An assault rifle by its true definition is a select fire weapon capable of full auto function. For example, an M-16 can, with one trigger pull, fire either single-shot, multiple shot or full-auto. An AR-15 (which looks the same cosmetically) can only fire one bullet each time the trigger is pulled (semi-auto).
In the US, to be able to own assault rifles legally, they have to be NFA licensed weapons, and the owner must purchase the appropriate tax stamp from the BATFE. The rifle will have to be purchased/transferred through a Class III dealer.
In 1994, gun control advocates came up with the term "civilian assault rifle", largely as a confusion tactic, as the general public wasn't expected to know the difference between those and a full auto military rifle. The BATFE determined that any detachable magazine rifle with two or more of the following features was was considered a "civilian assault weapon":
As the ban was based solely on cosmetic features, it was easy enough to make compliant designs, simply by removing, or having only one of these features. For example, if the rifle had a pronounced pistol grip, and none of the other features, it wasn't considered a 'civilian assault rifle', because it only had a single feature. Eventually, the BATFE determined that muzzle brakes were acceptable, so long as they were permanently attached.
After the sunset of the ban in 2004, the states of New Jersey, New York, Connecticut, Massachusetts, and Cook County, Illinois have kept this ban in their own law books.
California has had such a ban since before the federal ban, and theirs is a much more sweeping ban. Unlike other AWB states, where you can still have a single feature rifle or import a pre-ban rifle, all such firearms had to be registered with the state in 2000, and could not transferred to anyone else within the state.
With the current California laws, you either have to have owned your weapon prior to the 2000 registration, or else you have two options - there's a fixed magazine rifle, in which case, it doesn't meet the definition of a 'civilian assault weapon' (which must have a detachable magazine), and you're allowed all the features you want - or you must have a featureless rifle - no pistol grip or thumbhole stock, no collapsing buttstock, no flash suppressor - California law also bans forward grips.
On top of all that, you also have to ensure that you have an off-list lower receiver. If you wanted to make a California complaint AR-type rifle, a Colt lower would be illegal, as it's listed in the California DOJ ban list, but a Daniels' Defense lower would be perfectly legal, as they're not (yet) listed by the California DOJ.
One cannot legally purchase an assault rifle anywhere in the UK. In the UK one may buy certain firearms, notably shotguns, but there are strict conditions attached to ownership.
A true "assault rifle" that can be transferred legally will run you 10000 and up.
No such weapon, so no. However, there there is a M16A4. It is possible, but, highly unlikely that an individual can buy one.
Have never heard of an underwater assault rifle. In the US, you must be 18 to buy a rifle, and 21 to buy a fully automatic rifle.
18 to buy a rifle or shotgun, 21 to buy a handgun or assault rifle.
No.
If able to be legally transferred, multiple thousands.
Assault rifle is legally defined as a rifle having a detachable magazine, of intermediate rifle caliber(medium power) and selective fire. (machine gun). the Media has corrupted it to be anything.... AR=automatic rifle.
You can buy a semi automatic Title I rifle at 18. To purchase a true, select fire (auto or burst) NFA tax stamped assault rifle, you must be 21.
You will need to define assault rifle, and where you live. A TRUE assault rifle is a machine gun, and transfers of them are tightly regulated by the Federal government. What most people CALL an assault rifle is nothing but a semi-automatic rifle, and in most of the US, does not require a license to possess.
A TRUE Assault Rifle is fully automatic. Federal law requires you be 21 to buy one of those in ANY state. However, what people may CALL an assault rifle (such as a semi-auto AK47) can be purchased at 18.
Not legally.