It can be seen if conditions are right. The eye and brain are pretty wonderful things and sometimes combine their skills to pick it up. I used to do a lot of long range rifle shooting and this required spotting and scoring for the adjacent shooter. Through the spotting scope the flight of the bullet could easily be seen as a sort of wedge of disturbance in the air and I could tell the score even before the markers returned it even out to 1,000 yards. I must admit my shot cloud spotting was a bit easier when my old eyes were a bit younger. Doing some shooting instructing on a local range helps with knowing just where to focus and just where to stand. Lagopus.....
