Depends on where you strike it,  i've dumped 20-30 30mm into one before it went to pieces , course I was working the engines after killing the gun positions (wanted to extend the pleasure  

 ) , in 4xcannon bird i find  top/bottom attacks require 50 rounds at least or as much as 100 to explode it, from 6 position working on one wing 30-50 cannon does great.  I personally feel that its a tough bird ,,,,but no competition for any plane intend on killing it , seen zeros kill em without much problem.