Sam Jones was sentenced to spend 366 days in federal prison for his hand in a drug ring … even though the feds wanted him to serve 5 years.

Jones — who recently pled guilty to conspiracy to sell more than 10,000 pills of Oxycodone — was hit with the sentence Monday in federal court in Los Angeles.

Before sentencing, we’re told Jones begged the judge for mercy … explaining he’d lost everything — including his dog, his car, and his acting gig on “Blue Mountain State” — due to the drug charges.

The judge apparently bought it … and said he was cutting the actor a break due to his “minor” role in the drug deal.

Jones will have to surrender to authorities once it’s determined which prison he’ll call home for a year.