25 grain .17 cal Remington hollow points.
They were for my Model 700 Remington bolt action which was the answer to the question…”How do you turn a prairie dog inside out?” 
Works good on fox too if your pelt hunting. There was seldom an exit wound as the hollow points pretty much self destruct in side a fox. Entrance wound wasn’t to big either.
If I recall, it’s a .222 case necked down to .17 cal. Had to watch the reloads as too much speed wiped the barrel or keyholed the bullets. 