Which step in the cycle of operation involves throwing the casing?

The step in the cycle of operation that involves throwing the casing is ejection. During the firing process of a semi-automatic pistol like the M9, once a round is discharged, the spent casing needs to be removed from the chamber to make space for the next round. This is accomplished in the ejection phase of the cycle.

The ejection is facilitated by the action of the slide moving rearward, which engages the extractor that grips the rim of the casing. As the slide continues to move back, it ejects the casing out of the ejection port, allowing a fresh cartridge to be fed into the chamber during the next phase. This crucial step ensures that the firearm can continue to operate effectively without mechanical failures that could arise from a spent casing being left in the chamber.

Understanding the ejection phase is important for the proper functioning of the M9, as it highlights the importance of the rapid cycling of rounds in semi-automatic operations.