IMR 4955™ This new Enduron™ extruded powder is a top performer with such great cartridges as the 270 Winchester, 25-06 Remington, 280 Remington and 300 Winchester Magnum, and many, many more. It falls directly between IMR 4451 and IMR 7977 in burn speed, providing top performance for all such cartridges used for big game. As with all Enduron powders, it is temperature insensitive, clean burning, minimizes copper fouling and is totally safe for the environment. Adding this propellant to the Enduron line filled in an important place in the chart. IMR 4955, plus the original three, provides top loading for cartridges from 223 Remington to the massive 500 Nitro Express Magnum.