Can one rig a revolver to guarantee that the only bullet in Russian Roulette is in the last chamber?

Question

We've got this criminal who likes to interrogate people via Russian Roulette.

While his captive watches, he empties an unremarkable-looking 6-chamber revolver, re-inserts a single bullet, spins the cylinder and slams it closed, then points it at the captive's face. Then he asks his questions, pulling the trigger each time he's unsatisfied by the interogatee's reply.

Because he does not re-spin the cylinder between trigger-pulls, the chances increase each time that the next chamber will hold the bullet. Thus, each successive question conveys more threat than the last. Our criminal knows this, and wants to maximize the number of questions he can ask. He also wants to give himself the option to end each interrogation without killing his captive.

So, what he think he needs is a special pistol that somehow guarantees that the cylinder will slam into position such that the bullet is in position farthest from the firing position.

What he needs:

it should not be obvious to onlookers that this pistol is unusual in any way; ideally, it would pass casual inspection by a civilian who knows what Hollywood knows about guns
if the pistol has a real bullet in every chamber, it must be capable of firing each like a normal pistol, because this is the same gun he uses as his regular sidearm
he must be able to perform his prep ceremony, because it's a key part of the intimidation, and he enjoys doing it
the pistol must really fire the bullet when it comes around -- he often does execute the captive using this weapon, and he doesn't want his goons to know the game is rigged so their own reactions don't give the game away
must be doable for no more than $100,000 US
setting is real-world 1990s; no magic, no aliens, no capes, no super-tech

I'm not married to the idea that the cylinder has exactly 6 cylinders.

I need to understand the details of your idea clearly enough that I can describe them in the story when it comes time to reveal to the reader how this criminal arranged this, including what kinds of tradespeople he needed to hire (and, later, murder).

Post-selection update to address a persistent topic in the comments.

Using blanks is unacceptable for an obvious reason: firing a blank makes a detonation sound that every observer will notice. Firing a blank is not indistinguishable from pulling the trigger when the chamber is empty.

Do note that your revolver needs to be a special case anyway. As far as I can tell it's normal that you can see the actual bullets from the front of the gun, making it hilarious for the interrogated. If he/she can see the actual bullet when it's aimed at them it kind of eliminates nearly all excitement. — Trioxidane, Apr 22 '22 at 13:02
seems like we have to assume that nobody talks, otherwise somebody is going to figure it out eventually, whether it's due to the henchmen noticing it's always the 6th shot, or survivors who tell each other how many empties were "discharged". — Michael, Apr 22 '22 at 18:25
@Trioxidane That was my first thought, but you have to have a good angle of view to see the ammunition. The bad guy could press the revolver into the victim's head at an angle where they can feel it, hear it, and even see it, but not see it well enough to spot an empty chamber. — David K, Apr 23 '22 at 00:53
Frame challenge: what you describe is fairly similar in essence to what real-world magicians do. One way is to rig the gun, another is to up your talking game to the point where all eyes are on you, you intentionally fiddle with the gun in plain side, slowly clicking the barrel, menacingly looking at the victim in the process... All while making sure the bullet is where he knows it is and where he wants it. Almost the same but with more time and possible tells (adding more resistance to a spot underneath a specific slot shouldn't be too hard to do and feel while spinning the barrel slowly). — Lodinn, Apr 23 '22 at 19:50
If it matters that much, why use a revolver? Why not use an automatic with duds or blanks and one live round at the end of the magazine?
Else, why get hung up on all that detail? Either on the details in the exposition, or on the potential mechanics of any solution?

Given that what you describe won't be impossible, however difficult, why not just write the scenario without using technical details… just as if this was an ordinary pistol in an ordinary game or Russian roulette, you wouldn't even think about those details? — Robbie Goodwin, Apr 24 '22 at 01:42
@RobbieGoodwin Aside from the awkwardness of having to fiddle with the gun to cycle the duds out of a semi-automatic pistol, or the likely injuries to your victims by firing blanks at them at close range, everyone is going to know that you know where the live round is, because there's no way to "spin" a loaded magazine to put the live round in a random position. — David K, Apr 24 '22 at 04:16
For many revolvers, you can see the rims of the loaded cartridges from the rear after the gun is closed. So if the live round isn't where it should be, the bad guy at least will know and can arrange a diversion if needed. — David K, Apr 24 '22 at 04:23
@DavidK Of course everyone is going to know that you know where the live round is and please remember, this isn't real Russian Roulette, it's criminal brutality.
Do you think the fact that you know and the victim doesn't, makes things better, or worse for the poor victim?

Given the stakes, who cares if the blanks burn or blind the victim? — Robbie Goodwin, Apr 24 '22 at 17:45
@RobbieGoodwin If you put the gun up against the victim's head like in regular Russian Roulette, you'll likely kill them with a blank. You almost might as well use live rounds in that case. If instead you shoot from a few feet away then it's physical torture instead of psychological torture. The advantage of the revolver is that (at least with some models) you can spin the cylinder before slamming the action shut, so there's at least an appearance of randomness in the location of the live round. It makes the bad guy seem a little crazier and less calculating. — David K, Apr 24 '22 at 17:52
@RobbieGoodwin Not my story, not my rules. I'll leave it to OP to digest all this. Maybe they'll take your idea. You could write it up as an answer. — David K, Apr 24 '22 at 18:46
@DavidK You might indeed kill the victim with a blank and so what? Where is it written that the pistol has to be put against the poor victim's head? How many other rules would you like to add? — Robbie Goodwin, Apr 26 '22 at 23:26

DWKraus · Answer 1 · 2022-04-22T00:40:48.283

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Two Identical Guns:

Your criminal has a matched set. One is pre-loaded to be only in the last chamber OR just empty (and concealed out of sight of the victim). The criminal does his whole show, steps behind the victim, does a quick swap for the identical gun, and then plays Russian Roulette. Only there's no danger of accidentally killing the victim, and even after 6 shots, they're still available to torture later. OR play Russian roulette with the original spun gun for bonus questions.

This also opens up possibilities for head games. "Answer truthfully and I'll play the next round. Lie or don't, and you play." It suggests an almost Joker-esque kind of crazy that really makes you look disbalanced. But since the game is rigged, why not?

edited Apr 22 '22 at 00:40

answered Apr 22 '22 at 00:35

DWKraus

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Best answer. Obviously the victim is tie to a chair and cannot see behind them. – Daron Apr 22 '22 at 13:09
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Even if the victim knows about this trick, the victim has no way of knowing if the criminal did it this time. Or maybe the criminal is intentionally placing the bullet on the first shot in cases where he doesn't actually want to ask any questions but does want to prove a point to his audience. So many opportunities for mind games and story hooks with this approach! – Brian Apr 22 '22 at 13:15

Trish · Accepted Answer · 2022-04-23T17:51:04.777

Magnets

A simple pair of magnets on the cylinder is enough to give it a vastly favored resting position, and also allows verification of the preparation.

The frame gets one magnet on the top strap, and one chamber gets a magnet inset on the corresponding position of the chamber. This chamber is also marked on the back, so that it is well known which chamber is the rigged one. To preserve the gun's function long-term, the cylinder is not slammed in but loaded the proper way. Now, our operator was careful with the choice of a revolver or did a minor modification: This revolver, when put in half cock, allows to spin the cylinder.

This is actually pretty simple: if the hammer moves back and the trigger tilts just a little, the block many revolvers have will get out of the way. Now only the hand that makes the revolver spin in the first place pushes the cylinder a little bit and it can spin in one direction. The hand getting pushed back by the wedges on the back of the cylinder makes the sound.

While free-spinning, whenever the magnets pass over one another, the magnets will slow the chamber down extra. For added dramatic effect, after the spinning, our handler might keep the gun at halfcock and rotate the cylinder by pressing it against his forearm a little. By turning the freely spinnable cylinder by hand, the attraction between the magnets will make that chamber that they want to line up at the top noticeable, allowing them to verifiably get the revolver rigged for the questioning. The cartridge is now in the top chamber.

At the first pull of the trigger (for which in some models the hammer needs to be lowered from halfcock to the rebound position first) or by going into full cock by drawing back the hammer, the cylinder rotates by one position. Since the top chamber ("6") was loaded, now the first chamber to be fired presents itself as an empty chamber, lines up with the barrel and hammer, and the handler will dryfire the revolver 5 times from chambers 1 to 5 before chamber 6 will go off.

score 24 · Answer 3 · answered Apr 22 '22 at 10:20

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Skill and Practice

Your criminal has spent hundreds of hours spinning the cylinder, slamming it in, and then checking which chamber the bullet is in without a victim present.

After all that practice, he is able to spin the cylinder with the same force, and stop it at the same moment each time, ensuring that the bullet is always in the same chamber.

Of course, if the pistol is replaced with a different one, or it isn't kept well maintained, his muscle memory will be off and he'll be back to square one.

answered Apr 22 '22 at 10:20

Tristan

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This is the most logical answer. With training you can get a coin to land whichever way you want. Well, at least most of the time. You just throw it with equal force every time, so it makes the same amount of turns in air. Not quite different to spinning a chamber - surely somebody could train to do the same spin every time. – VLAZ Apr 22 '22 at 11:36
spinning the cylinder seems much more controlled than flipping a coin too, there you'd have factors like wind, or air pressure changing things, whereas the cylinder of the revolver shouldn't be affected by environmental factors except in the extreme – Tristan Apr 22 '22 at 12:55
Yep. Well, different guns will probably have different spins but still something who is used to spinning chambers can get used to quickly. Or they can just use the same gun. At any rate, yes - probably easier than spinning a coin. People can get used to do all sorts of stuff that involves controlling the force they apply. Juggling is another example. Overall: no need for complex explanation when it's something well within a normal human's capability. – VLAZ Apr 22 '22 at 13:06
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with faint marks on each cylinder, or at least one, the criminal could verify whether the drum was in the correct orientation, and if not, spin a second, third etc time, which could easily be played for tension. – Dewi Morgan Apr 22 '22 at 16:44
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This reminds me of the Penn & Teller "Fool Me" show where a guy actually did just this, only with (iirc) cards and not a gun. Sadly, he did not fool Penn & Teller. – Michael Apr 22 '22 at 18:28
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@Michael his name is Kostya Kimlat – infinitezero Apr 22 '22 at 21:41
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Just to state the obvious, there is no way to do this sufficiently reliably in any realistic scenario, since the consequence of failure is murder or suicide. Idiots have done this kind of crap in real life and killed themselves. Even if you were very skilled and could do this reliably 99% of the time, do it 100 times and one person will die, on average. So it's really only suitable for a criminal who doesn't mind killing the captive being a possible outcome. – windblade Apr 23 '22 at 08:53
@windblade the idiots who try this aren't generally dedicating themselves to hundreds of hours of dry runs where there is no-one being shot. This absolutely is within the realms of human ability with sufficient practice. It's just that it's not the sort of thing real world people are likely to put enough effort into practising – Tristan Apr 23 '22 at 12:56
This reminds me of the first (or second) Tarzan novel. The bad guy and two other guys need to pick one different coin out of three. The bad guy is a card sharp and can feel the different width of the unlucky coin. – user3653831 Apr 23 '22 at 17:03
@Tristan This is simply not true. Look at the history of the "bullet catch" trick. Magicians presumably spent large amounts of time practicing a considerably safer trick, and several of them were still shot on accident. It's an inevitable consequence of performing a "slightly" dangerous stunt over and over. The statistics catch up to you, and even a 0.1% chance failure eventually gets you. – windblade Apr 23 '22 at 22:57
@windblade the bullet-catch is not at all analogous. In the bullet catch, someone else has control of the gun and the various methods for performing the trick are vulnerable to mistakes or interference by that person. In this case, the gun is entirely in the control of the criminal. Additionally, unlike a bullet catch, you can do a dry run of this trick easily, quickly, and on your own. Just load the cylinder, spin it, close it, and note where the bullet is before repeating. There is no risk during practice, and you can practice for a huge number of iterations – Tristan Apr 24 '22 at 13:49
@windblade: I think windblade is right. If you look at sports where repeatable precision is the basis of the sport, like curling (getting the rock to stop at the right distance), people still miss shots by throwing the rock with too much or too little speed, even with sweepers looking at it and judging whether it's light or heavy. Top level curlers do practice many hours a week for years, and still miss shots. The human body just isn't that consistent. Some minor scratch on one slot in the cylinder you can feel with your fingers is basically necessary to confirm that you got it right. – Peter Cordes Apr 25 '22 at 00:45
@PeterCordes curling takes much more time for each run, and the conditions are more variable, plus you have the interaction between the different participants. Spinning the barrel of a revolver has extremely consistent conditions which is precisely why it, unlike many other feats, could reasonably be assured solely by practice – Tristan Apr 25 '22 at 08:51

DBS · Answer 4 · 2022-04-22T18:16:10.993

A safety and a fake cylinder

Keeping the "only the last shot fires" part simple, we can use a hammer-blocking safety with a subtle switch that can be changed at will by the criminal, allowing any shot to be the "live" shot. A hammer blocking safety will also allow the gun to "fire" while on safe, as the hammer will be released, giving the distinctive click, but will not impact the round and fire the weapon.

(Image from https://projects.nfstc.org)

To allow the ritual of emptying the gun, a cylinder with stacked rounds could be used. An outer circle of rounds (which can never actually be fired as they don't line up with the firing pin, but look great when emptied out for show) and a smaller inner circle of live rounds (which all remain loaded) could be hidden by the body of the gun.

A real (but extreme, rather than subtle) example of a multi-layered cylinder (in this version, they are all functional and visible, rather than one layer being entirely for show and one being functional but concealed):

(Image from http://www.douglas-self.com/)

This should allow the ritual with as many "live" rounds as the criminal desires, while keeping a fully loaded and ready to fire weapon at hand just in case they're interrupted mid interrogation.

Eh.... that gun you have has a hammer with 2 firing pins and fires the two rings - which are offset by half a cartridge - in change: if you fired inner ring first, the next shot will be outer ring and vice versa. — Trish, Apr 22 '22 at 17:40
@Trish True, that was simply an example of a multi-layered cylinder. In this fictitious idea, the inner and outer chambers would be aligned (to give the illusion the visible inactive outer ring was the only ring), but only the inner would fire (it wouldn't have multiple barrels like this real example does) — DBS, Apr 22 '22 at 18:01

Jasen · Answer 5 · 2022-04-24T09:30:28.110

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it's possible to arrange for the cylinder to always stop on the same chamber when spun, perhaps some hidden centrifugal mechanism that regulates the speed and activates a stopper when the speed gets low enough. this technology should be possible by a competent watchmaker-gunsmith at technology levels well before 1990s. $10,000 is an entry-level Rolex so it should come in under budget too.

If this chamber is marked in some inconspicuous way then it can be carefully loaded with the single round.

edited Apr 24 '22 at 09:30

answered Apr 22 '22 at 01:38

Jasen

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But a Rolex is a watch and not a gun. – Daron Apr 22 '22 at 16:24
Also a Rolex is sold many times, not just once – Hakaishin Apr 23 '22 at 09:38
It's also one tenth of the budget, – Jasen Apr 24 '22 at 09:31

Daron · Answer 6 · 2022-04-22T13:35:25.547

Heavy Bullet. Freely Spinning Cylinder.

Your victim has watched a lot of Hollywood movies. They know you can spin the cylinder of the revolver after you load it. It goes round and around and goes click click whirrrr. . . and means you are now at the end of Act 2 and ready to start shooting baddies.

So when the baddy loads one bullet, closes the cylinder and menacingly spins the cylinder, the victim is terrified.

You cannot do this with a real gun. They are designed that way on purpose for safety.

However the baddie is not worried about safety. He has modified the gun so it is possible. Last night he has opened it up and sandpapered down the safety cylinder or housing so it can spin and go whirrrr click click click.

They have also filled up one of the chambers with a lump of lead. With a free spinning barrel they can decide where the heavy bullet goes by whipping the wrist in the opposite direction. They put the heavy bullet in the last place and the real bullet in the second to last place.

The downside here is you only get five shots and not six. After using five shots you have to switch to threatening the victim with something more painful like a chair leg. This is not the end of the world, since you would rather not kill them with the revolver, and it is better for the mooks if you beat them to death the old fashioned way.

Also the "heavy gun" or the "five shot revolver" could be a clue somewhere else in the plot. It would also be a good story twist if the reader doesn't know about this trope, but half way through the plot the investigators point out real guns don't work that way.

Or maybe in the final scene the baddie accidentally fires his "lead bullet" and something bad happens.

Ninja'd. I would use a bullet itself as a weight and just hold revolver upside-down during spin (just make intimidation more teatrical with a lot of gun flipping, demonstrating, how bullet is inserted and so on, so it would coincidentally ends upside-down when it is time to spin). As revolvers turn to next chamber first, then fire, you will have actualt bullet it the last tried chamber. — Revolver_Ocelot, Apr 22 '22 at 13:31
In the first part of that video, before the timestamp you linked to, he shows several of those guns have barrels that will spin freely. There's no clicking sound but it does spin. — Jack Aidley, Apr 23 '22 at 09:32
@JackAidley They can spin freely when the gun is open. When it is closed they cannot spin. — Daron, Apr 23 '22 at 11:42
@JackAidley Wait a minute. If it is only possible to spin the cylinder when open, surely it's always possible to decide where the bullet goes, if you practice hard enough. After all you can see the bullet with your eyeballs. — Daron, Apr 23 '22 at 11:42
@Daron Understood on the first point, and yeah I guess it would be. That's quite a good solution actually. — Jack Aidley, Apr 23 '22 at 14:04

score 9 · Answer 7 · answered Apr 22 '22 at 10:50

A simple rolling pin which stops the cylinder when it catches the bullet.

You have a cylinder that can spin when the weapon is closed when the safety is on. You spin the cylinder once more when the weapon is closed. When closed a tiny rolling pin moves outwards and gives resistance to the bullet each time it passes. The cylinder axle also has a resistance, but the time it takes to slow the cylinder to a stop is less than the resistance the pin needs to finally stop the bullet. This ensures the bullet is always in the same position.

For extra "fun" you can let the victim spin the cylinder a couple of times when you want to buy yourself more questions, or to quickly ramp up the interrogation. You quickly aim and pull the trigger at the knees and hands, then respin it.

Why is this a better option than spinning with the gun open and then closing it? Because the victim might assume that the user is simply skilled and can time it. With a closed cylinder and letting the victim spin it you take that away and it looks more random.

Although I would add multiple rolling pins which you can activate or not when the gun is open. That way you can stop the bullet at any position, and your fellows wont be wondering why the gun always fires at exactly the last shot each time.

score 9 · Answer 8 · answered Apr 22 '22 at 21:37

Add a hammer block safety.

Revolvers such as the Heritage Rough Rider single shot revolver .22lr come with a hammer block safety. By engaging the safety, the trigger still releases the hammer but it never hits the firing pin because a bar is in the way (thus the name, hammer block safety). This would let the character use as many "fake" shots as they would like.

I use this mechanism when introducing people to shooting as it lets me get them all set up and then flip the safety off. That extra margin of safety is really nice when working with people who are brand new.

As a suggestion, if you live in the US or other area where personal ownership of firearms is legal, you can probably find someone who would be willing to take you shooting with these types of revolvers to give you a greater idea of how they work. If interested, reach out to a local gun store or two to see what options are available. They will probably be able to get you set up with someone who has some experience introducing people to firearms.

Nice first answer awesome3, I'd never heard of this. Please take our [tour] and refer to the [help] for guidance as to our ways. Enjoy worldbuilding. — Escaped dental patient., Apr 22 '22 at 21:43

score 8 · Answer 9 · answered Apr 22 '22 at 13:01

Noise Maker

As part of the pre-interrogation ritual, the killer loads the bullet, and then manually cycles the cylinder until the bullet is in the last chamber.

Now he pretends to spin the cylinder, while activating a hi-fidelity audio recording of a cylinder spinning. The cylinder would only spin for a second or two, so if he is theatrical enough with his hand motions, he can have the gun moving for the duration of the playback, and his victim will never see the gun clearly enough to realize it was a recording.

This could be even easier if the lighting is set up appropriately - e.g. a dark room with a bright light aimed towards the victim.

Amadeus · Answer 10 · 2022-04-25T15:57:24.637

Modify the barrel, mark a chamber. The cylinder can have an open ring (a groove) on the surface, but near one chamber there is a stop. Near the trigger, the holder can press up a small pin into the open groove, so the freely spinning cylinder moves, but it hits the stop and ... stops.

Let go of the pin, so the cylinder can move freely again. But now the same chamber is always at the top, and the bullet (in the chamber marked with an inconspicuous scratch) is next to it.

You can let the person watch you spin the cylinder faster than they can see, and watch you make a show of stopping it with your hand, without even looking.

But you stop it by raising that secret pin (or lever) the moment before your hand hits the cylinder; they won't even notice that, if the cylinder is concealed by your hand.

With practice, it looks like you can spin the cylinder and land in exactly the same place every time.

PS You can also put in a check: Another little scratch on the outside visible surface of the cylinder, which will also always be in the same place if the cylinder stopped correctly. Just to prevent accidents.

score 5 · Answer 11 · answered Apr 22 '22 at 18:58

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A fake bullet

It never goes off, so it doesn't matter which chamber it's in. And if in the end you really want to execute the guy, just open it up again and add a real bullet.

answered Apr 22 '22 at 18:58

Vilx-

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Technically it’s not russian roulette if you are not holding the gun, and it’s cheating if you look at the gun. But if you let them cheat, many revolvers have a closed-face barrel and you can’t see the rounds from the front. Otherwise the entire gamble would be futile because if they see the round at any point, they can just count how many pulls they have left. So, a bad guy who doesn’t intent to kill anyone simply doesn’t need a live round at all. – Vogon Poet Apr 22 '22 at 23:17

score 4 · Answer 12 · answered Apr 22 '22 at 14:40

Mark the cylinder.

Your baddie just puts a subtle mark on the cylinder corresponding to a specific firing position--some kind of mark that could be felt would be best, maybe something that would look accidental like a nick/scratch. Then he loads the bullet in a specific place in relation to the mark, spins the cylinder, and before slamming it closed he spins it a bit more until he can feel the mark is lined up correctly.

Now you know exactly where your bullet is in relation to the rest of the gun, so you can do a bunch of tricks depending on how you offset it when loading. For example, you can load the bullet 3 cylinders offset and have one of your confederates pretend to be another prisoner--ask them a question two times and have them "break" and tell you on the third time, then say something menacing like "Let's see how lucky you just were." and fire the third time at a wall--bang! Then you turn to the guy you really want to interrogate, do the whole loading trick again, and say, "So, how lucky do you feel?" (Or a more bloody version where the first person you interrogate is another actual prisoner who you don't care about and you make it so they actually get the bullet after only one or two tries.)

If your criminal has other skills like card sharping or other slight of hand tricks then this fits in particularly well.

score 1 · Answer 13 · answered Apr 23 '22 at 07:01

Sheer gunslinging mastery means they can spin the barrel so that the live chamber always lands where they want.
There is a subtle method that prevents the firing pin from striking the bullet when held a particular way. Could be the barrel gets off center enough that the strike misses the primer, a slide to change the trajectory of the firing pin so it does the same, or a small bar with a gap in it to allow the firing pin through when desired but block it otherwise.
Similar to above but the gun is modified so the barrel always catches on a particular chamber so that the bullet can be put in whichever order is wanted. A particularly clever manipulator might make it stop on a fixed barrel when spun one way but not the other so they can prove the gun is 'fair' beforehand.
The chambers on the sides are blocked from view from the front but not from the back, after all the one being interrogated is the only one who needs to have that info hidden. This does have the disadvantage of only letting you know when the bullet will fire, no choice on how many questions beforehand.

score 0 · Answer 14 · answered Apr 25 '22 at 17:12

So you're looking at the following scene, based on your premise:

Victim tied to a chair
Table in front of the victim
Criminal in chair across from table
Criminal unloads revolver on table
Criminal picks one unloaded round, places one in cylinder, spins it, closes cylinder, points it at victim's face while both are still seated
At no time does the gun leave the victim's view

Several things here, and I'm combining several comments: this setup prevents any easy gun switching or fake noisemakers and thus is more menacing. It also means the victim has a clear view of the firearm, and we have to assume the victim retains a clear head and is capable of noticing things.

First problem: with the majority of revolvers, it's possible to see from the front if something is in a cylinder. The only ones you can't see is the one right under the hammer (ie, in firing position) and its opposite, hidden by the frame. If the light is right, and it's a short barrel, you might even be able to see the bullet down the barrel.

To make this simple, the first thing you want to do is make sure that any light is, coming from behind the criminal (or above and behind), so you've got a bright light in the prisoner's eyes, making it impossible to see the fine details on the gun clearly. That should eliminate the problem of being able to see where the bullet is. You also make sure that the light is arranged so that when the prisoner is looking down at the table, they aren't forced to squint and thus can clearly see everything that's happening. That's important for the trick. You also want a dark, non reflective table top.

You've already stated the cylinder is spun when in the loading position, which is good, and then moved into firing position. So, you use a simple trick that requires a very slight modification to the gun. Have an index notch at the rear of the cylinder. Something small that would be hard to see from the front, even if you didn't have a bright light shining in your eyes. Human fingertips are extremely sensitive and can detect very small imperfections, so your index notch doesn't have to be very big.

Open the gun and dump the bullets, concealing the index notch, and load the bullet into the chamber in relation to the index which is the one you want to use. Looking down to load the bullet would be natural, so there'd be nothing suspicious to make sure you have the right one. Then, while looking at your victim menacingly, spin the cylinder until you can feel the index notch under the thumb of your left hand (assuming you are a righty and the cylinder swings out to the left). If you have to spin it a few times to get it, that's fine, just makes it more "random". Then, still not looking at the gun, as your left hand swings the cylinder closed, the index notch allows you to determine the cylinder orientation, and thus where the bullet is, namely the last chamber that would come under the hammer, whatever it is depending on the type of gun. As you swing it closed, again, without looking, you subtly rotate the cylinder into the proper position.

And you're good to go. When you raise the gun and point at at the prisoner's face, now they're looking into the light, and the shadows on the gun make nearly impossible for them to see the cylinders, and thus where the bullet is. After every trigger pull, you lower the gun and turn it slightly so they can't see the ends of the cylinders. This again conceals the location of the bullet, but also gets their eyes out of the bright light (unless they have nerves of steel, their eyes will naturally follow the gun), so the next time you raise the gun again, they're again partially blinded as their eyes try to adjust from looking at the dark table top.

It's all a slight of hand magic trick where the only thing special you need is the very slightly modified gun, which anyone could do with something as simple as a file.

watch a revolver in slow motion: the cylinder turns first, then fires. The top chamber of a revolver fires last. — Trish, Apr 27 '22 at 13:18
@Trish, that's irrelevant. I said "load the bullet into the chamber in relation to the index which is the one you want to use". I didn't say "notch the chamber with the bullet". All that matters is that you know what chamber the bullet goes into. It might be the third one clockwise from the index notch, it might be the one to the left. — Keith Morrison, Apr 27 '22 at 16:55

Englishman Bob · Answer 15 · 2022-04-26T02:11:30.850

Monte Carlo Simulation

A variation on @tristan's

Don't rig it, predict it.

Keep all variables the same: bullet, position, force of spin, temperature in the room, humidity... Rerun the exercise as many times as possible (read in the millions) checking the position of the round. Plot the position of the round using a pie chart.

Just be sure the amount of lubricant and replacement parts are from the same manufacturer and of sufficient quality before placing it against the head. But, then again with a sufficiently precise scale an equipment you could account for the variability here too.

https://en.m.wikipedia.org/wiki/Monte_Carlo_method