I've just got my 850 adjusted to 900fps average (chrono'd) and see pellets in flight frequently with my scope on 9X. I've been pellet testing the past week and have gone through 14 types of pellets and can see them all in flight. Shooting at white paper targets helps as well as the sun to your back, but isn't necessary. The pellets that fly straight and fastest are the toughest for me to see. Some of the heavier and wadcutter pellets spiral violently and you can trace them to impact. As mentioned before, the Crosmans are brighter and you can see the sun reflect off the back of the base. The other pellets are either black or have a conical inside and just appear as black spots in flight.
Pretty cool.