U.S. gun legislation is a quagmire of politics. Pretty much anything said on that subject leads straight into IMHO or GD territory, so I’m not going to go there.
I will say that there are some distinctions between hunting and non-hunting weapons that do make a lot of sense. Automatic weapons, defined as a weapon that fires more than one shot for a single pull of the trigger, typically have no use in hunting. Short range weapons like pistols and riot shotguns also aren’t very practical for hunting.
When you start trying to figure out exactly where to draw the line, though, that’s when things stop making a lot of sense. The problem is that folks try to make a distinction between a military style weapon that is designed to kill people, and a hunting weapon which is designed to kill animals. The reality is that anything designed to kill a deer will also kill a man just as easily.
This picture clearly illustrates some of the silliness in U.S. politics and legislation:
The top rifle is clearly a military weapon, and is therefore an “assault weapon” and should be illegal. The bottom rifle is a hunting rifle, and should be legal. The catch? They are the same weapon. It’s just that one has a military style plastic stock on it and the other has a traditional smooth wooden stock on it.
In order to be useful for hunting, a weapon has to be reasonably long range (typically accurate to 100 yards or more) and it has to do enough damage to reliably kill an animal. There are obviously different types of hunting weapons. You don’t need a large caliber round against a squirrel. If you shot a squirrel with a typical round used against deer, there wouldn’t be much left of the squirrel, and that kinda ruins the point of hunting the squirrel if you intend on eating it. On the other hand, a round designed to kill a squirrel will probably just wound a deer without killing it, which is just cruel. So many states have laws about what caliber of weapon you can use against certain types of game. The point is though that the size of the round doesn’t determine whether the weapon is designed for hunting or some other purpose. A hunting weapon can be anything from a varmint gun to an elephant gun.
The U.S. does not operate under a single set of rules. Each state has its own rules. So exactly how things are defined in the U.S. generally results in 50 different answers simultaneously. My state (Pennsylvania) classifies weapons as handguns, rifles and shotguns (basically, hunting weapons), “offensive weapons” (those which are required to be registered under the National Firearms Act, like automatic weapons and short barreled shotguns), and antique weapons (which includes modern replicas, as long as they follow the same design). Handguns require paperwork. Hunting weapons are basically not restricted, nor are antique weapons. “Offensive weapons” are more tightly regulated.
Other states will vary significantly.
I have no idea what the legal distinctions are in Europe. Heck, I can’t even keep up with all of the different states over here. I know my state and the surrounding states, but I’d have to look up the laws for anything else.