It sounds like you don't realize how much times have changed since then, and that it might not take any "different circumstances" at all for you to be charged with murder for the exact same thing today depending on the politics of the prosecutor, what area you live in, what color the person you defended yourself against was, what color you are, and/or what political persuasion you are.
The anti-gun sentiment is so incredibly virulent in so many (who often end up being the prosecutors and jurors) that they are looking to stick it to anybody they can who uses a gun in self defense, even when they know the prosecution isn't justified, because they don't care, they just want to see a gun owner sent to prison. The racism is so strong in so many people today that there are some of them who are looking to prosecute and convict anybody they possibly can who is white and defends themselves, or anybody who defends themselves against a minority, and they don't care that the prosecution isn't justified. The political hate is so strong in some that if they have reason to believe you are on the wrong side of the aisle from their beliefs (and you being a gun owner may be all the convincing they need that you are of the "wrong" political persuasion) they are going to try to nail you to a cross even when they know your prosecution is not justified.
If your case happened in today's world they would just as likely try to argue "you should have ran away instead", or "you should have just tackled him and fought with him, he only had a knife", or "you should have shot him in the leg instead", or "but you didn't have to shoot him that second time" and charged you with murder.
Daniel Penny and Kyle Rittenhouse are just a couple of the more famous recent examples where self defense was very clearly justified, and where one or more of the things mentioned earlier were what actually motivated their prosecution, but there are tons of examples out there.
The picture below comes from a case not much different from yours (full video is on youtube). Ma'Khia Bryant was literally in the act of trying to stab another girl to death and the police had to shoot her to prevent the murder that would otherwise be occurring within literally just a split second. There was a
massive uproar from a big part of the general public, and from politicians, and sports and movie stars, etc who said that the shooting was not justified and wanted the police officer charged with murder. They were saying this even after watching the video. One very prominent political organization said Ma'Khia's life was "stolen" from her and that she should be "uplifted, celebrated & honored".
Without that video, the prosecutors in that area likely would have tried to file charges. And the people who were at the scene, who would have been the witnesses at trial, would have lied and said the shooting was not justified, just as you can hear them saying on the video. And it wouldn't be unheard of for a jury from that area to want to convict on something like this regardless of what the evidence really said. The only thing that saved that officer was that it was on video, even though most of them were still wanting to try to find some way to get him nailed to a cross anyway even though it was very clearly justified. As Bavafongoul suggested, having insurance to cover your legal defense if you ever have to defend yourself or someone else is probably a smart thing in this day and age.
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