Seen in the June, 2018 issue of Guns & Ammo magazine, pages 40-53.
True Velocity is making ammunition, in a variety of calibers, with plastic casings. They offer a 40% weight reduction, and improved heat characteristics. Well, at least the chamber stays cooler. The heat has to go somewhere, so it goes down the barrel. The rounds also don't cook off. At all. Not even when they tried their best to make them do so. The casing eventually deformed and started to melt, but the powder never lit. Plastic's a pretty good insulator.
They also claim a dramatic improvement in case dimension consistency. One lot measured an SD of 3 fps, with a max deviation of 8 fps. That's unheard of in large production runs.
The casings, and thus the ammunition, are also cheaper than traditional brass. The company is currently focused on serving the military and law enforcement agencies. I'm sure the troops wouldn't mind shaving a few pounds off every case of ammunition.
What's the downside? They're probably a lot harder to reload.
Available in .223, .308, .338 Norma, .50 BMG, and 12.7 Soviet.