Hi Spotter, if only I did have the skill to make such things, there are/used to be some very very good metal turners out there.
To answer you question......hundreds of rounds over 20mm so there's plenty more to be photographed, its a good job you've got an experimental section.
I tend to buy/swap those wierd rounds that nobody bothers with, possibly because the're not quite sure what they are??
Regarding the projectiles in the photos they are all experimental Rheinmetall projectiles. From left to right:
Type 4 - sabot base weight 53 gram, Tungsten core weight 288 gram, plastic sabot weight 45 gram, rubber gas sealing section projectile weight 390 gram.
Type 3 - sabot base weight 59 gram, Tungsten core weight 289 gram, plastic sabot weight 47 gram, small copper driving band projectile weight 396 gram.
Type 5 - sabot base weight 23 gram, Tungsten core weight 303 gram, plastic sabot weight 53 gram, driving band is part of sabot projectile weight 380 gram.
Type 2 - sabot base weight 51 gram, Tungsten core weight 306 gram, plastic sabot weight 53 gram, white plastic driving band projectile weight 410 gram.
That's about all I know about them. These are only 4 of the series of 12 that I have listed. They were produced over the period 1980-1990.
Dave.