Officers also confiscated high-capacity magazines, ammunition, several pounds of methamphetamine and cocaine, and about $600,000 in cash, according to a news release.
The eight search warrants were executed in connection with several investigations, according to the San Bernardino Police Department.
Most of the weapons were so-called "ghost guns" and modified automatic rifles.
Underground businesses were peddling the guns behind the facades of illegal storefronts, including an auto repair shop and a gun parts store, the Police Department said.
Correction: An earlier version of this story stated that $600 in cash was found. The article has since been updated to reflect the correct amount, which was $600,000.