Board Members __

It has been my (perhaps erroneous) understanding that "Relative Quickness" represents a "burning" characteristic of gunpowders on a percentile basis compared to Bullseye being at 100%. My questions are: What are the mechanics (not the mathematics) of the procedures used to determine the value?. Is it merely another way of expressing our (misleading) concept of "burning rate"?

All donations are gratefully accepted.

Robert

FWIW, excerpts from the current draft of a Powley-Howell article that I haven't finished yet �

"The original technical meaning of the term ["burning rate"] refers to the linear burning rate of propellants � how rapidly the surface of the typical propellant granule shrinks inward from where it was when it started burning, toward the similarly retreating opposite surface of the granule. (See Figure 1.)

"The closest distance between any two surfaces of a propellant is known as the web. The powder is all burnt when the burning of these two surfaces meets each other midway between the original surfaces of the granule. By "burning" in relation to propellant powders, we mean the process that transforms the solid propellant into the gas that propels the bullet. This transformation occurs only at the surfaces of the propellant granule, as the process burns away the surface and opens a new surface to the process.

"Velocity depends on time and distance. One half the web is the distance, and if the time of burning is known, we have the average velocity of transformation, that is, the average linear burning rate. For a typical nitrocellulose propellant powder in an average rifle cartridge, this burning rate is up to about twenty inches per second (20 in./sec). In other words, as the surface burns, it retreats toward the opposite burning surface at about twenty inches per second.

"This is better stated as about 0.0004 inch per second (in./sec) for each pound per square inch (lb/sq in.) � (about 0.0004 in./sec per lb/sq in.).

"How fast is that? Notice that the rate as specified depends on the pressure. No matter in what kind of complete enclosure the powder burns, the pressure it produces is changing as a result of the evolving gas. As the evolving gas raises the pressure inside the enclosure, the linear burning rate of the powder granule increases � and it in turn raises the pressure, which in turn increases the burning rate, and so on, until the burning stops.

"In this example, you see, we simply can not tell what the burning rate is without stating the pressure. With the pressure changing, the average rate doesn't tell us anything at all useful, so a burning rate is not specified as a simple number. The burning rate is actually some kind of an algebraic equation containing one or more constants like the 0.0004 mentioned above as an example....

The latest and best way [to determine the burning rate of a powder] is to fire it in a gun equipped with a piezo-electric pressure gauge to obtain a pressure-time curve. This curve is differentiated by a calculus procedure to find the various slopes. This is compared with other complicated interior-ballistics equations that describe the observed behavior of the gun. By appropriate mathematical analysis, a burning-rate equation comes out that describes the observed facts. Depending on the particular equation thus developed, the constants may be used for the same powder in other guns.

"The older way is to fire a sample of the powder in a bomb equipped to give pressure-time curves. A bomb is a closed vessel in which an explosive, propellant, or other substance can be burned under tightly controlled conditions and the results observed and recorded. If a bomb is loaded to produce bursting pressures, it has destructive military use. If it's loaded in a laboratory so it doesn't burst, the propellant can be burned with the bomb placed inside a calorimeter to find the heat-energy content of the propellant. A straight pressure bomb used in the laboratory may give the required pressure-time curve. This is the most popular way to get burning rates from the curve slopes. Perhaps this is because the pressure-bomb measurements can be compared with those from the thermal bomb to find other characteristics of the propellant."

Good to see you back at the key board Ken- we have missed your wisdom. I hope this means that you are going to be in SD next summer.