A man arrested outside the Whitefish Police Department with a homemade firearm has been convicted of federal weapons charges.

During a hearing in U.S. District Court in Missoula, Andrew Scott Benningfield, 37, of Whitefish pleaded guilty Tuesday to possession of a firearm without a serial number.

His sentencing hearing is scheduled for March 27.

According to court documents, officers inside the Whitefish Police Department heard a loud banging noise from outside the back door in August 2007.

Upon exiting the building, they saw a trash can had been knocked over and a lone man walking away with something in his hand.

Officers arrested Benningfield for disorderly conduct and criminal mischief after he admitted to pushing the can aside, reportedly because it was in his way.

Benningfield then complained about getting harassed by law enforcement and said he was getting even, according to court documents.

Authorities confiscated the object Benningfield was carrying, a short length of metal pipe held by a vise grip with a cap and what appeared to be a firing pin on one end and a piece of cloth on the other.

When the device was disassembled, federal explosives experts identified it as a directional mine or a homemade gun.

Inside the pipe was a live .30-30-caliber round held by a piece of rubber hosing. A broken drill bit was positioned directly over the primer.

Upon searching Benningfield's truck, investigators found two more cartridges with the rubber hosing already in place. Also found were 96 other rounds of ammunition and tools that could have been used to manufacture the device.

In exchange for Benningfield's guilty plea Tuesday, prosecutors dropped possession of a destructive device and possession of ammunition charges.

Because he was committed to a mental institution in the past, it is illegal for Benningfield to possess a firearm or ammunition.

He faces a maximum penalty of 10 years in prison, three years of supervised release, and a $10,000 fine.

Reporter Nicholas Ledden can be reached at 758-4441 or by e-mail at nledden@dailyinterlake.com