Pistol Phylogeny Part 4 – Locked
Locked breech systems add another wrinkle to the discussion, in that they include mechanically locking components. This means that these systems can be categorized both by the type of locking mechanism they employ, and by the manner in which they drive the system to unlock it. This can, and has, led to a wide variety in design combinations that can make categorization a bit difficult. The author has finally ordered his mind to first separate them by the overall operating philosophy (gas or recoil driven), secondly by the method in which the philosophy is employed, and thirdly by the mechanism used to lock and unlock the gun itself. For the sake of brevity, he has also limited both his collecting and writing to guns that were commercially available in numbers as to be “reasonably” available on the open market. He would certainly appreciate information on combinations appropriate to these criteria that he may have missed.
The advantage of locked breech systems comes from the strength inherent to the locking itself. Containing the gas pressure of a fired cartridge makes for a delicate balancing act in unlocked systems, and some rather clever physics equations in delayed systems. In locked systems, the pressure is inherently contained, and the engineering is left to focus on how and when and by what force the barrel and breechface are separated.
Gas operation is a set of systems far more common in the world of long arms, with relatively few examples of gas operated pistols; and of those, all but a few have remained in the mere prototype phase. In fact, the author is currently aware of only two “reasonably” available models in this category, and both are interestingly in “magnum” chamberings. Perhaps after tapping and siphoning the gas off the barrel, more traditional pistol rounds lack the needed “umph” to pneumatically drive the system? Or perhaps gas operation is just too dirty, hot, and complex for most handguns to bother with when the job can be done any number of other ways?
In either case, gas operation differs from gas delay pretty starkly. In gas delay systems, the gas is used to exert a force against the slide and counter/delay its rearward travel. In gas operated systems, gas pressure is employed in an opposite manner, to accelerate the slide/bolt into the rearward direction. In long arms this traditionally takes several forms – gas flappers, gas traps, short stroke pistons, long stroke pistons, direct impingement, the AR platform modified direct impingement, etc. However, in pistols, these traditional categories are a good deal muddier…
For reasons that will soon become apparent, we must briefly describe direct impingement. This is the most straight forward form of gas operation. In this setup, gas is tapped out of the barrel, down a tube, and directly onto/into the slide/bolt/bolt-carrier, which is then forced rearward until the gun unlocks and opens. Long stroke systems work similarly, except instead of venting the gas back into the slide/bolt-carrier itself, it is used to pressurize a gas chamber and drive a piston and operating rod backwards, which is in turn attached to the bolt-carrier, which moves and unlocks the action, etc.
There is only one gun that the author knows of that operates similar to these manners, and that is the meme-y-ist of pistols – the Desert Eagle. In this gun, the gas is actually siphoned off directly in front of the chamber, before running forward in a tube parallel under the barrel. At the front end of the barrel, the gas is vented downward into a chamber that is sealed on the rear end with a piston head attached directly to the slide. The gas pressure then forces the slide rearward against its hefty mass and spring pressure. As the slide begins to move backwards, the rotating bolt head (very similar to an AR) remains locked into the otherwise immobilized barrel trunnion. The slide (acting as the BCG would in an AR) rotates the bolt head in a camming action as the two are drawn apart, until finally the bolt turns enough to unlock and open. To ensure the bolt head remains aligned during the rest of the operation, a spring-loaded plunger (otherwise pressed back into the slide when in battery) temporarily rides forward and in between two of the locking lugs.
The consternation here is whether this design is more akin to a direct impingement or long stroke action. The piston head is a very short piece such that the slide touches the gas chamber, and since the slide is all one piece, it could be argued that the gas is directly impinging on the slide. That said, the piston head is actually a separate piece affixed to the slide, and the two forward extending slide arms can be seen to operate as an operating rod, thus providing a basis for a long stroke categorization. Perhaps this is splitting hairs, but the author has determined to call it a long stroke system, because it sounds more symmetric when paired with the short stroke gun that shall be addressed next.
(It should be noted that the author does not consider himself to be totally ridiculous, as he did limit himself to the far more practical and comfortable .357 magnum version of the gun.)
Much less questionable in the nomenclature of its design, is the Wildey Survivor. This similarly magnum hand cannon utilizes a short stroke system in which gas is vented from the barrel and used to accelerate a block that slides on a piston surface for a short distance. The block is then driven into the slide, and moves it for a short distance before reaching its rearward extent of travel. The slide absorbs enough momentum from the brief strike to carry through the rest of the stroke and cycle the next round. Locking is achieved in much the same way as the Desert Eagle, via a rotating bolt head in the rear barrel trunnion.
The difference between long and short stroke gas operation has to do with how far back the piston/operating rod travel. In a long stroke system, these are generally attached to the rest of the rearward cycling parts, and they move the full length of the action. In a short stroke system, the piston only travels a much shorter distance, essentially punching the cycling parts into motion, but not following through with them for the whole stroke.
While gas operation of locked breech, auto-loading systems are significantly more common in long arms than handguns, the opposite is true for locked recoil operated systems. There are certainly a healthy number of long arms that have used these systems, but as most of the designs to follow include the movement of the barrel as a critical component, making rifles and shotguns with so many moving parts fell mostly out of favor in the first half of the 20th century. These considerations are far less challenging to adapt to handguns, as their size, recoil energies, and acceptable accuracy are all typically smaller. While many larger machine guns, cannons, etc. utilize recoil systems, these are often more specialized and emplaced, and for the common collector, locked recoil guns most often take the form of pistols.
Recoil operation can be compared to direct blow back to understand the relatively simple concept – rearward directed recoil energy is used to open the breech. However, as already described, locked breech guns must additionally find a way to decouple the barrel and breechface safely. How this is done is the subject of a myriad of patents and designs, many of which are categorized as follows.
The journey through the actions of locked recoil driven pistols begins on the “is that really locked?” end of the spectrum, with the inertia locked system of the Benelli B76 and related models. In fact, these guns are most commonly identified as delayed systems, which does also hold some valid points. The author has actually owned one of these guns for a short time (before a defect in the frame sadly rendered it totaled), and would best compare it to a 1980s Italian sports car – a sleek, smooth, and stylish design covering a series of esoteric features that result in simultaneous genius and insanity (for instance, the gun boasts an elegant loaded chamber indicator… that can only be viewed by looking directly down the slide from the muzzle end…). But the author digresses…
When at rest, the recoil spring brings the slide and interlocked rear block fully forward; however, the breechface isn’t machined into the slide, and instead the slide presses a semi-free-floating bolt forward and into battery against the fixed barrel, which is integral to the frame. The rear of the bolt includes a flapper lever, that when in battery becomes wedged into the rear of the slide; this in turn cams the rear of the bolt down and wedges it into an angled locking surface in the frame. At the point of firing, recoil energy attempts to blow the bolt rearward, but the bolt is already locked down into the frame by virtue of the camming action of the lever. Since it is wedged in place, the energy transfers partly through the locking surface and into the frame and shooters hand, and partly through the lever and into the slide. Once enough energy has transferred into the slide to overcome its inertia and the recoil spring, it begins to move rearward. At this point, the wedging action against the bolt is relieved, and a groove in the “ceiling” of the slide picks up an extension on the top of the bolt to ensure it is pulled up out of the frame’s locking shoulder, and drawn rearward with the slide.
The aforementioned Mr. McCollum has identified this as essentially physics “black magic” which seems an apt description. The question as to if the gun is a locked or delayed is somewhat arguable based the definitions the author has provided for each. The question would come down to the point in firing where the slide begins to move. Once the wedge is eliminated, does the force of recoil cause the slide to slip out of the angled cut in the frame, thus opening from the force within the chamber as a delayed action? Or once wedged downward and held under pressure, would the bolt remain so locked if not for the slide pulling it upwards and dragging it rearward, thus being opened by the external force of the slide yanking it along in a locked fashion? The manufacturer doesn’t clear this up at all; the manual calls the system a “delayed blow-back Locking System”, so that is no help. Ultimately, it would seem to be impossible to know for sure without some extensive testing that could permanently damage the gun, and is unlikely to be carried out by any of their honored owners… a sort of Schrodinger’s pistol scenario.
That all said, the author’s own ill-fated experience demonstrates that a significant amount of the firing energy is drained into the frame – enough to deform the locking surface quite severely if not hardened sufficiently. This also explains why both the slide and priming weight of the gun seem to be so light (in a sample size of one defective example admittedly), as the frame takes most of the brunt through the locking surface. This fact, combined with the manufacturer deeming the slide groove and bolt extension to be necessary enough to add, has tilted the author’s view toward calling the system locked, even if tenuously. Therefore, it has been included here in this essay.
John Peterson’s hesitation lock is another example of something easier to understand than to explain. It was used to great effect in the Remington 51 pistol, and to much more lackluster effect in the more recent Remington R51 reimagining. The author had intended to pick one of these up (the 51 that is) for further examination and collecting purposes, but alas, the woes of the world have rearranged some priorities.
The concept of the hesitation lock bares some similarity to the inertia locked design above, in that it doesn’t fully lock until recoil energy is applied, and the ultimate opening is accomplished by the transfer of inertia into the slide which then pulls the bolt out of lock. At rest the recoil spring around the non-moving barrel presses the slide forward. This interlinks with the bolt and pulls it forward into battery against the barrel; this position also lowers the tail of the bolt. When fired, recoil energy from within the chamber presses the bolt rearward, which in turn presses the slide rearward against the recoil spring. In this state, the gun is operating in a direct blow back manner; however, this changes when after only a short distance, the downward hanging tail of the bolt strikes a locking surface on the frame. This locks the gun, albeit in a slightly ajar position. The inertia already imparted to the slide allows it to continue rearward on its own, and as it does so, it cams the rear of the bolt upwards and out of lock, thus freeing the action to fully open and cycle.
The outstanding question that the internet video commentary on the gun has left the author in wonder about, has to do with the hesitation period between when the gun actually locks and unlocks. During this phase the rear of the case is presumably partially withdrawn from the chamber. Does this, as some have suggested allow some gas and pressure to vent around the case and into the action similar to slowly cracking open a bottle of pop (or soda or coke or whatever the reader may call it) and allowing the excess carbonation to bleed off safely? Or does the pressure keep the casing form fitted to the chamber, avoiding a case rupture by simply slowing the initial opening via the blow back style mechanics? And how does this compare to the very svelte prototype Remington M53 .45acp version on display in the Springfield, Missouri NRA Museum? More research may be needed… again, funds will be accepted.
Of the plethora of semi-automatic handguns that have been designed and marketed, they virtually all have one thing in common: they feed from a magazine through a single chamber that cycles open and closed during operation. But a notable exception to this are semi-automatic guns with multiple chambers… six chambers, in fact… semi-automatic revolvers.
The author is aware of two examples of these. The British Webley-Fosbery is the earlier example from the early 1900s, with the Italian Mateba 6 Unica being far more recent and apparently available again at the time of this writing. Both guns work in essentially the same fashion, splitting the frame into upper and lower portions, with the upper reciprocating against a recoil spring over top of the lower. As the opposing recoil and spring forces cycle the barrel, cylinder, and upper frame back and forth, their interaction with the comparatively immobile lower frame ratchets the cylinder to the next position and re-cocks the hammer for the next single action shot. The Webley accomplishes this via a zig-zag cam track carved on the exterior of the cylinder, while the Mateba utilizes a more common pawl design to rotate the cylinder from the rear.
The question here is where these anomalies fit into the phylogenetic tree. Revolvers do technically keep the chamber, barrel, and breechface locked together in alignment throughout all of firing. The automatic rotation of the cylinder (the action making them semi-automatic) is facilitated by the normal force of the lower frame, thus further meeting the previous definitions for locking set above. And finally, the cycling (rotation) of the action (cylinder) is driven by recoil energy. These three things, while unconventionally combined, would seem to appropriately place these handguns here in the lineup.
Rounding out the list of less common locked breech, recoil operated pistols, is the category of long recoil systems. In these systems, when fired, the barrel and breechface remain locked together as they both move rearward under recoil force. They remain locked until they reach the full rearward extent of travel, with a distance moved of greater than the length of the cartridge. At this point a catch is tripped by components within the comparatively immobile frame, and the action unlocks allowing the barrel to return forward into position under its own spring pressure. As the barrel moves forward, the bolt is caught in the rear position, where it retains a grip on the spent casing. Once the barrel clears the casing, the empty shell is expelled from the gun, the bolt is tripped to return forward into battery behind the barrel under the power of its own separate recoil spring, and in so doing it strips and loads another cartridge into the chamber. Simple.
These systems have one very notable advantage, in that the breech remains closed for a comparatively very long time, thus ensuring the pressure has dropped well into the safety margin before opening. This feature makes a bit more sense in the higher pressure world of rifle and shotgun cartridges, and as such most long recoil designs were focused here, as opposed to the relatively low pressures of handguns. Even at that, the complexity of long recoil systems fell out of favor in the first half of the 20th century, and few modern designs still use these designs.
Nevertheless, a few attempts have been made at creating long recoil operated handguns, only one of which found moderate success – the Frommer Stop. The operation of this odd looking little gun is as described above, but it pairs this with a rotating bolt head design of locking system. The force of the recoil drives back both bolt and barrel, but as the barrel begins to move forward again, it pulls on the bolt head it is locked to. As the bolt head is pulled out of the temporarily captive bolt carrier, it is drawn along a cam track in the bolt that rotates the bolt head and unlocks the gun. To the author’s knowledge (and collecting relief) this is the lock up used in the handful of other long recoil pistol designs as well.
If long recoil includes the barrel travelling the “long” distance of just more than the entire cartridge length, the reader can likely guess that short recoil would be defined by the barrel travelling a shorter distance before decoupling from the breechface. This would be accurate. These systems usually only see the barrel remain locked to the breechface for a fraction of the distance of long recoil systems before the lock is opened and the barrel is arrested in its movement, thus allowing the opening and cycling of the action. One can see how this system would open faster and therefore be less favorable to long barreled guns where the pressure remains higher longer. But for handguns, it proved a winning concept, leading to the most prolific and commonplace of modern pistol designs. Of these, the author has identified no less than seven categories of locking mechanism, with a few sub-categories as well.
These seven can be divided into roughly two design philosophies – guns that consist of a separate barrel and integrated slide/breechface, and guns that consist of an integrated barrel/slide and separate bolt. The author will attempt to keep these as segregated as much as possible, but the sheer variability in this class of guns does make it a bit of a challenge.
Toggle Locked (barrel/slide & bolt)
Of the menagerie of short recoil, locked breech pistols, one of the earliest successful designs was the toggle locked system found most famously in the Luger. Toggle locked systems in general can be traced back from the Luger into both the Maxim machine gun, the entire line of early Volcanic/Henry/Winchester designs (pre-Browning of course), and even back into some small scale breech loading cap and ball offerings. Nevertheless, the Luger remains the high water mark for the concept in a semi-automatic format, with subsequent designs falling swiftly victim to the shortcomings of the system – especially expense in manufacturing.
The author’s Luger is a wonderful 1906 “American Eagle” US import gun, that he could go on about regarding its matching numbers and handling characteristics compared to the later P-08 modifications, and… Anyway. The toggle locked system of the Luger (and all such systems in general) work much like a human knee joint. When extended in a straight line, the bones lock into place such that the body can be supported with little fear of collapse. However, once bent, the knee can fold far more readily under the exertion of external force.
Toggle lock systems work similarly, with the force of recoil driving the bolt rearward and into a straight-line linkage. In the Luger, the back end of that linkage is pinned to the slide and barrel assembly, so they are drawn rearward as well. This lock is interrupted after a short distance by normal force of the frame; the iconic round toggles on the linkage strike the upward angled portion of the frame which thrusts them upward. This breaks the lock, and as the lug under the front end of the slide then strikes the back of its corresponding channel in the frame, the bolt is allowed to continue rearward the rest of the way as the linkage folds upward behind it against spring tension. Once the bolt hits its rearward limit of travel (thus ejecting the spent case) the mainspring in the grip begins to pull the linkage back down and into a straight line, which in turn pushes the bolt forward until it chambers a round fully and shoves the slide back forward and into battery.
All in all, the Luger’s toggle locked system stands out from the others in that the lockup does not include interlocking lugs marrying the pieces together. Instead it is locked by the physics of the recoil against specifically angled and tightly milled components. Whilst very cool, this would ultimately prove far more expensive and labor intensive to produce than following designs, and thus toggle locking, at least in semi-automatic systems, has been relegated to the past.
Rotating Bolt Locked (barrel/slide & bolt)
Rotating bolts are an exceptionally common method of locking a gun, and have been used regularly in designs since bolt action rifles became a “thing”. Though less common, they still frequently show up paired to various operating systems in handguns. The aforementioned long-stroke gas operated Desert Eagle utilizes an AR style rotating bolt. The Frommer Stop pairs a rotating bolt with its long recoil action. But the author is only aware of one gun that utilizes a rotating bolt paired with a short recoil action. The AutoMag.
When at rest, the massive gun’s dual recoil springs pull the bolt forward and into lock and battery with the barrel. Upon firing, the recoil energy drives both rearward, but almost immediately the AR style bolt begins to rotate. This is facilitated by the normal force of a transverse lug that extends through the frame support that retains the bolt, and through an open cam track in the bolt itself. Shortly after fully rotating out of the locked position, the barrel/slide assembly strikes its rearward extent against the frame. This impact also engages an angled lever under the barrel that then strikes one of the locking lugs on the bolt head with some additional force to ensure it continues accelerating backwards free of the barrel. The bolt continues rearward, ejects the spent case, cocks the hammer, returns forward under spring pressure, chambers a new round, and cams back into lock and battery with the barrel/slide.
Roller Locked (barrel & slide with breechface)
Visually a roller locked gun appears to be very similar to a roller delayed gun, and indeed in construction and concept the two mechanisms are not unrelated. The difference, of course, can be identified in light of the initial definitions made above. Whereas roller delayed guns are opened purely under the recoil force within the chamber overcoming mechanical disadvantages, a roller locked gun remains locked until acted upon by the normal force of the frame and locking piece.
And thus, comes the author’s CZ-52. The bottom of the chamber end of the barrel is milled out to house two vertical rollers, and a locking piece. The locking piece consists of a rearward pointing wedge that rides between the rollers, and a forward mounted collar that slides over the barrel. When assembled, the locking piece mates snugly into a cutout in the frame that immobilizes it in relation to the barrel.
When at rest, the recoil spring drives the slide forward against the barrel, and pushes both into battery. This also wedges the rollers outward against the locking piece, and into their aligned cutouts in the slide. At this point, the rollers are not resting on the locking piece’s angled surface that they could pinch out of place like in a roller delayed system; rather they are held outward by the flat sides of the locking piece, keeping them unable to move out of lock at all. When fired the coupled barrel and slide move rearward together for a short distance before the barrel strikes its stopping surface on the frame. During this movement, the locking piece remains immobilized in the frame such that the by the time the barrel stops moving, the rollers have cleared the flats of the locking piece and are allowed to roll inward, unlocking the gun. This frees the slide to continue rearward and fully the cycle the action.
To the author’s knowledge, the CZ-52 is the only handgun to employ this system. As such, it sadly becomes very difficult to evaluate the qualities of the system, as they are overshadowed by the shortcomings of the other Soviet era design choices. The safety/decocker bounces sharply into the user’s thumb, and somehow the trigger also bounces uncomfortably forward into the shooter’s finger once fired. These paired with generally rough edges and next to no polishing anywhere make the gun, whilst mechanically and historically enthralling, practically unpleasurable to shoot.
Falling Barrel Locked (barrel & slide with breechface)
The locked breech systems described up to this point have all included some sort of mechanism (bolt head, toggle linkage, rollers, etc.) that have provided the locking surfaces; however, the next three designs feature the barrel itself acting as the locking mechanism.
The first design the author will here tackle, is the angled falling barrel of the Webley 1910 pistol. Whilst the external design looks very… elementary school, the internal function is much more interesting. When at rest, the barrel itself locks into the ejection port of the slide, as both are pressed forward and upward together. When fired, they both begin to move rearward together, but the chamber section of the barrel actually contains angled lugs on its sides that engage with cam tracks milled into the frame. Immediately upon moving rearward, these cam tracks begin to slide the barrel downward and back, thus after only a very short distance, pulling the chamber down out of lock with the slide, allowing the action to cycle as expected.
This design is notable for keeping the barrel perfectly horizontal whilst moving it downwards and out of the way, but even more so for the locking surface being the chamber portion of the barrel interfacing with the ejection port. This is so commonplace in modern pistol designs as to be considered the standard, yet the Webley & Scott Autoloading Pistol was the first to pioneer this idea.
Tilting Barrel Locked (barrel & slide with breechface)
Quite similar in design to the Webley is a design that needs no introduction amongst even the most novice of gun enthusiasts – the tilting barrel lock. After forging an appropriately famed and lauded career in revolutionary designs for single shot rifles, lever actions, pump actions, gas and recoil operated autoloaders, and machine guns, one of the final golden eggs to be laid by the legendary John Moses Browning was the short recoil, tilting barrel action. It would become immortalized by the Colt 1911 pistol, and copied and modified so much as to become the definitive default and standard in modern locked breech pistol design. The author will here describe the lock found in his modern Springfield Armory GI-45 model of 1911, before identifying some common variations on the theme.
When at rest, the slide is pressed forward against the barrel and into battery. The barrel is horizontally aligned with the sights, and locked into the slide via a series of interlocking lugs and groves milled into the top of the chamber of the barrel, and the inside of the slide. When fired these groves keep the barrel and slide locked as they recoil together, but under the barrel there is a short linkage and pin attaching it to the frame. After a short distance, the linkage reaches a point where it begins to pull the breech end of the barrel downward. This continues until the barrel is pulled fully out of lock and stopped from travelling any further rearward. The slide is then freed to continue cycling, as it has enough wiggle room in and around the barrel bushing to allow the barrel to remain tilted out of the way. Upon closing, the breechface contacts the barrel and carries it forward along the arc determined by the linkage, and back into battery and lock.
While the 1911 remains a viable and popular pistol to this day, various improvements to the design have been made in the intervening years. Guns such as the ubiquitous Glock, and the author’s own Hudson H9 use the Webley locking system, with the barrel tilting upwards into lock between the chamber and ejection port. Additionally, these and others have moved away from the multiplicity of small pieces involved in the 1911s camming linkage, and instead have opted for using the far simpler interaction of angled surfaces milled into the barrel and frame. But no matter the combination of features, the historical significance of the tilting barrel design cannot be overstated.
Rotating Barrel Locked (barrel & slide with breechface)
While similar to the previous two designs by virtue of using a locking lug integral to the barrel, this design returns to concept of using rotation to lock and unlock the gun; this time via rotation of the entire barrel. This idea has been touched on previously with the likes of the Savage 1907, in which the rotation of the barrel was closed on an angled surface, and cammed to open through the force of recoil alone. Rotating barrels in locked systems, however, utilize an actual locking lug that cannot be shoved out of the way until cammed aside by external force. Additionally, the Savage delaying mechanism utilizes the innate rotational force generated on the barrel via its rifling to oppose the rotation needed to open the action; in the example below, the unlocking occurs counterclockwise and in the same direction as the internal rotational force, thus using that energy to aid in opening vs. fighting it.
This design concept has actually been in existence since the earliest days of autoloading designs, and has seen implementation in many early Roth and Steyr pistols, etc. Despite fading in favor under the likes of other designs like the tilting barrel, there are still notable modern guns that also utilize the design. The Boberg/Bond Arms bullpup pistols pair a rotating bolt with a complex mechanism that loads the chamber from behind the magazine, but the author has yet to obtain one of these. Instead his collection contains the far more polished and proven Beretta PX4 Storm.
When at rest, the PX4’s slide and barrel are pressed forward and into battery by the recoil spring (as expected by now). The locking surface holding these two together are two lugs extending from the chamber of the barrel; one visibly locks against the ejection port of the slide, while the other locks into a similar surface milled into the opposite side of the slide. The barrel is held in this orientation by a camming block that is locked into the frame. When fired, the recoil pressing against the breechface of the slide draws both the slide and locked barrel back, but in so doing the interaction between the normal force of the camming lug in the block and the moving cam track milled into the barrel begins to rotate the barrel as it travels. Eventually the barrel rotates until the locking lugs disengage their respective surfaces in the slide, and the barrel is caught and held by the camming block while the slide continues to cycle (also as expected).
Beretta heralds this design as being lower recoil than other designs, as a portion of the recoil energy is converted to rotational energy within the barrel. While the author does find the gun generally pleasant to manipulate and fire, and certainly far more accurate than he can is, the difference in recoil impulse is questionable. A more scientific comparison will at some point be in order.
Locking Block Systems
Competing neck and neck with the toggle locked system for oldest successful pistol locking system, is the varied world of locking block systems. These take many forms, but the core concept is simple – the barrel and breechface (be it in a slide or a bolt) are locked together by an external block that itself must be dropped, tilted, lifted, or otherwise moved to decouple the action and allow it to open. The author owns two such historical designs in the form of a C96 “Broomhandle” Mauser, and a Walther P-38, but many other variations on this theme exist, further complicating his collecting needs and financial constraints. He will attempt to identify a few major variations as follows.
Barrel/Slide locked to a Bolt by a centrally located locking block: This design is personified by the C96 Mauser, in which the barrel and slide are a single monolithic piece that houses a sliding bolt. At rest, the bolt is locked into the slide by a block under the slide assembly. This block pivots on a protrusion from the slide assembly, and tilts up into locking recesses milled into the bolt. It also includes its own protrusion that sticks down into the clockwork locking mechanism frame below. Upon firing the entire upper assembly moves rearward a bit against the mainspring, taking with it the locking block. However, the protruding connection between the locking block and the comparatively immobile locking frame, creates a levering action against the slide that tilts the locking block down and disengages it from the bolt. Once levered down, the normal force of the shooter, lower frame, and locking frame, is translated through the block and into the slide, and it is stopped from further rearward travel, allowing the bolt to open and cycle before reversing the entire process to close. Nobody ever claimed these guns were simple… just super cool.
Barrel/Slide locked to a Bolt by a rear locking lug: At approximately the same time that Mauser was developing their complex C96, the Mannlicher 1896 was under development with a similar form factor, but differing lock up. This gun uses a slide/barrel assembly with an internal bolt and a pivoting locking piece pinned to the lower rear end of the slide. When at rest, the slide/barrel assembly is pressed forward, and the front portion of the locking block is wedged upward by a portion of the lower trigger group that is affixed firmly to the frame. This upward wedging action presses it into the back of the bolt and locks the bolt closed within the slide. Upon firing the entire slide and contents begin to move back a short distance before the locking block moves out of contact with the lower wedging surface, and is allowed to swing down and out of the way of the bolt so it can cycle.
The author does not have access to one of these beyond photos and videos thereof, so he is unsure of the exact force responsible for opening the action. Drawings appear to indicate that the locking block is angled such that it would wedge between the locking surfaces on the bolt and frame/trigger group so long as forward pressure was extant. Once pushed rearward, the locking block may simply drop out of the way via gravity, or it may be shoved down by the angled locking surface of the bolt itself, or some combination. Per the initial definitions set forth above, this may consist more of a delaying feature then a locking feature, but as the author lacks better resources to confirm or deny his suspicions, he will let stand the rulings of so many others on the subject… for now…
Barrel/Slide locked to a Bolt by a locking collar: Another approach to using a locking block is by using a vertically travelling locking collar that sleeves the bolt as in a Bergmann Bayard 1910/22. At first glance the bolt of this pistol looks very reminiscent of the C96 Mauser including the two locking cuts on the bottom. In fact, the entire gun bares a similarity to the C96, but with the exception of the Astra redesigns of the C96, the Bergmann Bayard could well be considered the most product improved and end of the line for that form factor of pistol. This is evident in its far simpler design.
The locking block in this design consists of a square collar that slips over the bolt and rides vertically in cut outs in the slide. When the collar is pressed upward, it engages with the locking cuts in the bottom of the bolt, thus locking the bolt into the slide. When the collar slips down, the bolt is disengaged from the collar and slide, allowing it to reciprocate freely. To control the up and down movement of the locking collar, it includes two angled surfaces, one across the bottom front edge and one across the top rear edge. When at rest, the locking collar is pressed forward by slide and its bottom front edge is wedged upward by a corresponding angle in the lower portion of the frame. Upon firing, the bolt, collar, and slide recoil a short distance, back into an alcove created within the frame. The top of this alcove has and angled edge that engages with the top rear edge of the collar and pushes it down and out of lock. The slide and collar are then stopped from further travel by the frame, while the bolt continues rearward to complete its cycle.
Barrel/Slide locked to a Bolt by a partial locking collar, and a using a bolt accelerator: In a similar design to the Bergmann, but with a form factor more along the lines of the Luger, comes the Lahti L35. The L35 utilizes a similar locking collar to the Bergman, except it is open on the bottom and engages with the bolt on the top. The collar has two cams on either side of the bottom of the piece. When at rest, corresponding cutouts in the frame pull these cams downward, slipping the collar down within the slide and locking it into the bolt. As the bolt, collar, and slide recoil, the frame cams the bottom of the collar upwards as the slide hits its rearward extent, thus disengaging it from the bolt and allowing the gun to cycle freely. At this point an accelerator lever in the front of the slide (not unlike the much later designed AutoMag) is engaged by the frame and strikes the bolt with an additional dose of momentum. This addition is credited to the harsh Finnish conditions in which the gun was designed to operate; the idea being that in the commonly cold and dirty conditions of military exercises in the region, the bolt would expend too much of its momentum unlocking to reliably finish cycling, and thus need an additional shove.
Barrel with affixed block locked into a Slide: Of all of the pistol locking block options, probably the most enduring and successful is the design incorporated into the Walther P-38 (and related model designations). This system includes a relatively modern slide and barrel over frame arrangement, with the locking block of a tilting variety and affixed to the barrel. At rest, the slide and barrel are pressed forward together, and the frame presses the locking block upward such that its two lugs extend upward and engage matching cutouts in the slide. When fired the slide pulls rearward on these lugs and hauls the barrel back with it for a short while. This is stopped when a downward extension of the barrel strikes the frame. Extending through this barrel extension is a small plunger that gets depressed by the collision of barrel and frame. This plunger extends forward and cams the locking block down and out of engagement with the slide, thus freeing the slide to cycle as expected. This system is certainly one of the simpler designs in terms of part count, disassembly, and overall handling, and therefore it is no surprise that it was adapted with surprising little variation into the long serving Beretta 92/M9 pistol family.