The efficiency of the Condor shot was only about 3%, IIRC.... Maybe that was because only a small percentage of the air was moving fast enough to push the pellet over 1700 fps.... After all, the RMS velocity is just a point in the Maxwell Speed Distribution of velocities in a gas at a given temperature.... and in fact a small percentage of molecules are moving more than twice as fast as the RMS value....
Perhaps with enough data we would see not a hard and fast "limit" but just a very rapid tapering off of the possible velocity as fewer and fewer air moelcules are moving fast enough to provide additional acceleration.... Just a thought....
