A 21-year-old man prosecutor Chris Poole described as "a particularly dangerous street gang member" was given a maximum 21-month sentence in Federal Court.
Authorities said Leonta Demon Epps earlier pleaded guilty to being a drug user in possession of a firearm.
Judge Collier said Epps at one time was being considered for release "on time served." But he said Epps would not cooperate with probation officials and would not address the court at the sentencing.
Prosecutor Poole said he was advised that Epps had made threats against a cooperating witness, including by Facebook messages.
Epps was allowed to self-report to prison in a month.