Also, skipping from the musket to the modern breech-loading magazine rifle:
you have the deer rifle. The deer rifle is there to put a hard metal slug into a deer. The slug stays intact. The shooter is about a kilometer from the deer, which is too far away to smell or see or hear. And he shoots, and the ammo is powerful enough to be accurate to within a few centimeters from a kilometer away, and throw a bullet halfway into a deer, and blow out its organs. One shot, one kill. One does not spray and pray at a deer. You aim each shot carefully, and often use a small telescope on the rifle.
Around this platform, armies built the battle rifle. The battle rifle is a deer rifle with more ammo storage. Usually troops just used "iron sights" without a scope to aim. Most battle rifles were "bolt-action" like the deer rifle, though a few were "semi-automatic" meaning the rifle reloaded itself.
People who fought commies noticed, first the Nazis and then US in Korea, that commies didn't really sit a kilometer away and trade carefully aimed shots at you. Commies like to run up on you in big groups, and fire burp guns loaded with weaker pistol ammo, and throw grenades. Commies are liable to be a couple hundred meters away before you know they're attacking you. And if you just sit and shoot at them with battle rifles, you're in trouble, because Commies shoot their weaker burp guns faster and more often than you do. Then your guys iwth the battle rifles either die, or, get rescued by incredibly expensive and precious tanks and aircraft. It costs a lot to do that, so, generals thought, it would be a lot better if the average rifleman could just dispose of commies himself.
So they invented the assault rifle. The assault rifle is weaker than a deer rifle. It can't shoot a deer with one shot from a kilometer away. It's stronger than a burp gun, though, and it's as fast as a burp gun. It holds more ammo. It's for shooting down Commies running at you with rapid-fire pistols and grenades before they can get into range to be really accurate, and often enough, that they give up and stay away. NATO pretends that soldiers don't need to shoot farther than 400m, really, because NATO pretends they can always get back in their armored truck and engage enemies further off iwth the machine gun, which is a fully-automatic deer rifle. The guys on the mountaintops of Afghanistan or stranded in Mogadishu had another story, but, those bastards don't buy rifles for NATO.
What it comes down to, politically, is that I am instructed I don't need a wicked mean assault rifle like the AR15 -- I can make do with a Springfield M1903, or a Gewehr 98k, or a Lee-Enfield Mark 3 military collectible, which is not an "assault weapon" even if it could knock the lungs out of a deer at a kilometer. That's a 'safer' gun.