  We report on the computation of the scaling of QCD observables with the
number of colours, $N_c$. For this, we use dynamical configurations with four
active flavours, $N_f=4$, and values of $N_c=3-6$. We study the meson masses
and decay constants, and compute the leading and subleading contributions to
the Low Energy Constants (LECs) of the chiral Lagrangian. We also explore $\pi
\pi$ scattering in the $I=2$ channel, and compute the $K \to \pi $ weak decay
matrix elements. We comment on the relation of the latter to $K \to \pi\pi$
processes and the $\Delta I=1/2$ rule.
