Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
The disarming spell would have specifically taken away Voldemort's powerful wand. Even if he were to use a Death Eater's wand after that, it wouldn't be the Elder Wand. Also, the time between disarming & rearming Voldemort could be used to decisively defeat Voldemort.
The important part here is living. An Horcrux, is usually an object. Inanimated and definitely non-living. The killing curse could, most likely, still damage the object because of how powerful it can be, but not really destroy it unless the object in question is fragile.
During his final confrontation with Voldemort, Harry knew that he (Harry) was the Elder Wand's true master. He again cast Expelliarmus, ejecting the wand from Voldemort's hand into his own as the Killing Curse rebounded off his body, fatally striking Voldemort.
His body would die, and he would be back to where he was prior to the first book. You can absolutely "kill" him in a duel, but now that the Death Eaters know that there are ways of creating new bodies and that Voldemort can't be fully killed, it wouldn't delay his return to power like it did the first time.
Harry makes use of two of the Unforgivable Curses in the books. Dueling with Bellatrix Lestrange, he attempts the Cruciatus curse, with limited results; Bellatrix says that he has to really hate someone to make the Unforgivable Curses work properly, righteous indignation isn't enough.
In order to conjure the avada kedavra curse, you have to want to kill your victim. We all know that Voldemort could easily kill a child without an ounce of remorse... but not Snape. Snape didn't want to kill Dumbledore, and this was why the spell was blue instead of the usual green.
Quirrell didn't use the Killing Curse on Harry, because Voldemort said “use the boy” to get the Sorcerer's stone from the Mirror of Erised. If Quirrell had killed Harry right away, he would have lost the chance to get the stone.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
But when Ron and Hermione are about to die by Nagini, Ron casts the killing curse as a last resort and it simply rebounds off Nagini as it was nothing.
Her sacrifice gave Harry the power of love, a protection spell sealed with the blood spilled by her death.
Dumbledore knew that destroying Voldemort's horcruxes was the only way to truly defeat him. He believed that Harry was the one person who was smart, courageous, and perhaps lucky enough to find and eliminate all the horcruxes.
At the beginning of this book, he measures it against Lucius Malfoy's showing he still has it and it is intact. Dumbledore explains to Harry in book 4 that since both wands contained a tail feather from Fawkes the phoenix, the couldn't face each other as they'd refuse to destroy each other pretty much.
We know that they did not use Avada Kedavra. Aveda Kedavra has one effect: it kills. Other curses can be just as lethal.
There is likely a good reason that the Sectumsempra is not an unforgivable curse. It's mostly because Sectumsempra is Snape's personal curse that he created. It is not a widely known or used spell, and it is one that he kept secret — which means it can't be added to the list since no one really knows about it.
Its incantation is Avada Kedavra. The only known counter-spell is sacrificial protection, which uses the magic of love. However, one may dodge the green bolt or block it with a physical barrier.
Yes, if the curse is powerful enough. Hagrid is half-giant, and it is said that giant-blood can “absorb” some of the power in spells. ... For instance, Voldemort's Avada Kedavra can probably kill Hagrid with ease. Yes, but it would require a stronger than average wizard casting it to have a killing effect.
He doesn't trust Snape as Dumbledore does, but he believes that he can detect any disloyalty. Moreover, Voldemort regards Snape as highly intelligent and therefore ' as a true Slytherin ' a person whose top priority is to take care of himself.
He truly believed the Elder Wand had to be passed down through murder, because that is what the legends say. But even if he knew that one only had to be disarmed, Voldemort was still too arrogant to do that. He kills anyone in his way.
Sectumsempra is a curse invented by Professor Severus Snape, during his childhood, when he was known as "The Half-Blood Prince". He created it with the intention of using it against his enemies, and it soon became one of his specialties.
Erroneously believing Snape is the master of the Elder Wand and that Snape's death will make him the master of the Wand, Voldemort kills Snape by having his pet snake Nagini bite him through the neck.
Roughly translated, Expelliarmus – the Disarming Charm – means 'to drive out a weapon' and that's what it does: forces the subject to drop whatever they're holding. Usually that's a wand, which is why it's often seen in duels, and Harry definitely took that to heart, given how much he used it in combat.
Cruciatus Curse ('Crucio')
Harry tried to use this spell himself. The first time was against Bellatrix after she had killed Sirius. His attempt was unsuccessful because, as Bellatrix mockingly explained: 'You need to really want to cause pain – to enjoy it – righteous anger won't hurt me for long…'
McGonagall followed up Harry's action by using the Imperius Curse on Amycus before tying him up with a net, rendering him useless during the Battle of Hogwarts.