It looks like 1 bullet to me. It looks like it was a squib. Shooter recognized the failure. Probably pushed the bullet in and inch or so to the rifling. They tried to tap it out from the muzzle, got nowhere (and from the looks of the indent, may have hut the rifling) so they disassembled and tapped from the rear (indicated by more marks on the rear if the bullet). All that aside I don't see why anyone would take a 9mm HP, hollow out the lead, drop in another bullet (.32?), then crimp the jacket around it again. Its pretty involved.
The o.p mentioned it was found under the shooting bench and squib seems to be what consensus is as well... Now if claymore would just give us the picture!!! ;-) I don't have any HP bullets or I'd go drive one through a barrel myself.
But, GarySTL, the theory still remains provable by comparing the bullet to a cleaning rod.... Maybe snap a pic with a cleaning rod in one of the circles to see how it lines up?