Failure Analysis of Firing Pins in Small-caliber Automatic Rifles Under Low-temperature Conditions

LI Junan; QIAO Ziping; LEI Qinghua; XU Lining; ZHANG He

doi:10.7643/issn.1672-9242.2025.07.008

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Equipment Environmental Engineering ›› 2025, Vol. 22 ›› Issue (7) : 59-66. DOI: 10.7643/issn.1672-9242.2025.07.008

Special Topic—Application and Collaborative Evaluation Technology of Light Weapons in Complex Environments

Failure Analysis of Firing Pins in Small-caliber Automatic Rifles Under Low-temperature Conditions

LI Junan¹, QIAO Ziping¹, LEI Qinghua², XU Lining³, ZHANG He^1,*

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Abstract

The work aims to investigate the fracture failure of firing pins observed during low-temperature endurance testing of small-caliber automatic rifles, conduct impact fatigue failure analysis, and propose design improvements for firing pins. Macroscopic and microscopic examinations were performed on fractured firing pins from low-temperature testing. Additionally, mechanical property tests were conducted on the firing pin material under both ambient and low-temperature conditions to determine the failure mechanisms and performance characteristics in low-temperature environments. Material testing revealed that the firing pins exhibited higher tensile strength and improved low-cycle fatigue life at low temperature, while its impact toughness decreased significantly. Surface and fracture analysis showed that the firing pin tip had a rough surface with distinct parallel circumferential grooves. The study demonstrated a positive correlation between the firing pin material's tensile strength and low-cycle fatigue life under low-temperature conditions. However, impact toughness decreased by 29.3 % compared with that under ambient temperature, while maintaining a positive correlation with impact fatigue life. The observed surface roughness and machining imperfections created stress concentrations that accelerated crack propagation, reducing service life. In conclusion, for firearms operating in sustained low-temperature environments, it is recommended to select firing pin materials that maintain adequate ambient-temperature strength while exhibiting superior low-temperature impact toughness to ensure reliable ignition performance.

Key words

low temperature environment / firearm parts / fractured firing pin / impact fatigue / material properties / failure analysis

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LI Junan, QIAO Ziping, LEI Qinghua, XU Lining, ZHANG He. Failure Analysis of Firing Pins in Small-caliber Automatic Rifles Under Low-temperature Conditions[J]. Equipment Environmental Engineering. 2025, 22(7): 59-66 https://doi.org/10.7643/issn.1672-9242.2025.07.008

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