I have no idea what point you're trying to make. How can one hear something 10,000 miles away?
A gunshot can be heard (by people who can hear) 10,000 miles away from where I am right now and from wherever you are right now.
A gun can be fired most any place the world over, legally or not, and wherever one is fired, people nearby will be able to hear it.
I was trying to make two points:
1) The question "How far away can a gunshot be heard?" can be answered by any distance measurable on the earth.
2) Because of the first point, I don't think "from" should be deleted from Tufguy's sentence. We could front it, though, if you like:
From how far away can a gunshot be heard?