Bart shoots the animal he previously hit, knocking it out once and for all.
Sean kills another animal with a shot to the vitals.
Only one rat-dog thing left running away.

Neither Sean or Richard can see the riverboat too much. It is very much far away. The steam from its chimney rises high into the air. It is moving at a minimal pace, perhaps 1 or 2 yards a second. It's too hard to make out much more detail than that.

It is now about over ten minutes away (600 yards?) from the power plant.

(OC: if you want a Range penalty, consider it -15, extreme range. Note that the riverboat itself is SM +10.)