Most of my .25 squirrel hunting was with a .25 Crow magnum springer back in the late 80s, or early 90s. It was a good killer, but not much past 30 yards. In the last ten years, I went PCPs , most of my hunting has been .22. I like mine smoking 950 fps with 18 grain or 16 grain. Longest shot on a fox squirrel was 83 yards, was dead before it hit the ground. My kills are usually clean, if I keep all my shots under 60 yards & use higher fps. Sometimes when I get a new rifle, they are in the high 800s or very low 900s, I don't know why, but I seem to lose a few squirrels, not a lot , but one is too many. Then I jack them up to 950 + and no loses. I have a Royale 400 that shoots @ 1000 fps 18 grain jsb. With that rifle I have taken over 250 tree squirrels & I might be able to count on one hand the shot squirrels that got away . The small accuracy loss & I mean small, at this higher fps is worth it to me to have more humane kills. I am not sure a .25 would make them any deader. I know people take a lot of squirrels at 800 fps, I used to take some with my blue streak when I was a kid. If you are a superior shot and can put it through the eyeball every time, 600 fps would be enough.