Other Definitions
obturate (dict)
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ObturateObturate means to block or obstruct. Obturation in firearms ammunition With reference to firearms and air guns, obturation refers to the process of a bullet or pellet, made of soft material and often with a concave base, flaring under the pressure of firing to seal the bore and engage the barrel's rifling. To ensure a proper seal, the pressure generated by firing the cartridge must be sufficient to obturate the bullet material. The formula used to calculate this for solid base bullets is: - Bullet's BHN x 1422 = Pounds per square inch
The constant 1422 is an empirically determined factor used throughout the ammunition and reloading industry; it is specifically tailored for calculating the pressure required for the obturations that occur in internal ballistics and should not be used for other purposes. Below is a chart containing various bullet alloys, the BHN, and the PSI required to obturate a bullet to the bore: | Material | | BHN | | PSI | | Pure lead | | 5 | | 7110 | | 1:20 Tin/Lead | | 10 | | 14220 | | 1:10 Tin/Lead | | 11.5 | | 16353 | | Pure copper | | 40 | | 56880 | Pure lead is very soft, and can be obturated by any firearm cartridge, but the pressures required are higher than those encountered in most airguns. To allow obturation in airguns, pellets use soft alloys in conjunction with a thin, concave base designed to obturate more easily. Some firearms ammunition, such as Foster slugs and hollow base wadcutter bullets, also use a hollow base to allow the bullet to obturate and conform to a barrel's irregularities (see internal ballistics). To prevent excessive deformation in high pressure rifle and magnum pistol cartridges, lead bullets are often covered in copper or another harder alloy. These bullets are generally designed to swage to fit upon firing.
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