1.2g glass-filled nylon (hard plastic) ball round w/ seamline - mould cast. The manufacturing consistency is good, allows one to put rounds into a coffee tin sized target at 20 meters away with an HDR50, provided one's aim is not off.
1/2" calibre, 12.70mm, slight variance in manufacturing.
70% solid w/ hollow core. Will fragmentate into pieces and a few shards if struck at a suitable velocity against a hard surface.