It is extremely hard to purchase an automatic rifle in America. Plus they are cost prohibitive for all but the rich. No automatic rifle has been used in the commission of a crime since the prohibition era when they were virtually outlawed. Not one.
Plus you aren't as effective as you would think with an automatic rifle. It will never be one bullet per victim unless you have everyone bunched together in a group. That's why in the military they fire short burst of about 3 or 4 rounds. Anything else is a wasted of ammunition. TV and movies lie to you. They show guys firing non-stop and taking out everyone because it has more action and shows better in movies. But that is not real life, not even close. Movies and TV don't take into consideration the recoil of the weapon and reacquiring your target after the recoil of each bullet.
Now if you are talking about semi-automatic rifles (which many on the left don't realize is not the same thing as an automatic) then you are reducing your fire capacity. A semi-automatic fires one bullet per trigger pull. The most widely owned semi-automatic rifle is the AR-15 which fires a .223 caliber round or a NATO 5.56x45mm round. They are roughly the same bullet. That round is significantly smaller than most hunting rounds which is why many people say you can't go hunting with an AR-15. Well, you can and many people do but typically for smaller game than deer. The NATO 5.56x45mm round was introduced to the world's military with one purpose in mind. To reduce the number of casualties in war. Higher caliber ammo is more deadly. Ammo is measured in inches or millimeters diameter. A .223 round is .223 of an inch in diameter or .003 of an inch larger than a regular old .22 rifle, like the rifle my dad bought me when I was 14.
After far as knives go there is a 22 foot rule that applies. If you have a holstered firearm that is easily accessible (i.e. not concealed) and a guy comes at you with a knife then they have to be at a minimum of 22 feet away in order for you to draw your firearm, aim and shoot. If the guy is closer, which nearly 100% of the time he is, then your firearm is just decoration.
I saw a video a few years ago on YouTube of a guy in a foreign country take out about 6 or 7 armed police officers with a knife. One advantage a knife has over a firearm is that the knife is always dangerous whereas a firearm is only dangerous when firearm is loaded, a bullet is chambered and the trigger is pulled.