By Steve Holland and Nandita Bose WASHINGTON (Reuters) -President Joe Biden unveiled a new rule to rein in so-called ghost guns and ban the manufacturing of the untraceable firearms on Monday as the administration faces growing pressure to crack down on gun deaths and violent crime in the United States. Ghost guns are privately made firearms that are not marked with a serial number and are difficult for law enforcement to trace when used to commit a crime. The Department of Justice’s final rule has been making its way through the federal regulation process for nearly a year and is likely to dr…