This die was developed for the black powder shooter to achieve more efficient powder burn in large capacity cases. By compressing the powder and leaving a passage down the center of the powder charge, powder will ignite evenly through the case. Reports of lower velocity deviations and cleaner burning and improved accuracy using this system have been reported. This allows for maximum ignition within the case before the bullet engages the rifling. Properly done the powder will stay in place even during vehicle or airline flights, we know as we traveled thousands of mile with no problems. Comes with instructions and a 45-70 compression rod, other rods for other calibers available separately. For use with black powder only, leave no air space under your seated bullet.