Odd (to me) 76mm round
 

A few of these showed up during a recent range sweep at the local base. The round seems like it is solid lead, and has a brass driving band bolted onto it. The driving band is just brass sheet shaped like a cup, and is held onto the lead bullet with three 5/16 NC nuts. The overall diameter of the round is approx 76mm, and the driving cup appears as if it was fired through a barrel that had just three equally sized lands and grooves.

Any ideas as to what this round is from?