Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, USA
The impact (terminal) velocity and the mass of the dart (syringe) that hits the animal determine the extent of tissue injury. Modern remote drug delivery systems are equipped with velocity controls. The projector systems that utilize 22-caliber blank charges also offer various power levels (brown, green, yellow and red) as a further mechanism for adjusting the speed and distance the dart is propelled. The goals of this project were to evaluate the factors associated with dart ballistics and develop an equation to aid estimation of the terminal velocity of a given dart over a known distance.
Multiple delivery systems and brands of 22-caliber blank charges were investigated to determine if terminal velocity could be reliably predicted. Projectors investigated included Dist-inject (Dist-inject, Peter Ott AG, Basel, Switzerland, supplied projectors, darts and charges) models 50N, 60N, and 70N, and Pneu-Dart (Pneu-dart, Inc., Williamsport, PA) models 191 and 196. Dist-inject darts studied were 3-ml and 5-ml Easydarts, 3.5-ml Speedydarts, and 5-ml 50-caliber aluminum body darts. Pneu-dart darts tested were 2-ml and 3-ml disposable practice darts. Ramset, CCI, and Palmer charges were studied.
Initial and terminal velocities of the darts were measured using chronographs (chronographs: ProChrono Plus, Competition Electronics, Inc., Rockford, IL and Beta Model, Shooting Chrony, Inc., Mississauga, ON, Canada). Regression analysis of data from 358 trials, which took into account projector model, velocity setting, dart size, dart weight, and charge color, revealed that charge weight was not a statistically significant predictor of terminal velocity (p=0.43). Velocity setting, dart size, dart weight and charge color were predictors of terminal velocity.
An equation for deceleration was derived from dart physical measurements and standard physics laws. The equation took into account initial velocity, dart mass and cross-sectional area, distance traveled, drag, and air density.
[Where V equals instantaneous velocity, Vo equals initial velocity, A is the dart’s frontal area, D is the distance traveled, and m is the dart’s mass. 0.363 is a conversion factor when the drag coefficient is =0.6, air density is =1.21 kg/m3, the negative sign indicates deacceleration of the dart.]
The equation was compared to measured terminal velocity measurements. Based on data from 105 trials, the calculated terminal velocities significantly correlated with measured terminal velocities (r=0.73). Utilization of this formula enables improved accuracy, predicts terminal dart velocity, and helps to reduce unnecessary trauma.