This is a fragmentation test cartridge. I have seen a wide variety of them over the years. Almost all air-to-air and ground-to-air warheads used on missiles are pre-fragmented (typically steel cubes packed/glued together into a warhead housing) so they throw a well defined pattern of fragments. Many have fragments of different weights/sizes to provide both high fragment density and higher penetration by the larger fragments to do major damage to the harder parts of the target aircraft like the engine. These cartridges are used to test aircraft and engine hardware to see how badly it is damaged by a missile. The velocity is adjusted to simulate different standoff ranges.
The first ones I have seen were designed to simulate SA-2 warheads. I have seen variations in 30-06/ 7.62 NATO /50 BMG, but these typically had a single steel “fragment”. Most were in 30mm and fired from a GAU-8 case and contained a cluster of steel squares. I have not seen this exact style before.
Note that the AIM-9 Sidewinder missile warhead was an exception. The warhead (or at least the earlier warheads) were a continious rod which expanded laterally out from the missile in a circle of increasing diameter and was designed to cut an aircraft in half. Very impressive in the slow motion test films I have seen, and the AIM-9 proved pretty effective in combat.