I've a wrist rocket for squirrel control. Regardless of the projectile velocity, fumbling around with a wrist rocket and a sack of ball bearings is no way to confront a criminal. You're dead before you can get the thing loaded.
I have a soft-air pellet gun for that. It's battery-powered and full-auto, about 5 rounds a second and about 175 fps. I'm looking to chase them off, not to kill them, because then I'd have to dispose of the carcass. And frankly, if I could negotiate with the wee beasties, I'd be happy to give them the run of the yard if they'd just stop trying to gnaw their way into my attic.
I'm close enough to neighbors that a firearm, bow or crossbow would get me in legal trouble; I'm not sure about a slingshot. My rodent harassment device, as I've dubbed it, is made of clear plastic; I'm not looking for verisimilitude, and I'm not looking for the hassle of a neighbor or passer-by who thinks I'm stalking fuzzy-tailed tree rats with an actual firearm.
I also have a single-shot soft air pistol, a replica of a Walther P22, that's more accurate with a higher muzzle velocity. But when the object is rodent harassment, it's more effective to pepper the little SOB with dozens of shots on or near his furry little butt than a few better-placed ones.
I think my long-term solution to the squirrel problem is going to be to put an owl box high in one of my trees, and let the rich pageant of life run its course. It seems more practical than my other idea, which was to adopt a pet bobcat or ocelot.