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“….All supersonic bullets have a sonic-signature, that can be seen with the naked eye, or a scope. The sonic signature is the "disturbance" caused by the bullet traveling super sonic. Likewise when the humidity is high, and especially when the air is more dense(cool); you can see the con-trails.
When you use long match-grade bullets, the bullets tend to wobble, and skid through the air(at least until they go to sleep). The supersonic disturbance compresses the air, and causes the water in the air to "fall out of suspension……"