The Transportation Security Administration says the bags belonged to a 16-year-old and a 17-year-old who were returning from a school field trip to Europe.
TSA spokesman Jim McKinney says a bomb disposal crew determined the shells were inert and no one was ever in danger.
The teens told law enforcement they obtained the shells at a French World War I artillery range. It was not clear how.
TSA explosives experts believe they are French 75 mm shells.
They were seized Monday evening while the teens were transferring to a flight to Seattle.
The teens were questioned then allowed to travel onward. They weren't charged.
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