And what we predicted has come to pass.

It was far easier to get guns when you were in high school. There were no background checks, none. There were no waiting periods. Lee Harvey Oswald was able to order the rifle used to kill Kennedy by mail. All of that has changed and it is much harder to get guns in 2018 than the period you are talking about.

Other than that, no one I knew owned anything else.
Now, I don't know ANYONE who doesn't own a pistol or assault rifle. I am the same age as the OP. I NEVER had to fear for my life in school. Now kids must live in fear that they will be the next to be shot.
What changed other than "it's easier to obtain a gun built to kill people now" than it was 45 years ago?

You, nothing, just your own assertions.

...on the progression of gun laws in the recent past.

https://www.poynter.org/news/other-massacre-valentines-day-changed-gun-laws

Here's a somewhat relevant quote from the article about fully auto weapons..

In 1934, the National Firearms Act didn't ban machine-guns, but it heavily taxed and regulated them. That regulation stands today. Then Congress passed the Firearm Owners' Protection Act of 1986, which bans the sale of "new" fully automatic weapons, which is why fully automatic guns today are older weapons.

To own a fully automatic weapon, a machine gun, the owner must obtain a federal ATF stamp, undergo an extensive background check and even notify local authorities that they own such a weapon. In the more than four decades that I have been a journalist, I have never covered or heard of a murder in the U.S. in which the shooter fired a registered fully automatic weapon. Mother Jones magazine has cataloged shootings going back to 1982, and not one involved the use of a fully automatic machine gun.

The ones who shot it out with police.

https://en.wikipedia.org/wiki/North_Hollywood_shootout