  In earlier papers, techniques have been described using optical chronographs
to determine free flight drag coefficients with an accuracy of 1-2%,
accomplished by measuring near and far velocities of projectiles in flight over
a known distance. Until recently, Doppler radar has been prohibitively
expensive for many users. This paper reports results of exploring potential
applications and accuracy using a recently available, inexpensive (< $600 US)
amateur Doppler radar system to determine drag coefficients for projectiles of
various sizes (4.4 mm to 9 mm diameter) and speeds (M0.3 to M3.0). In many
cases, drag coefficients can be determined with an accuracy of 1% or better if
signal-to-noise ratio is sufficient and projectiles vary little between trials.
It is also straightforward to design experiments for determining drag over a
wide range of velocities. Experimental approaches and limitations are
described. Overall, the amateur radar system shows greater accuracy, ease of
use, and simplicity compared with optical chronographs. Doppler radar has
advantages of working well with less accurate projectiles without putting
equipment at risk of projectile impact downrange. The system can also detect
phenomena that optical chronographs cannot, such as projectile instability
resulting in tumbling in flight. This technology may be useful in introductory
physics labs, aerodynamics labs, and for accurately determining drag and
ballistic coefficients of projectiles used in military, law enforcement, and
sporting applications. The most significant limitations are reduced
signal-to-noise with smaller projectiles (< 5 mm diameter) and inability to
detect projectiles more than 100 m down range.
