The focus of this paper is the theoretical prediction of trajectories of solid particles leaving the surface of a propellant grain in a cylindrically-shaped solid rocket motor (SRM). The Lagrangian particle trajectory is modeled while taking into account contributions due to drag, virtual mass, Saffman lift, gravity, and buoyancy forces in a Stokes flow regime. For the conditions associated with a simulated SRM, it is determined that the two dominant forces affecting particle trajectory are the drag and gravitational forces. Thus using a one-way coupling paradigm, the effects of particle size, sidewall injection velocity and location, and particle-to-gas density ratio are examined in the context of an idealized motor. The particle size and sidewall injection velocity are found to have a greater impact on particle trajectory than the density ratio. It is hoped that these findings will be used to assist investigations into particle-mean flow interactions aimed at reducing slag retention and nozzle erosion due to particle impingement.