Was originally developed under a US GOV R&D contract - polymer cased ammuntion to save brass and weight. In the end, the increased cost and marginal incremental improvement caused the military not to convert to it as expected, dooming the companies who tooled for its manufacture since they were stuck holding very expensive equipment with no market.
If I recall, it offered like a 10% reduction in ammunition weight, which would allow a soldier to carry 11% more ammunition for the same weight, but it cost like 2x to manufacture.