What is a “bullet button?”
The mag release on Ca legal Hi caps has been removed so that you cant just drop a mag out with your finger and slap on another mag.
Smart manufacturers replaced it with a recessed release that could be actuated with the tip of a bullet so that you could still remove the mag for cleaning and be within the letter of the law.
http://www.riflegear.com/p-58-ar15-bullet-button.aspx
When they outlawed “assault” (cf their definition) rifles, one of the criteria happened to be an external/quick mag release. So, californians devised a “button” that requires using something with a sharp tip to release the mag. Something like a pointed bullet. Hence, the “bullet” button.
Your magazine release button.
See that funny looking piece of metal at the front of the trigger guard that covers the magazine release? That's a "bullet button." In essence it "permanently" attaches the magazine. It's is not a loophole or workaround, rather it is "verbatim compliance" with the law as written. There was a court ruling subsequent to the ban that defined "permanent" as "requiring a tool to remove" and stated that a bullet, in that circumstance, was a tool.
What's up with Yee is that he watched a show on KCBS in SF where they took an AR and attached a "Mag Magnet," which holds itself to the bullet button by magnetism. Having a Mag Magnet attached to bullet button is already illegal in CA. Was KCBS charged with felony manufacturing of an assault weapon? I think not. But Yee saw the show, probably when he wasn't cruising for hookers in Tenderloin (has cautioned by the SFPD 2x for doing so). and decided to get some newstime, which KCBS promptly provided. Yee says he is only going after the Mag Magnet but legal analysis of his poorly written bill indicates it could affect bullet buttons as well.
I wonder if I could get Yee to follow me to the range and release my magazines for me. I am certain it would be 100% legal under CA law since he is a tool.