Closest ear witnesses:
1,Harold Norman. 5th floor, right beneath SE corner 6th floor. Heard 3 shots, all 3 fired in a span of approx. 5 secs, given Normans interviews replicating the sequence with his "boom clack clack" description.
2.Amos Euins: Only approximately 30 yds away on the elm st corner looking up at the SE 6th story window. Saw a rifle and man holding it. Heard FOUR shots fired.
3.Majority of other earwitness heard 3 shots, 1st shot, then a few seconds, then 2 shots back to back, and in Lee Bowers example, the last 2 shots within about 1 sec apart, given his rapping his hand on the desk to replicate the timing (filmed interview with Mark Lane).
Conclusion: Low probability all shots were fired by an MC rifle, if these witness observation are correct.