Autofill columns and rows simultaneously

I'm wondering if there is a way to autofill colums and rows simultaneously.

Right Now I have a formula in B3. I want to autofill it over to AD and down to row 40. The following code works:

y = Range(Cells(3, 2), Cells(3, 30)).AddressLocal(0, 0)

ThisWorkbook.Sheets(1).Cells(3, 2).AutoFill Destination:=Range(y), Type:=xlFillDefault

but if i change y to:

y = Range(Cells(3, 2), Cells(40, 30)).AddressLocal(0, 0)

the autofill doesnt work. is there a way to do this?

Thanks,
Joe