you know the way the purebloods have been portrayed in all the books like they look so far down there noses at muggles that they dont have any clue as to how a typical muggle lives much less how they them selves could move around in the muggle world. So in that case why dont Harry use muggle means to wipe them out!?! Hell take a glock 17 9mm and put a bullet in each of there heads. Now grant you it has been determined that if given a warning a wizard can produce a shield that will block a bullet, but then again wizards and witches dont walk around all the time with a sheild up, it would be to draining on there magic to do so right! So then apparate behind them put a bullet in there heads, knocking off one or two at a time, guerilla tactics you know and then leaving! Or hell better yet get a bolt action rifle with a good scope and a silencer on it and then get on top of a roof in diagon alley and then using his invisiblity cloak to hide him, then when you see either a death eater walk by or if your squemish then wait until they attack then from you hide take out the deatheaters during the fight. A good headshot especially from a silenced and muzzle blast hidden rifle, they would never know what hit them!