SANTA CLARA, Calif. - The 49ers have added two inside linebacker to the 53-man roster since the start of the regular season in addition to NaVorro Bowman, Michael Wilhoite, Shayne Skov and Nick Bellore.
The Raiders released Armstrong Tuesday. He became subject of an investigation for taunting a police dog in Pittsburgh on the team's trip to play the Steelers earlier this month, which he was not charged.
Armstrong (6-3, 220) is reunited with former Raiders defensive coordinator Jason Tarver, who serves as a the 49ers' linebackers coaching and senior defensive assistant. Tarver was Oakland's defensive coordinator from 2012 to 2014.
The Raiders added Armstrong after he was released by the Rams in Oct. 2014. He played in 21 games for the Raiders over the last two seasons.