The purchase and sale of fully automatic weapons in the United States is severely restricted by law. Presumably this includes hand guns. A 9mm semi-automatic was used to kill several kids in at least one school shooting, and bump stocks which are used to make semi-automatic rifles fully automatic are currently legal thanks to a lawsuit by "gun activists".
"Boulder, Colorado: March 22, 2021: 10 dead
Ahmad Al Aliwi Alissa bought a Ruger AR-556 pistol, a semi-automatic weapon with a capacity of up to 30 rounds, six days before the shooting at King Soopers grocery store, police said."
https://www.kcci.com/article/22-mass-shootings-374-dead-where-did-the-guns-come-from/40130537
And, a semiautomatic rifle was used in the Texas school shooting.
A six shooter worked for Wyatt Earp. It, and or my personal preference, a pump shotgun, should be sufficient for home defense, but less practical for mass murder.