Airmaks Katran

Clean it when you see accuracy diminishing beyond what you need/want.

Too open of a question for a specific answer. Need for cleaning can be very dependent on brand of pellet you are using, and your personal accuracy requirements (for example 100 yard bullseye competition vs 50 yard 'minute of squirrel.). Some pellet brands are softer than others (like JSB vs H&N) and will lead up a barrel faster. And some barrels like to be leaded up somewhat for most accuracy.