Like I said, I have the S1K .177 and S1K .22 "Black Shadow" and if I am not mistaken, it has the same power plant as the Gamo 440 .177 and .22. But for someone who would know. It is CharlieDaTuna, cause he has worked on them all.
I have used my S1K for squirrels and it gets the job done at 30 to 40 yards for sure. Anything past that, I would use the 1250. Not that I could not put a hole in a squirrel at 50 yards but it would be inhumane. "Not a Clean Kill". Or you would have to be a dang good shot to hit the squirrel in a vital place ever time at that distance
All of my Kills have been around 40 yards or closer with the S1K.
Now, I want to say this. I do not eat squirrels. I do not kill them for slaughter. There is a man who is very poor that lives a mile from me and he loves squirrel stew. He gets all my catch of squirrels. He skins them and dresses them out right on his back porch.
So there ya go..
Ask the expert on the power plants, velocities etc.. Dat would be CharlieDaTuna
Gene