Question about converting an AR into a different caliber?

Different guns have different purposes and this is why many of us, ultimately own several. It would be wisest and least expensive to be content with owning an AR-15, for example which shoots 556 and 223, and owning an inexpensive rifle which shoots a 22. I saw a very nice 22 at a very good price in a pawnshop this week. It doesn't take very long to clean two guns.