Also OT, but.....
Friend of mine had a gang of crows begin nesting in a big backyard tree. He told me that he swiped a slingshot (WhamO Wrist Rocket IIRC) from one of his kids, hauled that and a dishpan filled with ice cubes out on his back deck and launched away every time he saw a crow.
He said that it didn't affect any other birds and he left the mama crow & fledglings alone until they finally left, but besides that he hasn't even seen a crow within a half-mile of his place for the last three years.
Don't know if grackels are smart enough to figure out the deal as well as those crows did, but having ice cubes go by pretty quick should at least get their attention....and it won't even leave blood or bullet holes.
Nice idea! I’ve a couple of grandsons who need practice...