Dynamic qualitative bolt force measurements for investigating influence factors on the pushout effect of small calibre ammunition

A small calibre weapon system consists of the weapon and the ammunition. In the case of bolt action rifles during the process of firing, the breech is a rigid bearing which prevents the casing from being pushed out. However, not the whole pushout force is taken by the bolt. Due to friction forces at the casing boundary, the chamber of the weapon can absorb a significant part of the pushout force. The duration of the pushout force is in the order of milliseconds. Piezoelectric strain gauges are capable of recording such short time events qualitatively. To increase the measurability of force obtained from raw signal, is filtered using a bandpass filter and applying a signal envelope. The results from the strain gauges are verified by a piezoelectric force washer. In this paper, two different lubrication states and two different casing materials are analysed to evaluate their influences on the force absorbed by the bolt. The analysis indicated that lubricated casings lead to bolt forces which are more than three times higher when compared unlubricated casings. The unlubricated steel casing also showed a significant lower bolt force when compared with the regular brass casing. However, this effect is reversed, if the casing is lubricated. This work demonstrates how to measure highly dynamic events. The acquired results can be directly applied to 5.56x45 bolt action rifles. These measurements may also have a significant influence on self-loading rifles, since the process of reloading is also dependent on the pushout force. The general application area is target competitive shooting and military purposes.