.addListener(swfListener);
swfLoader.onLoadInit = function(targetMC:MovieClip) {
	trace(targetMC._width); // returns 0
};
swfLoader.loadClip("http://url.com/1.swf", this.containerBox);

Any ideas? I need to resize the loaded swf into the width of containerBox, and add some sort of detection to figure out when the loaded swf is finished (maybe using _current & _totalframes) to load the next swf (where process repeats).

Thanks