Those are rifle flechettes (and therefore not covered by the prohibition on SHOTGUN flechettes); the left round is a 5.6x57mm XM645 SPIW cartridge, for the US Army's Korean War-era "SPIW" (Special Purpose Individual Weapon) program; these were hand-loaded by IVI in Quebec at a cost of $3.50 PER ROUND , and fired off at a rate of 2,000 rpm. The right round is a .223 round made for the US Army's ACR (Advanced Combat Rifle) program. Both of these used angled tail fins to spin the dart (and hopefully, give it more accuracy), but they still weren't accurate enough to meet projections, so the idea was dropped. In terms of target effect, though, they produced a surprising amount of damage; because of their velocity (a lot higher than the "beehive"-style artillery flechettes) they could pierce a surprising amount of material, and if they hit flesh, they would "fishhook", causing real problems.