Pennsylvania Game News - May 2010 - 62

liseconds of time, creating tremendous gas pressure to where it sounds to us like an explosion as the bullet leaves the barrel. Just to show how much influence the primer has in powder ignition, its actual flame is in excess of 600 degrees, and the force of just a primer flame alone — no powder charge or bullet — actually exits the barrel and can severely burn or puncture whatever is within a foot of the muzzle. (Don’t try this.) With that said, there are significant differences in the power of pistol and rifle primers, as well as standard and magnum primers, although some manufacturers do make a primer that can be used for both standard and magnum cartridges. Cartridge cases have a certain amount of elasticity, but can take just so much pressure before they burst or crack. Typical revolver cartridges will range from 12,000 CUP (copper units of pressure) for the .32 S&W Long to the .44 Mag. with 40,000 CUP. Pressure limit differences are also inherent among various firearm designs. Lever actions that handle cartridges such as the .30-30 and .35 Remington can handle up to 42,000 PSI (pounds per square inch), while bolt actions can handle more than 60,000 PSI, for cartridges such as the .300 Remington Ultra Mag. So, it is the selection of the powder that allows us to remain within safe pressure limits within the confines of the case, caliber and firearm. In general, to reach optimum bullet performance (speed and accuracy) the ideal situation is to have the powder fill the case to where there is little or no air space between the powder and seated bullet. Having a full case allows the powder to burn in a steady, timely and predictable manner. Too much empty space in a cartridge can result in too much powder being exposed to the open primer flame too soon, causing dangerous peak pressures too early, before the bullet has a chance to move down the barrel, and in effect, lessen the pressure. Typically, small volume cartridge cases
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use fast burning powders that generate short, quick pressure curves. Powders designed to burn in larger volume cases, and pistol-length barrels, generate longer, slower pressure curves. With the tremendous variety of cartridge cases and powders, the preceding can be construed as an oversimplified statement, but it’s basically true. Exceptions are, for example, when shooting cast bullets in some large volume cartridges cases. Extreme examples of powder burning rates would be to compare a .25 ACP pistol cartridge using 1.5 grains of Winchester 231 fast burning powder to push a 50grain round nose bullet at 800 fps to a .300 Remington Ultra Magnum rifle cartridge using 85 grains of IMR 7828 slow burning powder to push a 190-grain bullet at 3,100 fps. If you were to reverse the powders, I’m not sure you could get enough 7828 in a .25 ACP case to push the bullet out of the barrel. On the other hand, far less than 85 grains of 231 could do some real damage to the rifle and the shooter. As you progress in your reloading, you will find there are certain patterns that factor into choosing powders. One such pattern that could dictate a powder change is using cases that are close to the same volume but necked to a different caliber. A perfect example of this is the .300 Savage cartridge compared to the .22-250 Remington cartridge. Both are from the same parent case and shoot many of the same powders well, but the .300 Savage works best with medium burning powders (IMR 3031 or 4064) and the .22-250 seems to be at its optimum with slightly slower burning powders (H380 or AA2230). Another factor that could determine powder selection is bullet weight/length. If we take a cartridge case and use bullets of different weight and lengths (same caliber, of course), the lighter/shorter bullets take less time to reach their optimum speeds than do their heavier/longer counterparts. Therefore, the heavier bullets may require a slower burning powder. A perfect
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Pennsylvania Game News - May 2010

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