Dropping the hammer should not effect the slide/barrel from going foward (off). When the slide goes more than 1/8" foward, then the hammer will prevent the slide from going back on.
A lot especially new guns have trouble geting the slide off the first couple times. The head of the recoil rod digs a little ditch in the aluminum frame.
when that occurs, the slide must be forced off the frame. one method is to pull the slide back and let go, but since you pulled the trigger that is not possible now.
You will need to "hammer" the slide off the frame, for the first 1/2". A soft blow plastic, leather, or wood mallet is best.
Now when going back together, just thumb the hammer back to the reset position before putting the slide/barrel back on the frame