A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Second Amendment was about using a militia to defend the state, AKA, the National Guard. The Second Amendment was not made to enable and facilitate constant mass shootings.
People who make this argument conveniently ignore the next part of the amendment as if it doesn't exist. "...the right of the people to keep and bear Arms,...", which is a clause that clarifies the first part.
Militias at that time were made up of every able bodied man over 17 years old. Private gun ownership was very common and when they were called to the Militia they brought their own guns. The Second Amendment is not about having a government agency own all guns to only be used when a Militia is needed.