well the shorter answer is yes. The movie version of the gun is a SBR. If it is a rifle the barrel must be 16 inchs long. If it is a pistol the barrel length does not apply (though i have heard that the barrel lenth has to be under 16 inchs). If you look at the MP5 look alike that ar for sale to the public, you will notice the long ass barrel they all have. Most websites list them as "fake supressors." Simply put. If your gun has a stock (or anything that can be quickly converted or used as one) the barrel muct be over 16in or registered as a SBR. I still suck at posting pics but here goes...
Rifle
notice the long barrel.
Now for the pistol version of the same weapon the barrel is much shorter but there is no stock. Those are really the only 2 differences.
there are a few other measurements that Qualify a gun as a pistol vs a rifle but most are based on lenth and such. The 2 big ones are stock vs no stock and barrel length.
Other things to note..... DO NOT take your rifle or one you bought and remove the stock, put in a short barrel, and call it a pistol. If a gun starts its life as a rifle (registered as such when assembled at factory or bought) then it is ALWAYS a rifle. And do not even get me started on vertical forend grips.......
If this is still confussing to you feel free to PM or email me or post for clariication.
jimmy