Abstract: Double action, hammer trigger mechanism for a semi-automatic firearm (10) with a spring loaded slide (12) having a cam surface (28), a pivoting sear (46) to hold the hammer (20) in a cocked position and a transfer bar (26) connected to a pivot pin (54) on the trigger (24). The transfer bar has a cam finger (30) to move the transfer bar down when the slide moves in a rearward direction during firing. When the sear is holding the hammer cocked, a second finger (62) on the transfer bar is arranged to engage a single action let-off pin (56) on the sear and pivot the sear when the trigger is pulled so as to release the hammer. The cam finger also moves the transfer bar down when the slide is stationary and the trigger is operated. The transfer bar has a notch (60) receiving a double action let-off pin (58) on the hammer to cause the transfer bar to pivot the hammer in a cocking direction as the trigger is pulled.

Abstract: A readily replaceable bolt face for a firearm (10) with a movable slide (12) that strips a round from a magazine, extracts the spent round from the firing chamber and then ejects the round from the firearm by means of an ejector. A bolt face insert (32) has an external configuration that is common to a range of calibers, but with a bolt face side (66) designed to fit the rim of a specific caliber or calibers having the same rim dimension. The insert may be replaced to fit a different caliber without replacing the slide. The bolt face insert is provided with a slot (62) for the ejector and a groove (60) to accept an extractor for the specified caliber.

Abstract: Frame construction for a firearm (10) with a frame (18) and a slide (12) constrained to move longitudinally between a forward and a rearward position but which is also removable from the frame. A recess (39) in the side of the frame contains the Kammer trigger mechanism (26, 38) that is accessible through a side opening (40) in the frame. A thin side plate (42) drops over the side opening and is held at its side edges and bottom edge by flanges (50) an the side plate overlapping congruent grooves in the frame and is held in place an top by the slide. After removing the slide in the conventional manner, the side plate can be slide upwardly and removed using a finger cutout (48) in the side plate.