Harold Norman, the closest ear witness right underneath the SE 6th floor SN, heard the 3 shots fired in approximately 4 seconds or less if you measure his several recorded video interviews.
also Norman stated he heard the 1st shot fired, saw JFK "slump' and only AFTER that, did Norman hear 2 more shots fired. So that 1st shot that Nnorman heard, must be 223, because any earlier, JFK has NOT slumped yet.
so 3 shots in 4.8 seconds, of which the SECOND shot must have missed around Z frame 290, followed in about 1 sec by Z 313 head shot.
This rules out a MC rifle firing all 3 shots. Its possible to have fired 2 shots spread apart by 3 seconds but surely improbable to have fired a 3rd shot 1 second after the missed 2nd shot.
This compares well also with James Tague, who thought it was the 2nd or 3rd shot that struck the curb near his position at the tunnel of the Triple overpass, or a fragment of such shot, that may have caused a superficial cut wound on his face.
Lee Bowers, the tower operator behind the stockade GK fence, who saw something like a flash of light that caught his eye, replicated his memory of the shots as spaced also within 3 or 4 seconds just like Harold Norman. Bowers raps his hand on the desk in about 1 sec spacing between 2nd and 3rd shot.