dean wrote:
Ok I know i can drill a whole load of little holes in a circle and then
knock it out, but is there such a thing as a 4" drill bit that will do
this more easily?

Thanks!

DeanB

Certainly is. It's called a core drill. Available in wet versions or dry
versions. The cleanest, most efficient, and easiest drilling is a wet
diamond bit. Problem is, the cost hundreds of dollars, and require
either a special drill that directs water into the center, or a water
swivel attachment for a conventional drill.
Dry core bits work much slower, and cost a lot less.
Do you need a very clean & accurate hole? If not, save your money &
punch it out with a series of 3/8" holes & a chisel.