What is the influence of sand grain shapes on an hourglass accuracy, and how does it affect the jamming probability? We study such a question using numerical simulation and our recently introduced spheropolyhedral particles. Spheropolyhedra constitute a very rich class of shapes that naturally generalize the traditional spheres used in the Distinct Element Model. Our experiment consists in pouring particles into a container pierced with a circular opening, and to note whether they flow or jam. By repeating this experiment, one can evaluate the jamming probability of a given granular assembly. We show here that intuition is misleading: while the jamming probability is clearly dependent on friction, it does not show a dependence on particle sharpness.