While it is accepted that BC is a function of mass, diameter and drag coefficient there are many, many factors that need to be taken into account. The type of barrel, diameter, riffling, interior roughness value, temperature, humidity, altitude and on and on and on. I've had two TX200 MkIII air rifles. The first being stolen in Phoenix. Each rifle had a slightly different BC using the .22 H&N Baracuda Green pellets. Each rifle was tested under the same environmental conditions at the same facility. The first TX had a BC of 0.0135 while the second had a BC of 0.0137. This slight change did not effect the POI, however, it did effect retained energy. 0.0135 = 90% at 6yds, 80% at 13yds, 70% at 20yds, and 60% at 29yds. 0.0137 = 90% at 6yds, 80% at 13yds, 70% at 21yds, and 60% at 30yds.