The 3Kg had a weight in the nose behind a drawn frangible cap. On the back of the weight was a striker pin and a 3-legged spider like spring.
The 'explosive' like a shot gun cartridge was in a large bobbin like aluminum slug. This is held off the striker by the spider's legs. The safety pin was an additional ground safety device.
When dropped on a target the nose, weight, and striker would stop and the slug would continue, squash the spider and bang. It was cheap and reliable. I was told the plastic body was biodegradable and the whole cist about £18.50.
Many components were undamaged after use but there was no interest in recovery and reuse.