Jon Hammar (shown here) and his friend were on their way to Costa Rica in August and planned to drive across the border near Matamoros in a Winnebago filled with surfboards and camping gear.
But Hammar's gear also included an antique shotgun with a barrel that's an inch too short to comply with Mexican law.
When the pair crossed the border and handed the paperwork to Mexican officials, they impounded the RV and jailed Hammar, saying it was illegal to carry that type of gun.
Family attorney Eddie Varon-Levy questioned the way Mexican officials measured the gun, because the measurements can differ depending on where they are taken on the barrel.
He said dealing with Mexican authorities has also been difficult. He said Hammar was brought to court a few weeks ago, where officials tried to convince him to plead guilty without a lawyer present.
"I am fuming," he said.