How to use obturates in a sentence? Find typical usage patterns (collocations)/phrases/context for "obturates" and check conjugation/comparative form for "obturates". Mastering all the usages of "obturates" from sentence examples published by news publications.
Another important function provided by the cartridge is to seal the rear of the chamber. During firing of a cased cartridge, the pressure in the chamber expands the metallic case which obturates to the chamber. This prevents gas exiting from the rear of the chamber, and it has also been experimentally shown to provide a significant amount of support to the bolt. Without the case to provide this seal, the firearm design must account for this and provide a means of sealing the rear of the chamber.
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Upon firing, the projectile expands under the pressure from the chamber, and obturates to fit the throat. The bullet then travels down the throat and engages the rifling, where it is engraved, and begins to spin. Engraving the projectile requires a significant amount of force, and in some firearms there is a significant amount of freebore, which helps keep chamber pressures low by allowing the propellant gases to expand before being required to engrave the projectile. Minimizing freebore improves accuracy by decreasing the chance that a projectile will distort before entering the rifling.
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High pressures, such as those commonly encountered in maximum loadings of magnum revolver cartridges or rifle cartridges, often result in significant problems when coupled with cast or swaged lead bullets. It was long thought that the high temperatures melted the base of the bullet, but this is no longer thought to be the case. Instead, the high pressures allow propellant gas to escape past the bullet, causing gas cutting, which increases lead deposits in the barrel and unbalances the bullet. A gas check provides a thin layer of harder but still malleable metal on the base of the bullet that obturates to provide a seal and prevents the propellant gas leakage that causes gas cutting, and helps the bullet grip the rifling.
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To ease the force required to load the projectile, these early guns used an undersized ball, and a patch made of cloth, paper, or leather to fill the windage (the gap between the ball and the walls of the bore). The patch provided some degree of sealing, kept the ball seated on the charge of black powder, and kept the ball concentric to the bore. In rifled barrels, the patch also provided a means to transfer the spin from the rifling to the bullet, as the patch is engraved rather than the ball. Until the advent of the hollow-base Minié ball, which obturates upon firing to seal the bore and engage the rifling, the patch provided the best means of getting the projectile to engage the rifling.
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Before the projectile leaves the gun barrel, it obturates the bore and "plugs up" the expanding gas generated by the propellant combustion behind it. This means the gas is essentially contained within a closed system and acts as a neutral element in the overall momentum of the system's physics. However, when the projectile exits the barrel, this functional seal is removed and the highly energetic bore gas is suddenly free to exit the muzzle and expand in the form of a supersonic shockwave (which can be often fast enough to momentarily overtake the projectile and affect its flight dynamics), creating a phenomenon known as the muzzle blast. The forward vector of this blast creates a jet propulsion effect that exerts back upon the barrel, and creates an additional momentum on top of the backward momentum generated by the projectile before it exits the gun.
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