Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically:
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it's fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that "Eliezer said X is true" unless you use rot13.
The most recent update would suggest that fairly standard shielding charms can stop blunt impact.
"Daphne could hardly see the movement as Susan seemed to hit the corridor wall and then bounce off it like she was a rubber ball and her legs smashed into Jugson's face, it didn't go through the shield but the sixth-year went sprawling backward with the impact"
There appears to be conservation of momentum, but the momentum from typical firearms spread out over your entire body isn't even going to leave a bruise, assuming said charms are up to dealing with something with as much sectional density and velocity as a bullet.
IMO a good model for wizard duels vis a vis muggle innovations and creative thinking is the ritualized warfare practiced in the Americas in pre-Columbian times. Lot's of punches pulled, lots of unstated mutual agreements not to escalate, and a general low-intensity level of aggression that doesn't get too many people killed.
Just not partially motivated by the need to capture opponents for sacrifice?