EntityFireBullets Callback

[Newbrict]

Hi

I'm trying to overwrite the callback function for EntityFireBullets hook
( [url]http://wiki.garrysmod.com/page/GM/EntityFireBullets[/url] )

Here's what I'm trying:

function GM:EntityFireBullets( ent, data )
	PrintTable( data )
	data.Callback = function( ply, tr, dmg )
		ply:Kill()
		print( "WOAH" )
	end
end

However when I shoot it neither kills nor prints WOAH, what am I doing wrong?

Thanks.

[editline]26th July 2014[/editline]

I wasn't reading the wiki properly "return true to apply changes" thanks guys.