What is it that makes gunpowders burn at different rates? Is there more of a certain ingredient, is it "packed" or compressed tighter, or what? I don't know what all goes into a gunpowder, but was just wondering what makes the burn rates so different.

Thanks!!

And shape. The properties of the propellant are greatly influenced by the size and shape of its pieces. The specific surface area of the propellant influences the speed of burning, and the size and shape of the particles determine the specific surface area. By manipulation of the shape it is possible to influence the burning rate and hence the rate at which pressure builds during combustion. Smokeless powder burns only on the surfaces of the pieces. Larger pieces burn more slowly, and the burn rate is further controlled by flame-deterrent coatings which retard burning slightly. The intent is to regulate the burn rate so that a more or less constant pressure is exerted on the propelled projectile as long as it is in the barrel so as to obtain the highest velocity. The perforations stabilize the burn rate because as the outside burns inward (thus shrinking the burning surface area) the inside is burning outward (thus increasing the burning surface area, but faster, so as to fill up the increasing volume of barrel presented by the departing projectile).

I'm no ballistician but from what I've read, burn rate is determined by how the powder is made. Some powders have more nitroglycerine than others. Some powders have coatings that slow down the burn process. I would guess that even the shape of the granules contributes to their burn rate (flake,ball,extruded).
There's probably a lengthy discussion on gunpowder manufacturing on Wikipedia. Handloader magazine has articles about different powders in almost every issue.My 2 cents worth.....

Thanks guys! I wonder if a person could make powder themselves?? I think it would be a pretty heavy regulated thing, but I'm starting to wonder if it can be done. Perhaps black powder would be easier??

Very easy.

In our era of "homeland security", it might not be worth the trouble.

The coatings that are applied to powder by the manufacturer is what determines burn rate as does the chemical, and physical characteristics (ie stick vs ball vs spherical) make up of the powder as well.

Most powders have this coating applied to the surface of the powder after the powder is dry, and thus the coating is layed on the surface. Some such as RL17 have this "coating" applied while the powder is still wet and thus it penetrates thru the whole powder, thus controlling the burn speed "better" or "differently" than traditional methods. One reason the RL17 often generates more FPS than other similar powders, as this gives a longer pressure curve at similar pressure peak as other powders in the same burn rate class.

Regards,
Rog