Right, another unknown.
.38 Special brass, trimmed to about 21.5mm-22mm. Necked down to about 8mm with a 4mm neck. The rim diameter appears to have been turned down (No chamfer, sharp edge, evidence of tool marks) to 10-ish mm. OAL 32ish mm.
Photo to follow.
Sorry again about the “about” and “-ish” measurements.