Question on rifles in B42

I was clearing out riverside, and I was noting that zombies ragdolled a lot more often when I shot them with a pistol than with a rifle. Every other shot with a pistol would ragdoll a zombie, but I usually needed to land three shots with a rifle to ragdoll. Is this a symptom of having low levels in aiming (this character only had aiming level one)? It was hard to keep track of individual zombies, so I wasn't sure if the rifle was actually killing zombies faster.