A police ballistics test has shown that a rifle carried by a St. John’s University student was loaded and ready to fire when he was arrested this week on the Queens campus. His lawyer said yesterday he meant no harm.

A fellow student and university security officers tackled the student, Omesh Hiraman, 22, Wednesday afternoon after he was noticed striding through campus wearing a Halloween mask and carrying a muzzle-loading rifle wrapped in a black bag.

Mr. Hiraman’s attorney, Anthony Colleluori, said a combination of physical pain from recent back surgery, depression, and a diagnosis of schizophrenia led to the incident.

“My client is suffering badly from health issues — both mental and physical,” Mr. Colleluori said.

“His big dream was to join the Navy and become an astronaut, and his dream was crushed,” he added.

Mr. Hiraman has suffered from scoliosis since childhood, the lawyer said, which forced him to drop his plan to enter the Navy. He then became depressed, left Cornell University, and was diagnosed with schizophrenia, Mr. Colleluori said. After a year off, Mr. Hiraman was trying to restart his academic career at St. John’s this fall.

“The pain, I don’t think he was up for it,” Mr. Colleluori said, adding about his purchase of a gun last week: “My thinking on that is it was a protective action, but I can’t rule out suicide.”

Mr. Hiraman was moved to a psychiatric ward at Bellevue Hospital yesterday as he awaits his arraignment today on charges of criminal possession of a weapon. It is illegal to have a gun, even of the old-fashioned black powder sort, in the city without a permit or NYPD registration.

Police fired his weapon yesterday afternoon in front of attorneys to determine whether it had been operable. They found that the gun, a Wolf rifle that breaks in the middle and is charged with black gunpowder, had been loaded with a powerful .50 caliber ball.

“It would have worked,” a police spokesman, Deputy Commissioner Paul Browne, said.

Police officials said Mr. Hiraman had bought the gun on September 21 at Dick’s Sporting Goods in Poughkeepsie at a pre-tax price of $179.99, along with some accessories. He paid cash and didn’t show identification, police said.

Police were seeking a warrant to search Mr. Hiraman’s computer yesterday afternoon after he reportedly sent an e-mail message to a local lawyer asking about which government agencies would be notified if he were to buy a gun, police officials said.

The police commissioner, Raymond Kelly, said he could not comment on Mr. Hiraman’s mental state, but said St. John’s had not been made aware of any “red flags” in Mr. Hiraman’s behavior before the incident.

Mr. Kelly praised the university’s new emergency text messaging system, which he said “worked like a charm.”

The commissioner also honored the student who helped security guards arrest Mr. Hiraman, Christopher Benson, 21, a police cadet. “At one point I was afraid he would turn into the crowd and start shooting,” Mr. Benson said at an afternoon news conference with Mr. Kelly. “I was pretty relieved that it didn’t go off.”