The U.S. Attorney’s Office in Sioux City has announced a man from the South Dakota side of the Sioux City metro has been sentenced to four years in prison for trading guns for drugs.

Forty-year-old Brandon Christiansen is from McCook, Lake, South Dakota. He claimed to be a gun collector when authorities searched his home last year, but there were no guns in the house. Federal prosecutors say Christiansen illegally acquired as many as 56 guns over a seven and a half year period and traded the guns for drugs. According to a news release for the U.S. Attorney’s Office, some of the guns were semiautomatic and capable of firing off large-capacity magazines.

Purchase records presented in court showed Christiansen bought at least 23 guns from five different gun stores in Sioux City and Sioux Falls. Authorities say five of those guns were found during drug investigations that did not involve Christiansen.