In the 1911 when the gun is at rest, the barrel is pointed down within the slide. But the sights are almost parallel with the top of the slide. As the bullet begins to move forward, the barrel begins to move back and down so by the time the bullet exits, the back of the barrel has dropped enough that the barrel is pointing (hopefully) to the same place as the sights.
Since barrel exit time depends on bullet velocity, the gun will be sighted for only one load (for the GI 1911, that is for the GI load) and any other load will shoot higher or lower. That is the advantage of adjustable sights if one wishes to fire any gun with more than one load.