HW30s

If they're really close you won't need a scope, the open sights it comes with will do fine. quicker target acquisition too.
Practice a lot first.
To encourage the rats to stay still for a few seconds, use a smear of Nutella 6" up on a vertical surface.
Anything mobile likes bits of bread will be whisked away in a split second.
A thoroughly wetted slice of bread works though!