I just saw a Tweet which featured a photograph of an AK-47 and carried the inscription (hashtags omitted): "AK47 stands for Automatic Killer, 47 bullets per pull of the trigger. Much deadlier than an AR15."
Let me explain the problems with this tweet using words of one syllable wherever possible:
(1) "AK" does not mean "Automatic Killer." It means "Automat Kalashnikov," for the type of gun it is (full auto) and the inventor (Mikhail Kalashnikov).
(2) "47" does not mean "47 bullets per pull of the trigger." It stands for 1947, the year it was first made.
(3) The AK-47 available on the American market is no "deadlier" than an AR-15, and not as "deadly" as a semi-automatic .308 or .30-06, both of which can reach out and touch at greater distance with a heftier punch. Back in the last century when I was a deer hunter, I preferred a WWII surplus bolt action .303 Lee-Enfield sniper's rifle to a semi-automatic .308. It made you aim more carefully and didn't waste nearly as many cartridges when you missed.
In the comment meme following the tweet, I read a comment that the "AR" in AR-15 means "Assault Rifle." No, it doesn't. It means "Armalite Rifle," for the company which first made it.
If you want to be 100% absolutely correct in the use of the term "assault rifle," you should confine the description to a rifle capable of full automatic fire, which fires an under-powered rifle cartridge. At the beginning of WWII the Germans equipped their paratroopers with full auto high powered rifles, but the guns kicked so badly that they were near impossible to control. The Germans later improved the full-auto rifle by reducing the cartridge size and power, and the first true assault rifle was born, the Sturmgewehr 44--"sturm" meaning "assault" and "gewehr" meaning rifle. And just to be perfectly clear, "44" does not mean "44 bullets per pull of the trigger," it means 1944, the year the gun was put into production.
Here is a paradoxical fact about the deadly fully-automatic assault rifle: It is actually intended as a life-saving tool as much as it is a life-taking weapon. The main purpose of high-volume small arms fire on the battlefield is not to kill. It is to make the enemy keep his head down so he cannot kill you. The longer your enemy keeps his head down to avoid your full-auto fire, the less time he has to carefully aim and shoot at you. See the Wikipedia article on Suppressive Fire. I saw a documentary a while back which re-enacted a firefight in Iraq. A squad member with a SAW was covering his comrades against fire from a sniper. (A SAW is a Squad Automatic Weapon, usually an M249 light machine gun, which is capable of massive sustained full-auto fire). The soldier with the SAW fired what seemed like thousands of rounds of ammunition keeping the sniper's head down, thereby saving the lives of his fellow squad members. Unfortunately, when his SAW ran out of bullets, the sniper killed him with one shot. In other words, the man armed with the ultra deadly latest model fully automatic assault weapon eventually succumbed to a man armed with a bolt action rifle.
CAVEAT: I don't mean by my title to disparage the intellect of the tweeter by pointing out the tweeter's ignorance. Everyone is ignorant, we're just ignorant on different subjects. The point I am trying to make is that it is best to speak on matters of which one has knowledge and remain silent on matters of which one is ignorant.