Originally Posted by tacticalcity
From what I remember reading it is because the magazine is not in the grip, and on a pistol a detachable magazine has to be inserted into the grip to be legal here. Since this state defines a fixed magazine as one that requires a tool to remove, installing a bullet button means it no longer is capable of accepting a detachable magazine outside of the grip and thus is legal...or so the current popular interpretation of the law goes.
If I am wrong please correct me. I am by no means an expert on pistol ARs.
There is a flow chart showing what is and is not allowed on pistol ARs somewhere here. Do a search for it and you will learn all you need to know. Discussing it here is kind of hijacking the thread, since people want to see pictures here...and learn about the law there. Not trying to be rude, just trying to avoid being flamed by other members.
You are correct. Since the magazine is outside of the pistol grip then you have to jump through all the hoops just like you would building an AR rifle.
The upside of this is that once you put the BB in, you also don't have to worry about all the other CA restrictions on what is 'legal' for a handgun, such as a threaded barrel.
The BB rule also applies to rimfire in the case of pistols (where they are exempt from all the BS on a rifle). This is do to the slightly different wording in the laws. With regard to rifles, the law makes a clear difference between a center-fire and a rim-fire, but when it comes to pistols, that important differentiation is missing, hence I have a BB on my .22 AR pistol.