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Barrel link-up or link-up/cam-up in pistols without custom fit bottom lugs, occurs as the slide assemble continues to move forward and the barrel extension contacts the breechface causing the barrel to pivot upward on the barrel link (arrow). This causes the locking lugs on the top of the barrel to index with the corresponding locking recesses in the slide. Barrel link-up/cam-up in M-1911 pistols with custom-fit bottom barrel lugs is assisted by the camming action of the radiused, bottom front barrel lug surfaces as they bear on and cam upward on the slide lock crosspin.
Vertical barrel and slide locking occurs as the slide causes the barrel to swing upward on the barrel link as in figure 3A. Aggregate barrel, slide, frame, slidestop and barrel link dimensional tolerances determine the extend to which a given barrel will link upward and locking lugs will vertically engage in any given M-1911 pistol. Locked slide position (arrow, fig 3B) permits the disconnector to move upward. This action -see disconnector function below- connects the trigger and sear and prepares the pistol for firing.