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xplore the definition and principles of bolt thrust and why this force is critical to firearm design
In firearms engineering, "bolt thrust" or "closing pressure" is a crucial concept, especially in the field of internal ballistics. When a firearm is fired, the backward force exerted by the propellant gas on the bolt or closing part of the firearm is called bolt thrust. This force not only has magnitude but also direction, so it is a vector quantity.
Bolt thrust is an important factor that cannot be ignored when designing weapons; the greater the thrust, the greater the pressure on the locking mechanism.
In the design of firearms, the size of the bolt thrust directly affects the strength of the locking mechanism. In order to resist the action of thrust forces, the design of the locking mechanism must be sufficiently strong, which often results in increased weight and volume of the component. Therefore, engineers must strike a good balance between performance, safety, and volume and weight when designing firearms.
Relative to the recoil of a firearm, bolt thrust is not a measure of recoil or free recoil. This allows it to more accurately consider the impact of the pressure generated by propellant combustion on the closing mechanism when designing firearms.
Calculation of bolt thrust
For a specific ammunition, the calculation of bolt thrust is relatively simple. The basic calculation formula is as follows:
Fbolt = Pmax * Ainternal
Among them, Fbolt is the size of the bolt thrust; Pmax is the maximum chamber pressure of the ammunition; Ainternal is the internal area of the propellant gas pressure acting on the bottom of the ammunition.
In order to simplify the calculation, the bottom area of the circular cartridge case is usually used for calculation. By calculating the area of a circle, you can get an approximation of the interior area:
Area = π * r^2
Pi here is approximately equal to 3.1416, and r is the radius of the circle. Of course, in actual situations, due to different production batches, it is not easy to measure the diameter of the bottom of the ammunition, and it may affect the accuracy of the calculation.
Friction effect
One complexity of bolt thrust is that the cartridge case expands and deforms under high pressure, potentially causing "sticking" to the chamber. This "friction effect" may affect the effective transmission of thrust, which must be specially considered in engineering calculations. During some tests, such as the NATO EPVAT test, technicians will lubricate the ammunition to reduce friction to promote high thrust levels.
How to actually estimate bolt thrust
In addition to using the inner case base diameter, the outer base diameter can also be used to estimate this diameter by simply measuring it. This method, while effective for estimating, also assumes an overly generous area and the resulting calculation is usually slightly conservative, thus providing a sufficient margin of safety.
The formula for calculation using the outer bottom area is as follows:
Fbolt = Pmax * AexternalWhere Aexternal is the external area of the bottom of the cartridge case.
This method is suitable for obtaining a good bolt thrust estimate, and engineers can make design adjustments for different situations. If the ammunition is placed in an overheated chamber, it may cause accidental discharge due to excessive temperatures, which requires special attention during the design process.
Estimation of bolt thrust for boxing and rifle ammunition
For example, based on different boxing bullets and rifle bullets, designers can use C.I.P. data tables to obtain standardized data. These data are of great significance for estimating the bolt thrust of various ammunition.
When designing a new weapon, engineers need to conduct in-depth analysis of this data to ensure that the selected materials and structural design can meet performance requirements and safety standards. However, the balance between strength and weight is often a difficult problem. Is there a better solution that can balance performance and safety?
