  We present three-dimensional simulations of core-collapse supernovae using
the FLASH code that follow the progression of the explosion to the stellar
surface, starting from neutrino-radiation hydrodynamic simulations of the
neutrino-driven phase performed with the CHIMERA code. We consider a
9.6-$M_{\odot}$ zero-metallicity progenitor starting from both 2D and 3D
CHIMERA models, and a 10-$M_{\odot}$ solar-metallicity progenitor starting from
a 2D CHIMERA model, all simulated until shock breakout in 3D while tracking 160
nuclear species. The relative velocity difference between the supernova shock
and the metal-rich Rayleigh-Taylor (R-T) "bullets" determines how the
metal-rich ejecta evolves as it propagates through the density profile of the
progenitor and dictates the final morphology of the explosion. We find maximum
$^{56}\rm{Ni}$ velocities of ${\sim} 1950~\rm{km~s}^{-1}$ and ${\sim}
1750~\rm{km~s}^{-1}$ at shock breakout from 2D and 3D 9.6-$M_{\odot}$ CHIMERA
models, respectively, due to the bullets' ability to penetrate the He/H shell.
When mapping from 2D, we find that the development of higher velocity
structures is suppressed when the 2D CHIMERA model and 3D FLASH model meshes
are aligned. The development of faster growing spherical-bubble structures, as
opposed to the slower growing toroidal structure imposed by axisymmetry, allows
for interaction of the bullets with the shock and seeds further R-T
instabilities at the He/H interface. We see similar effects in the
10-$M_{\odot}$ model, which achieves maximum $^{56}\rm{Ni}$ velocities of
${\sim} 2500~\rm{km~s}^{-1}$ at shock breakout.
