  The angle of repose for the flow of granular materials in a half-filled
rotating drum is studied by means of experiments and computer simulations.
Particles of different material properties are used to investigate the effects
of the end caps on the angle of repose. By fitting the numerical results to an
exponentially decaying function, we are able to calculate the characteristic
range, $\zeta$, of the influence of the wall. We found that $\zeta$ scales with
the drum radius but does not depend on either the density or the gravitational
constant. For increasing particle diameter, finite size effects are visible.
