The Safety Dance (With Apologies to Men Without Hats)

Things like this make me CRAZY:

She peered around the edge of the doorway.  Harry the Horse and Big Julie were huddled over the table, staring at the cards in their fists, blissfully unaware that death stood on the other side of the door jamb.  She took a moment, forcing herself to center, controlling her breathing, achieving an inner calm.  In a few moments, nerves and worry were gone, and all that remained was a cold, steely determination.  She reached back and curled her fingers around the butt of the Smith & Wesson Model 686 .357 Magnum revolver holstered behind her right hip.  With a practiced tug, she pulled it from the holster, flipped off the safety….

Grrrrr! <Said through gritted teeth> "Revolvers. Don’t. Have. Safeties."*

That’s usually the place where I put the book down and walk away or fight the temptation to run screaming from the  movie, frustrated by the lack of accuracy. Since I hate to walk away from a perfectly good book, a general discussion of the mechanical safety mechanisms found on handguns might be useful for those of you involved with writing books or producing movies.  Especially if you have curmudgeons like me in your audience.

Manual Safety on a Browning Hi-Power

Let’s be clear from the start:  An external, manual “safety,” or safety catch is a mechanical mechanism that is designed to reduce the likelihood of an unintentional or accidental discharge of a firearm.  It is usually a switch that, when engaged, prevents the firearm from discharging when the trigger is pulled.  Typically, the switch interposes a mechanical block that prevents either the trigger, the sear (the intermediary component acted upon by the trigger that holds and/or releases the firing mechanism) or the firing mechanism itself from moving.  Ideally, the safety must never interfere with the intentional discharge of the firearm.

Risky Business

Safeties are about managing risk and probability, not providing mechanical absolutes.  Mechanical devices can, and routinely do, fail.  Certainty can be achieved only by never loading the firearm.  Importantly, in cases where other functional attributes of the firearm manage the risk of unintentional discharge to an acceptable level, external/manual safeties are either redundant or omitted from the design entirely.

To understand safeties, it is necessary to understand what comprises the “risk condition” in a firearm.  This, in turn, requires a bit of knowledge as to how firearms and ammunition work.  

Bang for the Buck

Cartridge Components

Ammunition functions on the principle that the controlled burning of a given amount of solid propellant will cause the generation of rapidly expanding combustion gases, and that the expansion of these gases will force a projectile down the barrel and toward the target.  Reliable ignition of the propellant is ensured through the use of a chemical primer compound.  The primer compound is impact sensitive, meaning that it detonates when struck sharply, producing a short, intensely hot flame. (Think of the cap guns you had when you were a kid.)  It is this flame that ignites the propellant.

A (Spring) Loaded Question

Note firing pin and hammer

The role of the firearm’s firing mechanism is to consistently transfer kinetic energy to the primer compound.  Typically, this is done by causing a steel firing pin to strike the base of a cartridge, where the primer is located.  The motive energy that moves the steel pin is stored in a compressed spring (the “mainspring”).  The spring is held under compression by a mechanical block until it is released by the trigger to either act directly on the firing pin or to forcefully rotate a hammer, which strikes the firing pin, causing it to move rapidly forward.

These basic mechanics result in the existence of three distinct operating modes for a firearm:

• Rest, when mainspring is relaxed and there is no energy stored to propel the firing pin;
• Ready, when the mainspring is compressed, storing energy to propel the firing pin; and
• Firing, the instant when the mainspring is released, expending energy and propelling the firing pin into the primer at the base of the cartridge.

Risk Model for Unintentional Discharge

Of the three, the risk space for unintentional discharge settles by a wide margin (some studies say as much as 9:1) in the Ready mode.

Safeties then, are a means of mitigating the risks attendant to having a compressed spring behind a firing mechanism that is restrained only by a controlled release mechanism (i.e., the trigger/sear).

Options

Safety on a Luger Pistol

The manual safety, like those found on a German P.08 Luger or an American M1911A1 pistol is one option to mitigate the risk of an unintentional discharge.  It is ideally suited for single action pistols where the Ready mode is a normal mode of carriage, where rapid employment not requiring manipulation of the breech mechanism is desired and where the pistol’s design precludes bringing it into operation without first manually compressing the mainspring.  

Colt Single Action Army.  No safety.

However, the manual safety is only one mitigation to the risk problem, and incidentally, not the first.  The original mitigation is found on single action revolvers like the Colt Single Action Army, was simply never to cock the pistol (and therefore compress the mainspring) unless it was desired to immediately bring the pistol into action.  This is a training mitigation (or, as those of us on the military end of the spectrum like to say a “tactics, techniques and procedures” (TTP) fix).  While it may not directly answer the mail, it does make for a mechanically simpler and therefore more robust design.

The most effective option, from a risk mitigation perspective, was to all but eliminate the need for a Ready mode.  If the trigger can be made to perform TWO functions; that is, both cocking the firing mechanism (compressing the mainspring) *AND* releasing the firing to hit the primer, there is no need to secure the firing mechanism against the force of the compressed mainspring.  Thus was born the double action pistol.

Double action S&W M60. No safety

On a double action pistol, the amount of force that needs to be applied to the trigger to overcome both the mainspring weight and the mechanical interplay of the fire control components is significant; between eleven and fifteen pounds of force is required to overcome the mechanical disadvantage and fire the pistol.  The possibility of this amount of force being applied accidentally is remote, and as a result there are almost no double action revolvers on the market today that have an external mechanical safety.  (As a note, most modern double action revolvers feature a number of internal, passive safety mechanisms intended to minimize the chances of a discharge should the firearm be inadvertently dropped.)

FN P45. That's a decocker, not a safety.

The lack of an external, manual safety is also a feature of modern double action semi-automatic pistols, for much the same reasons discussed with respect to revolvers.  However, double action semi-automatic pistols present a somewhat different risk mitigation challenge than double action revolvers.  Specifically, at the completion of a firing cycle that has not exhausted the ammunition supply, a double action revolver returns to the Rest mode.  A double action semi-automatic pistol on the other hand, returns to the Ready mode (Glocks and “Double Action Only” pistols are exceptions to this rule).  To allow the pistol to be safely returned to the Rest mode, many double action pistols have a decocking mechanism.  The decocker, while having the external appearance of a manual safety, performs an entirely different function.  It allows the mainspring to be safely decompressed without discharging the pistol.  As an aside some pistols, notably James Bond’s Walther PPK, combine the functions of safety and decocker in a single lever. (As a note, most modern double action pistols feature a number of internal, passive safety mechanisms intended to minimize the chances of a discharge should the firearm be inadvertently dropped.)

Walther PPK. Combined decocker and safety.

Conclusion

In sum, the manual external safety is a device intended to mitigate the risks attendant to carrying a cocked pistol with a round of ammunition ready.  The following is a quick cheat sheet that might be useful when arming your characters:

• Single Action Revolvers (think “cowboy guns”): No external safety
• Double Action Revolvers (think “police pistols from the 30s - 70s”):  No external safety
• Single Action Semi-Automatic Pistols (think “GI .45s”):  External manual safety
• Double Action Semi-Automatic Pistols (think modern military pistols):  External manual decocker
• Glocks: No external safety

 *For every rule, there are, of course, exceptions.  The German Model 1879 Reichsrevolver, the Webley-Fosbery Automatic Revolver and the Mateba Model 6 Unica Autorevolver all have safeties.  They’re also rare, obsolete or a combination thereof.  Then there are folks in the “can’t let well enough alone club” like  Tarnhelm Supply, who are always seeking to gild the lily.