Pistols can only kill very soft-bodied critters like worms, everything else is resilient enough to not be hurt.
The only other animals they endanger are dumb hermits, as they'll sometimes incorporate hermits into their tunnel supports if the hermits keep coming inside. Pistol shrimp line their tunnels with bits of rubble to help keep them up, and they'll use a hermit that isn't smart enough to stay away. Hermits are usually strong enough to drag themselves out, but sometimes they get stuck.