Fluted chambers are longitudinal flutes which are deeper at the forward end of the chamber and taper off towards the rear. These allow the gases produced on firing to flow back over the outside of the cartridge case during firing. This counters the internal pressure and ' lubricates' the case, thus facilitating the extraction process. This is utilized in blowback and delayed blowback weapons where pressures are relatively high, thus making extraction difficult (Figure 4.18).
Figure 4.18 Longitudinal fluted chamber.
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