The Glock 19 pistol magazine was discovered in a storage locker in Las Vegas on Monday, with the money inside.
The gun’s owner, John Mabry, told police that he had given it to a friend for protection, and when the gun was opened, the cash was gone.
The friend then discovered the gun in his backpack, which was loaded with ammunition.
He was arrested on suspicion of theft and carrying a concealed weapon.
Mabry told police he had received the gun from a friend, who said he wanted it for a hunting trip, according to the Las Vegas Review-Journal.
The Glock 19, a 9mm pistol, was sold by an unidentified buyer in 2014 for $5,000.
A total of $10.3 million worth of firearms were purchased between 2016 and 2019.