update
On 07-08-2012, SB249 was amended and is currently in the Assembly's appropriations committee.
SB249 no longer deals with "assault weapon conversion kits" and now redefines what a "detachable magazine" is.
SB249 will redefine a "detachable magazine" to be any magazine that can be removed from a firearm without disassembling the firearm, this includes being able to remove a magazine with the use of a tool or tip of a bullet.
In essence, it bans "bullet button" style maglocks.
Therefore...
Semi-auto centerfire rifles, semi-auto pistols and semi-auto shotguns that currently use a "bullet button" style maglock to render it a fixed magazine firearm, would no longer be considered fixed magazine firearms and banned under CA's assault weapons laws.
If SB249 becomes law, prior to 07-01-2013, affected firearms will need to be modified to comply (made "featureless") or taken out-of-state or surrendered to law enforcement.