Wow! Your property looks like a LARGE slice of heaven! Do you fish that lake? What's in it? Walleye, pike, perch? Shoot when you want, fish when you want, How could it get any better. Congratulations on having it all.
I grew up with a Wham_o Deluxe slingshot in my back pocket. I was very good with that thing. But, on my best day, I was nowhere near the lethality of any decent pellet rifle. I doubt there is any add on that will allow a bow shooting balls to hit bird size pests unless they are extremely close...
I wonder how they came up with those numbers? An actual test with the original gun or a replica? 22 shots with a 140 (+/-) gr projectile at 1000 fps sound good for a modern gun.