I dont know the shot count buddy, but if you know both the ME and capacity of the air cylinder, then CGP has a very good shot count Calculator in it
For close range ferrals and rodents, how about something light and robust. If you were thinking of smk, then the xs19 is a little long and probably heavy for you, deadly springer though mines runnung untuned at 10.5ft/lbs.
The QB's are quite light (not sure of ME though) or even a Ratty / King ratty I would also reccomend a lightish pellet and as your shooting close in, a flathead/wadcutter type.
Less chance of it comming back at you.