Well, it hasn't kept metal out of the ocean either. It's all trash, and brass is considered a pollutant by most standards. Most brass cases are 30% zinc, which is bad. The difference is that with a highly biodegradable compound, missed rounds can be left. With brass, 99% must come home. Ever policed 99% of your brass after a 20k round day on a range with a firing line over a quarter of a mile long? But it doesn't stop there. Brass required its own recycling/salvage program. That alone is massive hours and even requires dedicated employees. Plastic cases can integrate into programs that already exist. They Army, for instance, actually sells its recyclables. However, brass was mostly sold for use in its existing form. Big difference in programs. Nevertheless, the big savings comes in weight and heat. True Velocity's 6.8 is a larger, more lethal round than 5.56, and it weighs less. So not only do we get a better round, we can carry more of it and still weigh less. Plus, the poly casing is a better insulator than brass, meaning weapons stay cooler. That is particularly important on the squad automatic weapon.