I had a couple of the LEM Spitzer pellet/bullet moulds in the early 80s. The pellet/bullets were very heavy - the .22 is about 21 grains - and so the trajectory is very loopy. They seat on a driving band so aren't particularly accurate. A fellow at my club used to load them into .22 Hornet centrefire cases and liked them as a soft load. LEM also made a ball round as well. The .177 pellet/bullet was about 14 grains, about the same as a normal .22.
I think they might work OK in FAC PCP rifles over 25 foot-pounds but for 12 ft/lbs they are pretty much useless. Airgun pellets are best designed as the waisted cotton-reel model, with a long distance between the head band and the skirt. Bullet shapes are for firearms really.
They ARE great fun to make though. Apart from the risk of lead poisoning.
They come up on £Bay from time to time.