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This graph shows different pressure curves for powders with different burn rates. The leftmost graph is the same as the large graph above. The middle graph shows a powder with a 25% faster burn rate, and the rightmost graph shows a powder with a 20% slower burn rate. Energy is the ability to do work on an object. Work is force applied over a ...
The first powders were called "MR" for military rifle powder. In the 1920s these powders were improved and the name was changed to IMR. Various different powder are produced and are given numbers to distinguish them. The different types of powder typically have different burning rates.
To obtain maximum accuracy, bullet weight and form are matched to the rifling twist rate of the barrel. Typically, 68 gr (4.41 g) bullets are used in barrels with twist rates of 1 in 13 inch (1 in 330 mm), while 1 in 15 inch (1 in 380 mm) barrel twists can accommodate lighter 58 or 60 gr (3.76 or 3.89 g) accurately.
For pure explosive damage, high burn rates or detonation speeds (and accompanying brisance) are generally preferable, but in guns and especially cannons, slower-burning powder decreases firing stresses. This allows for lighter, longer (and more accurate) barrels with associated decreases in production and maintenance costs.
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 that retard burning slightly.
Black powder produces gas at a predictable rate unaffected by pressure, while the gas production rate of smokeless powder increases with increasing pressure. [6] The possibility of runaway pressures caused smokeless powder to destroy many firearms designed for black powder and required much more precise measurement of propellant charges.
There are basic advantages inherent to the Short Magnum concept. The idea is that the short, fat powder column gives a more uniform load density and ignition rate and therefore a more consistent burn. This in turn should translate into improved accuracy and potentially moderate recoil due to more efficient use of propellants. [citation needed]
These loads were eventually dropped due to a combination of safety concerns, and newer smokeless powder rifle cartridges that offered even higher velocities, such as the .30-30 Winchester. [ 2 ] The first modern smokeless powder cartridge deliberately loaded by a major manufacturer to higher than standard pressure was the .38 ACP , originally ...