How about a machine gun then? A grenade launcher? An Anti-Tank Guided Weapon? A Tank? A Howitzer? Where do you draw the line on this so called "Fundamental right"?
There is nothing in the second amendment that says you need more than a shotgun or Air Rifle. Both are more accurate and deadly than anything available in the late 18th century.
Those are all weapons considered to be dangerous and unusual, their possession is not entitled to Constitutional protections.
Handguns are considered to be in common use, their possession is entitled to Constitutional protections.
As such citizens are not required to justify possessing handguns; citizens are not required to justify exercising the right to self-defense.
And until such time as the Supreme Court makes a determination as to the status of AR 15s – in common use or dangerous and unusual – citizens are not required to justify possessing an AR 15, or using them pursuant to the right to self-defense.