  We present a model of gamma-ray emission from core-collapse supernovae
originating from the explosions of massive young stars. The fast forward shock
of the supernova remnant (SNR) can accelerate particles by diffusive shock
acceleration (DSA) in a cavern blown by a strong, pre-supernova stellar wind.
As a fundamental part of nonlinear DSA, some fraction of the accelerated
particles escape the shock and interact with a surrounding massive dense shell
producing hard photon emission. To calculate this emission, we have developed a
new Monte Carlo technique for propagating the cosmic rays (CRs) produced by the
forward shock of the SNR, into the dense, external material. This technique is
incorporated in a hydrodynamic model of an evolving SNR which includes the
nonlinear feedback of CRs on the SNR evolution, the production of escaping CRs
along with those that remain trapped within the remnant, and the broad-band
emission of radiation from trapped and escaping CRs. While our combined
CR-hydro-escape model is quite general and applies to both core collapse and
thermonuclear supernovae, the parameters we choose for our discussion here are
more typical of SNRs from very massive stars whose emission spectra differ
somewhat from those produced by lower mass progenitors directly interacting
with a molecular cloud.
