It was the bolded part, but you're in denial.
https://simple.wikipedia.org/wiki/M16_rifle
The M16 uses the 5.56mm NATO (.223) caliber cartridge,
with a muzzle velocity (the speed of bullet leaving the rifle) of over 900 meters per second (over 3,000 feet per second), and has a maximum effective range of 550 meters, with a rate of fire (how fast the gun shoots) of approximately 800 rounds per minute.
If you know any rock throwers moving rocks that fast, pro baseball teams would love to talk to them.
A rifle against a rock is not "self defense".
It seems the most basic of concepts are beyond your comprehension. If one amendment can be changed by executive order, then any or ALL of the amendments can be changed the same way.