If you intend to subdue, not kill, in real life, you use a taser/pepper spray/whatever, not a gun.
Ever heard of a "warning shot"? ;-)
Seriously, though, you're not noticing that you're confused, here. For at least a week, a whole bunch of people here and on Fanfiction were going, "Wtf? Why is Quirrel holding the idiot ball?", precisely because it would be idiotic to kill the auror, unless Q's plan is considerably more complex than the story lets on.
In a way, we were suffering from Harry's Intent To Kill bias, and thereby overlooking the non-lethal strategic potential of having a spell that must be dodged, and thus can be used to put an opponent on the psychological defensive.
Bahry took all the non-lethal damage Q could dish out, and spat at the offered terms - but he took the AK threat seriously, and might have negotiated in preference to having to dodge a second AK -- especially if Q told him the first was just a warning shot.
It was clearly within Quirrelmort's power to subdue Bahry without escalating to the use of the killing curse. He wasn't even exerting himself during the duel; if he needed to position Bahry for some reason, he could simply have started to pursue and maneuver. Bahry was clearly already on the psychological defensive, and was being forced to dodge his attacks, so using the killing curse is redundant for those purposes. Bahry's own monologue notes that his magic was almost completely exhausted. He wouldn't have been able to hold out much longer anyway.
If Quir...
- This thread has run its course. You will find newer threads in the discussion section.
Another discussion thread - the fourth - has reached the (arbitrary?) 500 comments threshold, so it's time for a new thread for Eliezer Yudkowsky's widely-praised Harry Potter fanfic.
Most of the paratext and fan-made resources are listed on Mr. LessWrong's author page. There is also AdeleneDawner's collection of most of the previously-published Author's Notes.
Older threads: one, two, three, four. By tag.
Newer threads are in the Discussion section, starting from Part 6.
Spoiler policy as suggested by Unnamed and approved by Eliezer, me, and at least three other upmodders:
It would also be quite sensible and welcome to continue the practice of declaring at the top of your post which chapters you are about to discuss, especially for newly-published ones, so that people who haven't yet seen them can stop reading in time.