We somewhen discussed the “Alpha” projectiles here.
As the name is very common I will specify the ones I have in mind:
It is a saboted and cross shaped projectile (seen from the front) which is twisted in the average shape of a rifling.
I know these existed in 9x19, 12.7x99 and 12 GA.
Did other calibers exist?
Did this development lead to anything or were these projectiles ever manufactured in scale?
Who designed or patented these?
When did this happen?
Are images of all of the known calibers available?