The 25mm shell was actually fired from a M2 M3 Bradley, LAV-25 Marine APC. This is a cool novelty item for a desk or gift.  It has a  25mm casing with a plastic projectile (bullet). They make great paper weights and fun to have. 

Features & Specs

• Measures approx. 8" tall.
• Inert with no powder or primer
• Can not be re-used
• Great as a desk novelty item
• Dummy ammo can not be shipped out of the U.S.