I was under the understanding that anything with a barrel under the length of 12" was considered a pistol (unless it is singleshot) and cannot have a buttstock, rifles are anything with a barrel of 16" or longer, and shotguns had to have a barrel longer than 18". Of course if you have a class 3 firearms license/taxstamp, or whatever you call them, then you can have a barrel of any length and full auto.

so to the point, on this forum I have seen many people with SBR's they have made with 10.5" barrels and colapsible buttstocks. Is this legal to take a ar-15 rifle and put a realy short barrel on it, or am I just missing something?

If your AR receiver is registered as a PISTOL ... then it is a pistol and cannot legally have a buttstock on it.  If your AR receiver is registered as a rifle it must have a buttstock and at least a 16" barrel.   If your AR receiver is registered as an SBR (Short Barreled Rifle) it must have a Buttstock and can have a barrel less than 16" ...    All depends on how it is  registered with the BATF ...  obviously ... most AR receivers are registered as rifles ..   The SBR costs $200 to register ... Pistols and rifles don't ...

Is the $200 a one time registaration fee or a yearly thing, and can it be done at your local guns shop?

o and why when they sell civilian MP5 and PS90 dont they just have you register it as a SBR, instead they extend the barrel?

Check out the NFA forum ... all the info is there .... it's a 1 time payment ...