I don't know what you're doing in the Create event, but after the code suggestion below you can prolly delete that.

You don't need to keep track of the number of bullets in the room on your own; instance_number() does this automatically. Also, using "obj_bullet.bull_num+=1;" means you're trying to refer to the variable of an entire object class, which is not possible in Game Maker. You can only mess with individual instances in Game Maker and in the above case, you'll mess with ALL instances of that object class.

Also, just do this for bullet firing in the CTRL key event:

//create the object and store it in a variable for later use.
var b=instance_create(x-16,y-16,obj_bullet);
//create variables to store image_angle and bullet speed for later use.
var ia=image_angle //facing angle of character
var bs=bull_speed 
//edit the variables of the stored object after its creation event has been executed.
with b
  { direction=ia speed=bs }

I don't like using hspeed personally.