To all those people who doubted me. Will you please read Jay's answer?

Question

http://answers.yahoo.com/question/index;_ylt=Ai.ojMfYKkrfj2PxWoMXV_3sy6IX?qid=20070716070831AAZzSAk

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Look what I found:
http://www.princeton.edu/~dominic/2003%20-%20Johnson%20et%20al.%20-%20Puzzle%20of%20Human%20Cooperation.pdf

That might explain it.
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Answer 1

Did it occur to you that 'supersonic' refers to
the speed of explosion wave compared to the
speed of the sound in the explosive?

What happens in ambient air is quite
a different story.

Answer 2

Like the other two answers have indicated, you are confusing the speed of sound in ambient air with the speed of explosion. Air molecules simply cannot compress and relax faster than the air density and temperature will allow...which is the speed of sound.

That's why we have the so-called sonic boom whenever an aircraft exceeds the speed of sound. The air molecules in front of the aircraft as it knifes through the ambient air cannot get out of the way fast enough. A standing wave of static air builds up because the molecules pile up but do not otherwise move. If humidity conditions are right, we can actually see this standing wave surrounding an aircraft as it breaks the sound barrier.

Answer 3

Yeah, the shells do detonate, but that does not change the fact that once it does, the speed at which the detonation sound wave travel in air is limited by the speed of sound in the air given the atmospheric conditions.

Another consideration is what you consider to be the time you are measuring? Are you just measuring the time between when you see the flash to when you hear it? How are you measuring it? What is the error in your measurment? No guessing allowed here! You can't rely on just counting yourself because that is too inconsistent.