Semi-automatic pistols can be divided into a number of different types. These include pistols that use a blowback mechanism and those that utilize a short-recoil Browning-type mechanism.
With blowback pistols, only the slide moves relative to the frame of the gun upon discharge. The barrel of a blowback pistol is fixed to the frame but the slide is not secured to the barrel. Immediately after firing the pistol, the recoil force starts to drive the slide rearward commencing the extraction of the spent cartridge case. Accordingly, part of the extraction of the case occurs during the high-pressure period of the firing cycle. If the slide is too light the case is extracted too soon affecting the loading cycle. The blowback mechanism is typically used with low-powered cartridges. Semi-automatic pistols for higher-powered cartridges generally utilize a short-recoil mechanism.
With short-recoil operated pistols, both the barrel and slide move together rearward upon discharge of the gun. Prior to the firing of the cartridge, the barrel is engaged to the slide by a locking mechanism. After firing, the recoil force drives both the slide and barrel rearward, but since they are in engagement, the extraction of the case has not started. After the high-pressure period has passed, an actuator begins to disengage the barrel from the slide. The barrel travels a short distance before coming to rest forward of the magazine, hence short-recoil, and is completely disengaged from the slide. The slide continues and begins extraction of the spent cartridge case using its kinetic energy and the residual gas pressure in the barrel. After extraction, the spent case is ejected. The slide continues until full travel is reached.
In short-recoil operated pistols, the barrel may be locked to the slide by a number of locking mechanisms. The barrel may be provided with peripheral ribs, studs, lugs or other mechanism and may be rotated, cammed or otherwise engaged and disengaged from the slide. Alternatively, a separate locking block may be used to lock the barrel to the slide. A common method utilizing a locking block is the dropping barrel method as depicted in U.S. Pat. No. 4,915,011 hereby incorporated by reference in its entirety.
In the dropping barrel method of locking, the barrel is slidably mounted for straight line longitudinal motion, and the locking mechanism comprises a separate locking block provided with an actuation mechanism for engaging the barrel to the slide. The actuation mechanism comprises a cam in the frame to drive the barrel downwardly from engagement with the slide during initial rearward movement of the slide from the battery position and upwardly to engage the barrel to the slide during final movement of the slide to the forward battery position.
In metal frame pistols, the slide is usually secured for such movement by longitudinally spaced pairs of metal guide rails. The guide rails generally include four rails, one forward and one rearward pair.
In recent years there has been a trend in the firearm industry to utilize polymers in the manufacture of semi-automatic pistols, particularly in fabricating unitary frames therefor by injection molding techniques. Generally, in such frames, the front pair and rear pair or spaced guide rails are partially embedded in the polymer of the frame. The cam, which is part of the locking block, is assembled into the frame and held by cross pins. The locking block is located between the two sets of rails. Polymer frame pistols are desirable in that they are lighter than pistols with metal frames.
Currently, firearm manufacturers are making compact polymer frame pistols which feature a reduced length frame, slide and barrel as disclosed in U.S. Pat. No. 5,717,156, which is hereby incorporated by reference in its entirety. Compact pistols are smaller and lighter than standard size semi-automatic pistols. Additionally, the reduction in trigger reach and grip circumference of compact designs increases concealability and is thought to enhance shooting ergonomics. Compact designs are available for both low-powered and high-powered cartridges.
In some prior art compact pistols, there is a limit on the reduction in size of the pistols. The size limit is due to the fact that the guide rails and locking block are separate components. Given the separation of guide rails and locking block, and the configuration of prior art frames, a minimum distance between the guide rails and locking block is necessary.