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Opponents of SB 249, authored by state Sen. Leland Yee (D-San Francisco), said the bill is a violation of their 2nd Amendment rights and will only make some rifles more dangerous.

If approved, it stands to ban hundreds of thousands of rifles commonly labeled assault rifles.

Right now, AR-15s and M-15s are legal because of what is known as a "bullet button" -- a safety device designed to slow down how quickly the user can replace a magazine. Without the button, the rifle with all of its upgrades is considered an assault weapon.

Authorities said a similar rifle was used in the movie theater massacre in Colorado last month.

Yee's bill intends to make the bullet button illegal, therefore outlawing the rifles all together.

"A gun manufacturer found a way to skirt the law and all I'm doing is just plugging that loophole," Yee told 10News in a phone interview.

"It would make me a criminal because my rifle would become illegal," said gun supporter and AR-15 owner Dr. Hans Wiederrich.

Wiederrich said hundreds of thousands of these rifles have been sold in California. He warned that making them comply with a new California law would actually make them more dangerous.

"More dangerous because now the magazines can be detached by just using your thumb and pulling the magazine out," he said.

Those magazines could also hold more than 10 bullets.

If SB 249 passes, it could go into effect January 1, 2013.