To sum it up, there is no such thing as an "assault weapon" it a made up media term. But yes there is such thing as an "assault rifle".
The term assault rifle is derived from the German term Sturgewehr which translates into "storm rifle". Its a nickname that Adolf Hitler coined for the StG-44/MP-44. The StG-44 was a revolutionary new rifle. It combined the characteristics of several different gun classes into one package. It featured a detachable magazine like the MP-40 and the BAR, along with a select fire feature that allowed semi-auto (on pull of the trigger only gets you one shot) or full-auto (machine gun). One of the biggest innovations was that it fired a medium powered rifle cartridge (ammo). At the time the rifle cartridges were power rounds like the 7.62x54R (Soviet Union), the .303 British, the .30-06 (United States) 7.7x58 (Japan) and the 7.92x57 (Germany), these were powerful rounds with long range. BUT, they also had strong recoil, if you had this round fireing out of a fully automatic weapon like the German's FG-42 or the BAR the gun would "jitter like a crackhead". So what the Germans did was cut the 7.92x57 down to 7.92x33. What this did was reduce the recoil down to a much more controlable recoil while still retaining the power of a rifle (albeit much weaker than the full-sized, full-powered round).
So then the term assault rifle began being applied to rifles with these characteristics. Pistol grip, select-fire, detachable magazine, and firing a medium powered cartridge. That last point is what makes the difference between and assault rifle and a battle rifle, with the battle rifle fireing the larger rounds I mentioned, examples of battle rifles are the M-14 and the U.S. Navy's Mk.17.
But things in California start to get weird. Precisely because of definitions and a lack of understanding of capabilities. Here, lets use the M-1A as an example.
Kind of looks like grandpa's deer rifle don't it? Anyway, by the criteria we had earlier, by definition this is not an assault rifle. No pistol grip, lacks full-auto capability, and fires a full powered round (7.62x51). By California law this isn't an "assault weapon".
Now let's dress our M-1A up a little bit, change around the furniture. New stock and the like.
Looks a bit different now don't it, almost like a completely different rifle. BUT, the basic workings of the rifle remain the same. It's more like car that's been "pimped out" but has had no engine work and the engine remains in it's factory configuration. Alright so lets break this thing down according to our criteria. Pistol grip? Yes. Detachable magazine? Yes. Select fire? No. Chambered for a medium powered cartridge? No. So therefore this rifle is not an assault rifle in the traditional sense. But California law doesn't see it that way, California law sees this as an "assault weapon" because it features a pistol grip and a detachable magazine. This can be made legal in California with a magazine lock + bullet button modifacation.
For some odd reason California decided to use a different set of characteristics to define "assault weapon". Courtesy of Calguns.(If it comes out hard to read, highlight the text, couldn't get the formatting fixed.)
Category
I
assault weapons
are those specifically named by make and model in
Penal Code §12276 (and echoed in California Code of Regulation
§979.10). These
firearms are assault weapons at even the bare receiver/frame level
– regardless of any particular characteristic
features.
Thus an Uzi receiver would be banned by name, but a similar Group
Industries receiver would be legal (as long as offending Category III
features were not added).
Category
II
assault
weapons consist of the AR15 and AK “series” of
firearms. While AR and AK series were named in the original
Roberti-Roos laws, due to various key court decisions about
“series”
membership it’s
useful to refer to them as their own category, those these guns really
have just fallen back into the Roberti-Roos list once listed by DOJ.
Category
III
assault weapons
are defined by characteristic features listed in PC 12276.1:
RIFLES:
A
semiautomatic centerfire rifle capable of accepting detachable
magazines and any of:
▪ a pistol grip
protruding conspicuously below the weapon’s action
▪ a thumbhole stock
or folding or telescopic stock;
▪ a flash
suppressor, grenade launcher or flare launcher;
▪ a
forward pistol grip.
A
semiautomatic centerfire rifle with overall length of less than 30
inches;
A
semiautomatic centerfire rifle with a fixed magazine holding over 10
rounds.
PISTOLS:
A
semiautomatic pistol capable of accepting detachable magazines and any
of the following:
▪
a threaded barrel;
▪ a second
handgrip;
▪ capacity to accept a detachable magazine at some location
outside the pistol grip;
▪ a shroud attached to, or partially or completely encircles, the barrel allowing
bearer to fire weapon without burning his/her hand, except for a slide enclosing
the barrel;
A
semiautomatic pistol with a fixed magazine having capacity to
accept over 10 rounds.
SHOTGUNS:
A
semiautomatic shotgun having both of the following:
▪ a
folding or telescoping stock;
▪ a pistol
grip protruding conspicuously beneath the action of the weapon,
a thumbhole stock, or a vertical handgrip.
A
semiautomatic shotgun with the ability to accept detachable magazines;
Any
shotgun with a revolving cylinder.
Notice there under the section for rifles, it deviates from the military definition by not requiring full-auto capabilities? California essentially expanded the term "assault rifle" to go beyond the rifle class. So while the military wouldn't consider the dressed up M-1A up there as an assault type weapon, California legislature did for what ever reason.
Also the definition there that California uses for an "assault pistol" (I guess it would be called) you usually see on a sub-machine gun. Maybe California is using the German characteristics for Maschinenpistole (machine pistol). Either way, the military generally only applies the "assault" descriptor to rifles.
So that's what's what. If you pay attention you'll notice a lot of people in the media will call something an "assault rifle" when it isn't. Or they'll just use that big blanket term "assault weapon" which has no real military definition. No real definition PERIOD. I say that because of the fact that "assault weapon" doesn't take into account the gun's functioning. As I've pointed out with the M-1A. We can change around the stock of the rifle, while not touching the working parts and turn it from a simple rifle to "assault weapon" despite the fact that the mechanism, remains the same. The rifle will still use the same magazine, not some 30 rounder, and it remains semi-auto. The core performance has not changed. No more than dropping a 6 CD changer into a car changes the engine's performance. Changing the stock does not make it go from 4 cylinder to V-6.