What is a safe shooting distance for each caliber?

Safe distance is more about backstop than caliber, but as a rule, .177 pellets can be dangerous out to 400+ yards, .22 to 500+ yards, and big-bore airguns to half a mile or more.

Plan your shooting so that any missed shot terminates in a safe backstop, not in air. Indoor and backyard ranges of 10 yards are routine for .177 and .22; for .25 and up, larger spaces and heavier traps are needed. Big-bore practice belongs at a dedicated range.