Which commercial gunpowders are progressive powders and why?

Answer 1

"Regressive", "Neutral", and "Progressive" describe the propellant grain geometry. Nearly all commercially available smokeless powders are regressive. The instances where a neutral or progressive propellant is needed is in artillery applications where the desired velocity is coupled with an extremily heavy projectile (compared to civilian ammo). The cost to create a progressive propellant is beyond the price a cilivian could afford and honestly involves more mathematics to safely hand-load. As a regressive propellant grain burns the surface area decreases (burns on the outside towards the center). As it is comsumed less material is being converted into gas, the force driving the projectile through the barrel. As the projectile passes through the barrel the space behind it increases. This increasing space needs to be filled with gas in order to increase the velocity of the projectile. A regressive propellant has a decreasing supply of gas to fill this increasing space. With a neutral propellant the surface area of the grain that is being comsumed is constant (the amount of gas generated remains constant over time). A neutral grain would have a hole in the center; as the center burns the hole gets bigger (more surface area is burning), and as the exterior surface burns the grain is consumed to a smaller size (exterior surface area decreases). With a progressive propellant the surface area increases as the grain burns (the amount of gas generated increases over time). This is accomplished by multiple holes in the grain. The best way to visualize this is to draw a large circle on paper. Draw four circles spaced evenly inside the circle. The surface area is the total circumference of each circle. This is the initial surface area of the grain. To simulate the surface area after burn is initiated for a time...draw a circle slightly inside the larger circle and draw slightly larger cirlces around the the inner circles. The total circumference of these new circles is the increased surface area. And like all good students...don't try this on anything except your paper!