That is utter fucking nonsense. What do you think can be stopped faster, a dude running around with a military-style automatic assault rifle or a dude with a bolt-action manual hunting rifle with a magazine he has to reload every ten rounds? What do you think is easier to get in a society that bans the former but allows the latter under sensible legislative control? And if an assailant did use the latter to attack, what would happen?
Spoiler alert: they are stopped. Quickly. We know this to be true.