Harry Potter: Why Don't Death Eaters Just Spam Avada Kedavra in Battles?

Thanks to Barty Crouch Jr. who was pretending to be Alastor Moody at the time, we learned the three Unforgivable Curses together with Harry Potter and his friends. The Imperius Curse controls the minds; the Cruciatus Curse inflicts insufferable pain; and finally, the Killing Curse, Avada Kedavra, drops any opponent dead on the spot.

Now, for what it’s worth, we don’t really encounter Avada Kedavra all that often over the course of the Harry Potter series. It’s talked about a lot thanks to Lord Voldemort actively using it, but a rare Death Eater even attempts to cast the Killing Curse even in the heat of a deadly battle. This doesn’t make any sense now, does it?

Avada Kedavra can’t be blocked or deflected, and it kills immediately, so it sounds like the perfect curse for the Death Eaters whose objective is often to take out as many opponents as possible by any means necessary. If we look at the situation from this angle, it almost seems like they are simply self-sabotaging, those guys.

This is not the case, of course. Let’s see what Professor Crouch had to say about the Killing Curse and its specifications back in Harry Potter and the Goblet of Fire.

“Avada Kedavra's a curse that needs a powerful bit of magic behind it – you could all get your wands out now and point them at me and say the words, and I doubt I'd get so much as a nose-bleed,” the disguised Death Eater told the Hogwarts students.

The Killing Curse is not a spell you could effortlessly throw around in a battle unless you’re specifically trained to do that. It requires a lot of concentration and raw magical power, and in the heat of a battle, you don’t want to spend extra strength and focus to drop down a single enemy while being surrounded by many others.

Some Death Eaters were likely too weak to even be able to cast the Killing Curse; others were too inexperienced with it to risk diverting their attention to cast it. The risk-to-reward ratio was too low with Avada Kedavra in a real battle, that’s it.

There were only two wizards that we know of that were using the Killing Curse effortlessly even when engaged with multiple opponents at once: Lord Voldemort and Bellatrix Lestrange. Both of them were utterly insane and sadistic wizarding powerhouses, so they could Avada Kedavra their way through most obstacles.