Seth Horvitz, 38, was surprised when he got the military-grade rifle that sells for $2,000. The UPS label had Horvitz's name and address on it, but the invoice inside the box was made out to a gun store in Pennsylvania.
He says he had never held a gun before he felt the trigger of the rifle.
Horvitz knew it was illegal to have the gun and also illegal to drive with it in his car, so he called police to come his apartment.
"I would like to know how this type of mix-up could take place, especially with what's going recently, these mass shootings. I don't want to be in a situation where this type of weapon can just show up on someone's doorstep accidentally," he said.
Police confiscated the weapon and are still investigating how it ended up at Horvitz's apartment.
The Associated Press contributed to this report.