Viscosity

In the beginning due to gravity pull, the lead shot will be accelerated and hence will move, with increasing velocity for some time When the viscous force balance the gravity pull, then the shot will move with constant velocity. As in the beginning, the velocity of shot is not fully linear with the effective distance covered by the shot.

Radius of drop,
Terminal velocity,
Viscosity of air, poise
Viscous force,
dyne