How many semi-automatic guns are in circulation the us?

According to the National Shooting Sports Foundation (NSSF), there are approximately 18.5 million privately-owned semi-automatic rifles in the United States as of 2021. However, this number only includes semi-automatic rifles that have been manufactured and imported legally. It does not include semi-automatic rifles that have been produced illegally or imported illegally. Therefore, the actual number of semi-automatic rifles in circulation in the US could be higher than 18.5 million.