  We derive two estimates for the deviation of the $N$-particle, hard-spheres
Kac process from the corresponding Boltzmann equation, measured in expected
Wasserstein distance. Particular care is paid to the long-time properties of
our estimates, exploiting the stability properties of the limiting Boltzmann
equation at the level of realisations of the interacting particle system. As a
consequence, we obtain an estimate for the propagation of chaos, uniformly in
time and with polynomial rates, as soon as the initial data has a
$k^\mathrm{th}$ moment, $k>2$. Our approach is similar to Kac's proposal of
relating the long-time behaviour of the particle system to that of the limit
equation. Along the way, we prove a new estimate for the continuity of the
Boltzmann flow measured in Wasserstein distance.
