Dummy that will cycle the slide


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baryon
September 22, 2008, 11:32 AM
Hi,

I was wondering if it is possible to create a dummy cartridge by removing the bullet? Would it cycle the slide? In a SD situation may be it can be used to fire a warning shot and also cycle the slide. Is this feasible?

thanks

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LtShortcut
September 22, 2008, 11:35 AM
No. Don't do it. Buy a blank firing pistol and some blanks to go in it.

Again, don't fool around with what you are thinking.

Justin
September 22, 2008, 11:37 AM
Blanks will not cycle a weapon unless they have been modified with a blank adapter. If you just pull the bullet out of the case, it won't work as the powder will simply spill everywhere. Blanks are actually crimped shut to keep this from happening.

If you aren't willing to use lethal force to defend yourself, you need to look into an alternative method such as pepper spray or a taser.

baryon
September 22, 2008, 11:46 AM
Of course it needs to be filled in with something light weight(wax?) so that the powder doesn't spills out.

My question is basically whether this is technically feasible not from legal or tactical angles.

rcmodel
September 22, 2008, 11:52 AM
NO. Not technically feasible.
As already noted, the only way a blank can develop enough pressure to cycle an action is by reducing the hole in the bore with a "Blank Adapter".

Without the recoil & pressure of an actual energy developing load, the action will not cycle.


Further it is bad from both a tactical & legal standpoint to be popping blanks at another human.

Blanks or not, if you fire a gun at someone, it is considered firing a gun at someone by the law.

And a lot of experienced gang-bangers would just respond by shooting you several times with real bullets!

rcmodel

Aran
September 22, 2008, 12:03 PM
Forget the experienced gang-bangers, I imagine anyone armed would probably at least consider return fire.

kingpin008
September 22, 2008, 01:00 PM
Other have covered the technical aspect, so let me repeat the legal/tactical bit:

IF YOU NEED A WARNING SHOT, YOU SHOULD NOT BE SHOOTING AT SOMEONE/SOMETHING TO BEGIN WITH.

Sorry for the caps-lock, but it's that important. Warning shots are a bad thing. If you're in enough danger to have to use a gun, you'd better use it to put the threat down - and that means you -shoot the threat- not -warn it away-. The time for warnings should have come before you were forced to pull the gun. Period.

General Geoff
September 22, 2008, 01:03 PM
Also note that blanks can be very harmful if not fatal to the person the gun is being aimed at out to at least a few feet.

SDC
September 22, 2008, 01:08 PM
The only reasonably close thing to something like this that I've seen has been in conjunction with one of the "laser"type training simulators; these used cartridges of the same dimensions as a loaded round, but were pressurized with compressed air that was released when the firing-pin hit the "primer"; the air also caused a laser unit that plugged the forward half of a drop-in barrel to fire a laser pulse at the screen showing a scenario. The recoil impulse caused by the air was just enough to cycle the gun (I saw SIGs, Berettas, and MP-5s modified to work this way), and the ejected cartridges could easily be re-pressurized to be re-used. From a non-training standpoint, it's a bad idea; if someone is doing something worth shooting them, shoot them.

bdickens
September 22, 2008, 01:15 PM
Aaaaaaggggghhhh!!!!!!! :eek:

Boris
September 22, 2008, 02:52 PM
If you truly need a warning shot for whatever reason, then just miss on purpose. Normally just pulling the gun is enough of a warning. If they don't run from that then they won't run period.
If however it is necessary for you to put someone down in a hurry, having to shoot away that warning shot to get to the real ammo will just waste time and can end badly.

wyocarp
September 22, 2008, 07:10 PM
If you truly need a warning shot for whatever reason, then just miss on purpose. Normally just pulling the gun is enough of a warning. If they don't run from that then they won't run period.


I have done this. I had a guy coming at me with his hand behind his back. It was dark and I told him to stop. I forcefully repeated my request for him to stop numerous times. Me pulling my gun didn't stop him. When I fired a round and trained my gun on him again and demanded that he stop, he did. The next round would have been not have been a warning and I guess he believed me when I told him so.

kingpin008
September 22, 2008, 07:48 PM
That's great that it worked for you - still doesn't mean it's a good idea. If nothing else, it leaves you with one (or more, if you decide to take more than one warning shot) less round to use to preserve your life.

I don't know about you, but I'm not too proud to admit that in a situation where I may have to pull and use a gun, I won't be in possession of my zen-like target-blasting ability I have on the range. Rounds will likely miss, or they will probably need follow-ups to be effective. Warning shots waste that ability, with negligible benefit.

And if I may ask - where were you when this situation occurred? Where did your warning shot go, if not into the badguy? That's yet one more reason warning shots aren't a good idea - when shooting a badguy, you have a definite target and backstop - his/her body. While you may miss in the process and strike another target, at least you were firing in immediate defense of your life. With a warning shot, you have committed yourself to taking the time to deliberately miss that target which essentially robs you of that verified target/backstop.

And before you say "oh, I shot into the air or down at the ground." - neither of those are safe or acceptable backstops. Bullets shot into the air keep going, and can potentially strike a target downrange, just like a bullet shot at the ground which ricochet's can.

Warning shots = bad idea.

Boris
September 22, 2008, 07:57 PM
Also people continuing to bother you even when faced with a gun is more the exception than the norm, unless they have a gun themselves. In which case, start shooting.

wyocarp
September 22, 2008, 08:04 PM
kingpin, I couldn't disagree more.

Rounds will likely miss, or they will probably need follow-ups to be effective.

I don't practice to miss. Since my hobby is calling animals, bears are my favorite, I've had a lot of instances where I get to practice quick split second shots that need to be on target.

I could have shot the guy and I think that my life would have had more problems than the problem of only having 5 rounds left in my revolver. If I can't stop someone with rounds of .357 mag, then I'll just have to resort to scrapping it out with a bloody guy.

Tacbandit
September 22, 2008, 08:12 PM
"I was wondering if it is possible to create a dummy cartridge by removing the bullet? Would it cycle the slide? In a SD situation may be it can be used to fire a warning shot and also cycle the slide. Is this feasible?"



Don't go there...do the right thing, get yourself set up right

KelVarnson
September 22, 2008, 08:24 PM
I don't see how someone, regardless of experience, can say that a warning shot is always a bad idea. That's quite a generalization.

.cheese.
September 22, 2008, 08:32 PM
Technically, it IS possible to create a dummy cartridge - but what you're really making is a blank. No, it will not cycle the slide though. Blanks typically are made by using a casing that is longer than a typically sized casing and crimped in such a way that the crimp actually forms the basic shape of a bullet. This makes it possible for them to feed in semi-automatic fashion. To get the gun to cycle though, blank-firing guns require a modification to constrict the gas flow so as to provide enough force to cycle the slide. Additionally, often the recoil spring will be replaced with a lighter one that will move with less force required.

This is essentially what you see with prop guns used in movies and on tv. Once a gun is modified to use a blank, it CANNOT use regular ammunition without being converted back to its original configuration.

Some guns, like ARs and AKs can function with blank ammunition with a simple device that attaches to the end of the barrel. Most other guns though require more significant modifications and entire businesses exist just making blank firing weapons, maintaining them, and manufacturing blanks for them.

Under NO condition is a blank to be used in self-defense.

1) To do so, you'd have to use a gun that could ONLY fire blanks. Or, manually cycle the slide after firing the blank.

2) Legally, you shouldn't be firing a weapon unless you intend for a projectile to hit your target. Warning shots are an often discussed topic and the consensus is that they are a horrible idea all around. (trust me, it's been hashed out a zillion times on every gun forum online),

3) Even a blank can kill a person. There is no telling if the metallic cartridge will rupture causing a piece of metal to go flying at bullet-like speed. This is why in movies and tv, the actors rarely actually point the guns at each other, the magic of film/tv just makes it look like they do. If you think a film executive is going to let a potentially lethal weapon be pointed at a star, think again. They have already learned their lesson. Look up "Brandon Lee" on Google for more info. Mistakes are made, and blanks are not guaranteed not to cause injury.

4) This is easily done with revolvers, but see the above reasons for why you should still not do it.

5) If pointing a gun at somebody to fire a blank, don't expect them to know it's a blank! To them, you've just presented a credible threat of death and/or severe bodily harm and they have just gained the right to point a gun at you with REAL ammunition and pull the trigger.

If after all this, you are still comprehending the idea, I don't know what to tell you.... it's a bad idea. It's good to see you're thinking about possibilities, and don't let this put you off from coming up with other ideas, but as you can see, bouncing ideas off the community can often show you a side of something you hadn't thought of and can potentially save your butt. In this case, it's well established that using blanks in self-defense is a bad idea and a good way to either end up in jail or more likely - dead.

Here at THR, we'd rather you avoid both. :)

Most of us here deal with having less-lethal force available in addition to lethal force. Pepper-spray, stun-guns, etc. are all good ways to defend yourself when force is warranted, but not deadly force.

If you tell us what state you're in, somebody might be able to recommend a book that will help you familiarize yourself with the relevant laws. This is EXTREMELY helpful.

SCKimberFan
September 22, 2008, 08:33 PM
If you aren't willing to use lethal force to defend yourself, you need to look into an alternative method such as pepper spray or a taser.

This cannot be overstated.

If you truly need a warning shot for whatever reason, then just miss on purpose.

BAD IDEA. One of the 4 rules. Know what is around, behind what you are aiming at. Who knows where that bullet will end up?

kingpin008
September 22, 2008, 08:57 PM
I don't practice to miss.

Does anyone? I've never understood that particular reasoning as justification for warning shots/only carrying so many rounds of ammo. Nobody in their right mind practices to miss - why are you any different?

I've had a lot of instances where I get to practice quick split second shots that need to be on target.

Ok, but the problem with that, is that you go into the activity expecting to confront and interact with an animal. You've prepared yourself to take that split second shot, if only in the sense that you've said "ok, I'm going calling today. Gonna have to be ready to rock 'n roll if things go sideways." That's a heck of a lot different from running day-to-day errands, where you sometimes slip in and out of situational awareness, and you have a much harder time controlling the environment.

If I can't stop someone with rounds of .357 mag, then I'll just have to resort to scrapping it out with a bloody guy.

Spoken like a guy who's never had to scrap it out with a fellow who's just been shot five times at conversational distances. You also must account for the fact that while you were shooting, the target was also likely advancing on your position - forcing you to either move and shoot, or stand static and take whatever blows they were able to dish out. Maybe it's just me, but that seems like a great time to have one more round to work with.

As always, just my two cents. I respect your opinion, and your right to have it - even if I don't agree with it. I just worry that should the time ever come to put those beliefs and opinions into action, most won't have the same luck you've apparently had so far.

baryon
September 22, 2008, 09:08 PM
Thanks for all the replies. The reason for asking this question is statistics show that many volatile situations end by merely pulling a gun. And many more end after firing a single shot. Shooting someone changes your life forever. That is why I want to avoid doing it. Of course, if there is no other way then one has to make that decision.

By the way, nobody answered what happens if I do create a dummy by removing the bullet and put some filler in there. If I fire that cartridge what happens to the slide? Does it stay as it? For every action there must be some reaction. Don't rockets, missiles propel forward by the expulsion of the propellant? The slide is analogous to the missile and the burnt gun powder is the propellant. Am I right?

KelVarnson
September 22, 2008, 09:19 PM
By the way, nobody answered what happens if I do create a dummy by removing the bullet and put some filler in there. If I fire that cartridge what happens to the slide? Does it stay as it? For every action there must be some reaction. Don't rockets, missiles propel forward by the expulsion of the propellant? The slide is analogous to the missile and the burnt gun powder is the propellant. Am I right?

I think what is missing from your equation is the inertia from the mass of the bullet. Without that inertial load to work against, the gasses escape much more quickly and with much less resistance, and so therefore generate much less rearward force on the slide.

kingpin008
September 22, 2008, 09:25 PM
Baryon - part of why nobody has really answered your question, is because it depends on a lot of factors. Such as: how powerful is the particular primer in the shell you've emptied and replaced with filler? Is it powerful enough to burn through whatever you've used as filler, and propel the bullet from the case? If so, was the force also sufficient to cycle the slide? If so, to what degree? Was it able to fully cycle the slide, or just partially?

And such and so forth. I can tell you that one thing you're extremely likely to do with such a setup is create a squib, which is a bad thing. Basically, a squib is when a round is fired but is not powerful enough to propel the bullet completely out of the barrel, thus creating a blockage. Now, sometimes this occurs and the shooter notices it and can deal with it accordingly, and sometimes it occurs and the shooter continues firing, potentially blowing up their gun and injuring themselves. Injuries from such an event can seriously damage or even kill you, depending on what type of round is being fired and what type of gun is being used. They're nothing to mess with.

Unless a gun is specifically designed or otherwise equipped to run with blanks or down-loaded cartridges, it's not a good idea. Please don't do it, especially in a firearm that is being depended on to save your life or the life of a loved one.

protolith
September 22, 2008, 10:15 PM
By the way, nobody answered what happens if I do create a dummy by removing the bullet and put some filler in there. If I fire that cartridge what happens to the slide? Does it stay as it? For every action there must be some reaction. Don't rockets, missiles propel forward by the expulsion of the propellant? The slide is analogous to the missile and the burnt gun powder is the propellant. Am I right?
I think what is missing from your equation is the inertia from the mass of the bullet. Without that inertial load to work against, the gasses escape much more quickly and with much less resistance, and so therefore generate much less rearward force on the slide.

I think this should be theoretically possible with blowback style actions (it might not have even been done successfully).
If the cartridge has a properly designed nozzle to achieve correct chamber pressure, you should be able to simulate the pressure response to a normally fired round. This is clearly going to be more complicated than a simple crimped case or wax plug - and probably far from cost effective (see Gyroget)

As for gas operated designs like an AR, AK, SKS, or FAL, the only way to cycle a blank will be with a blank adapter as the action cycles on pressure in the barrel and not at the chamber (the blank adapter will have to be removed prior to firing any real bullets, or else you will have kaboom in your face).

As for the tactical ideas for the blank, the responses suggesting you avoid are because 99 out of 100 SD threats will be ended by the sight of a gun, 99 out of 100 times that shots are fired, one will do (whether it hits or misses it should have been a real shot - any caliber will also usually do in this scenario)

in the 1 in 10,000 times multiple follow up shots are required, you will need every shot you have, and probably more than that. This is the area of caliber debates (9mm vs .45ACP) this is the area of back up guns, NY reloads, extra mags, hi cap mags and the like, this is the area of stopping power vs high round count. This is the area that Everyone that carries shouldn't want to be in but does want to survive.

If you trust the statistics, join the heard, you don't need a gun. I would rather be prepared for the 1 in 1:1,000,000 scenario but never need a weapon, than find myself in that scenario regretting a single wasted/ineffective shot.

blackhawk2000
September 22, 2008, 10:16 PM
Very bad idea.

If you are not prepared to take a life you shouldn't be carrying in the first place.

wagoneer1019
September 22, 2008, 10:37 PM
I have heard from some former LEO's in the pre-taser days of the 1970 and 1980's they yould have snake shot the first round up in there revolvers as a less leathel option and the shot-gun affect of not missing. what do you think? out in the desert I will have snake shot for rattle snakes, and took a rabbit with it once but it took 2 rounds to do the job, so it will draw blood but its kinda weak

kingpin008
September 22, 2008, 10:58 PM
I dunno about you, but if I have to shoot someone to stop them from being a threat to my or my family's life, I don't care about wounding them. I care about incapactitating them. That means making it physically impossible for them to keep moving - snake shot will not do that.

Look - if you shoot at a badguy with some sort of less-than-lethal round (rubber bullets, snakeshot, rock salt, whatever) and you wound the hell out of him and he stops, fine. Awesome. But be prepared to sit in court and justify to his lawyer and a jury how you felt the need to pull a gun on this poor, disadvantaged, misguided inner-city youth yet you weren't in sufficient fear of your life so you used non-lethal ammo.

I can almost guarantee you they'll tear you apart.

akodo
September 22, 2008, 11:12 PM
If you aren't in such immediate danger that you need a REAL gun with REAL ammunition, then aren't in enough danger to use a bluff gun and fake bullets

KelVarnson
September 22, 2008, 11:12 PM
I think this should be theoretically possible with blowback style actions (it might not have even been done successfully).
If the cartridge has a properly designed nozzle to achieve correct chamber pressure, you should be able to simulate the pressure response to a normally fired round. This is clearly going to be more complicated than a simple crimped case or wax plug - and probably far from cost effective (see Gyroget)

As for gas operated designs like an AR, AK, SKS, or FAL, the only way to cycle a blank will be with a blank adapter as the action cycles on pressure in the barrel and not at the chamber (the blank adapter will have to be removed prior to firing any real bullets, or else you will have kaboom in your face).

Very interesting comments! I was thinking in terms of recoil-operation, not blowback or gas. You may have surmised that. Thanks for making me think about it some more.

baryon
September 23, 2008, 12:02 AM
http://video.google.com/videoplay?docid=6153240995617731728&vt=lf&hl=en

If coke+mentos can propel a bottle, I think a 9mm or .40S&W cartridge should have enough power. don't you think? Now, who is going to try it at a gun range?

NeoSpud
September 23, 2008, 12:19 AM
Baryon, you're missing the point. Let me put it this way: if you dropped a mentos into a glass of diet coke, what'll happen? It'll fizz over, not moving the glass one bit. The bottle in your video moves because of the gas trying to escape the constricted "nozzle" where the cap screws on. That's how blank firing adapters work, generally speaking. Without the BFA, which would make shooting conventional ammo immediately afterwards impossible, it just won't work with 9mm and .40S&W.

AFAIK, the gas will simply follow the path of least resistance, right out the barrel, without imparting significant rearward force to move the slide and chamber a new round.

I could be way off here, of course, but it just doesn't seem feasible (or smart, tactically).

kcshooter
September 23, 2008, 12:27 AM
If coke+mentos can propel a bottle, I think a 9mm or .40S&W cartridge should have enough power. don't you think? Now, who is going to try it at a gun range?Not a physics major, eh? Every action has an equal and opposite reaction. The action created by the blank doesn't create a reaction strong enough to overpower a recoil spring. It just won't work, period, no need to try this one at the range.

If the cartridge has a properly designed nozzle to achieve correct chamber pressure, you should be able to simulate the pressure response to a normally fired round.
What chamber pressure? You can't pressurize an open tube.



Also, what the hell is a "warning shot"??

Frank Ettin
September 23, 2008, 01:09 AM
[1] Fpr every action there is an equal and opposite reaction. The energy of the "action" is a function of the mass shot down range. The reaction is equal to it and is necessary to make the gun cycle. The mass sent down range when firing a normal cartridge is the bullet plus the mass of he gas created by the burning of the propellant. The mass going down range when firing a blank is merely the mass of the gas. This is a substantial difference and makes a substantial difference in the energy of the "reaction." The former can cycle the gun. The latter can not.

[2] In order to make guns cycle with blanks for the movies, the special effects wizards modify the gun by constricting the bore and using a light recoil spring. These modifications are incompatible with firing live ammunition.

protolith
September 23, 2008, 01:47 AM
If the cartridge has a properly designed nozzle to achieve correct chamber pressure, you should be able to simulate the pressure response to a normally fired round.
What chamber pressure? You can't pressurize an open tube.

Think of how a blowback action works. As the powder is burning the expanding gas forces the bullet down the barrel and the chamber pressure initiates the cartridge pushing on the slide, the bullet exits the barrel and the combustion ends, the inertia initiated during combustion continues and carries slide back to the stop, the casing is ejected and the recoil spring returns the slide.

This all requires proper timing and a proper balance between chamber pressure, recoil spring tension, and balance with the slide, powder load, bullet weight, etc.

The reason simple blanks don't work is without a slug forming a partial seal in the barrel while being propelled down the barrel the normal chamber pressure is not achieved. A blowback design firing blanks only works with a much softer recoil spring.

From your statement, I assume you already know this part.

Now to make a blank that will cycle a regularly set up blowback action (standard recoil spring), we will need a specially designed casing with a much thicker casing wall and a nozzle in the end so the correct chamber pressure occurs within the casing. The thicker casing wall will attempt to contain the pressure long enough to at least initiate the action and the gun will cycle as designed.

I am not trying to suggest this would be trivial to develop. In fact I think it would be quite difficult to get the balance with the thickened casing wall, nozzle opening, temporary sealing technique (small wax plug, or some sort of crimp past the nozzle) and finding the right rate of powder burn to generate a proper recoil impulse. All without blowing itself up or shooting the primer out of the pocket.

The main reason this has never been properly developed (as far as I know) is likely due to the fact that there is really no good reason to mix banks and real rounds in the same gun, In fact I agree this is a tactically dangerous proposition. It makes better sense to require either modification of the gun (weaker recoil spring) or installation of a blank firing device to ensure that there is no confusion as to the state of the firearm, blanks for training, or real ammo for intended purpose - and never the two mixed. Thus its not worth the effort to engineer when a simpler method of firing blanks already exists.

So I again submit that it should be theoretically possible (in blowback designs) to engineer a blank round that will properly cycle.

If your statement:
What chamber pressure? You can't pressurize an open tube.
was regarding gas operated designs that bleed pressure from ports in the barrel like the M1Garand/M1carbine/M14/M1a/mini14 design or the AR (stoner) design or the AK/AKM (Kalashnikov) design or the FAL/G1/G3 design or any other gas operated design. I agree that no amount of special blank design will work without chamber restriction in the barrel somewhere past the gas port. Reread my post and you will see I stated this.

FSCJedi
September 23, 2008, 06:34 AM
Not trying to sound like a smart a$$ here, but you guys who are trying to figure out the mechanics of this blank cartridge that cycles the slide are just enabling the OP...

*shrug* Just my $0.02.

.cheese.
September 23, 2008, 06:39 AM
protolith - I'm not following you.

It sounds like what you're thinking of is making a cartridge that works like a little rocket pushing backwards on the slide. I'm not fully grasping what the thicker casing has to do with it though?

Also, somehow I just don't think you could do that in a safe way.

1) You'd need a lot of energy/powder

2) What happens during ejection? The cartridge would basically be a gyrojet projectile flying backwards at the shooter. So you'd shoot yourself or some guy to your side.

Might as well just go all the way with that concept:

http://www.theodoresworld.net/pics/0608/backwardgImage1.jpg

baryon
September 23, 2008, 08:45 AM
Not a physics major, eh? Every action has an equal and opposite reaction. The action created by the blank doesn't create a reaction strong enough to overpower a recoil spring. It just won't work, period, no need to try this one at the range.

Studied Engineering. May be I slept in Physics class:D My Coke bottle analogy is not bad. If the liquid propellant coming out at low velocity can propel a heavy bottle(heavier than a slide) up in the air, is it not feasible that the gun powder in a cartridge that is fully burnt in about 15ms generates enough pressure to move the slide by 3 inches? The slide hasn't got to slam back. Just enough velocity to eject the empty cartridge and clear the top of the magazine.

A quick search shows that thrust is dm/dt*v where dm/dt is the rate of change of the mass of the propellant coming out and v its velocity. The key is to find these values so that it can overcome the recoil spring + slide.

I think the front portion of the cartridge may have to be shaped so that it behaves like the nozzle of a rocket and acts like a micro rocket pushing the slide back.

baryon
September 23, 2008, 08:52 AM
and finding the right rate of powder burn to generate a proper recoil impulse.

You might have a point there.

kcshooter
September 23, 2008, 12:18 PM
You aren't getting it. You can't simulate chamber pressure within the cartridge. The pressure needs something to push against, an obstruction within the barrel. Be that obstruction a bullet or blank adaptor or some other type of plug, you need something for the force to push against to move the slide. It just simply won't work. It would require a dangerous amount of explosive force to get it to move even a slight amount. To equate it to a bottle analagy requires a much longer buring period and no force acting upon the slide to keep it in place, so while this may work to open the slide slightly with no recoil spring in place, it wouldn't close itself again, and would not have the force required to eject the casing. Once it moved back slightly, with no recoil spring mind you, enough to free the cartridge, you are again dealing with a completely open tube. Therefore, no pressure.

KelVarnson
September 23, 2008, 01:01 PM
Even open tubes have resistance to flow, if the pressure is high enough.

kcshooter
September 23, 2008, 01:03 PM
Even open tubes have resistance to flow, if the pressure is high enough.Yeah, now how much explosion would you have to have in your hand to get enough resistance to overpower the slide and recoil spring by creating enough pressure within an open tube.

Wow.
OK, if you think I don't know what I'm talking about, try it. Give it a shot. See what happens.

Joey_the_Wolf
September 23, 2008, 01:15 PM
Two hollowpoints to center mass should serve as a warning. If the perp still doesn't get the point, a well placed shot to the head, preferably severing the Medulla Oblongata, should resolve the situation. As many have stated here, warning shots will do you more harm than good in a self defense situation.

Frank Ettin
September 23, 2008, 01:21 PM
I'm backing kcshooter.

There are two ways to make a semi-auto work: gas pressure, like the piston in a car engine; and Newton's third law, "for every action there is an equal and opposite reaction."

Some guns do indeed work by gas pressure, the AR-15 for example. In those guns some of the propellant gas is bled off into a cylinder closed at one end by a piston that can move. As the pressure in the cylinder increases, it moves the piston, which moves an actuating rod to operate the action of the gun. Moving the piston requires forcing a large enough volume of gas into a small enough space. Pressure is a function of the volume of gas and the space confining it. A given volume of gas in a large, or rapidly expanding space, produces less pressure than the same volume of gas in a smaller, or slowly expanding space.

The other way is the opposite force created by firing the gun and shooting something forward. The opposite force is a function of the amount of mass going forward and the velocity of the mass going forward. Shooting a greater mass at a given velocity produces more rearward "recoil pulse" than a lesser mass at the same velocity. This is how a jet engine works. The engine expels to the rear a large mass of gas at very high velocity, and that produces a large enough opposite (forward) force to overcome the vehicle's inertia and move it forward. The exhaust doesn't push against anything.

But to make a recoil operated gun work, the amount of mass sent forward and its velocity must be sufficient to generate a large enough opposite force to overcome the forces holding the gun closed. In an auto-loading pistol, those forces to be overcome include the inertial mass of the slide, the recoil spring and, in a locked breach pistol like a 1911, the force exerted by the locking lugs.

Firing a regular cartridge, by far the largest component of the total mass going forward is the bullet. If the bullet were absent, such as in a blank cartridge, the mass of the gas going forward would have to make up for all, or most of the mass that would otherwise be provided by the bullet. That would be a huge volume of gas because the gas is far, far less dense than the material of which the bullet is made.

(BTW, a blow back pistol also operates from recoil pulse, not pressure. The defining characteristic of a blow back design is that the breach is not locked mechanically, and the action is held closed solely by the recoil spring. The pressure of the expanding propellant gas is not a factor. While the expanding gas does no doubt exert some pressure on the breach face, the size of the area into which the gas is expanding is rapidly increasing, effectively to infinite, as the bullet moves down and exits the bore. Therefore, the pressure falls off very quickly.)

Hollywood special effects wizards modify a pistol to cycle with blanks by constricting the bore to slow the drop off of pressure. They may also use very light recoil springs. A blank actuated gun thus works from pressure, but the modifications are certainly incompatible with live ammunition.

Of course, if someone thinks he can produce a blank cartridge that will create a large enough mass of gas moving forward at a high enough velocity to generate a sufficient recoil pulse to cycle a semi-automatic pistol, he's welcome to try. I'd be very curious to hear how it works out.

Even open tubes have resistance to flow, if the pressure is high enough.
Of course there are substances which, when ignited, will produce a large enough volume of gas quickly enough to produce appreciable pressure even when not confined. I think, however, that C-4 would be a poor choice for a propellant for a blank cartridge.

ny32182
September 23, 2008, 01:46 PM
Baryon, the only way the powder burns in milliseconds is if there is an obstruction in the bore (either a bullet or blank firing adapter) that will raise the pressure exponentially as the reaction begins. I guess a chemistry lesson you missed is that stuff burns much faster under high pressure. If you burn a pile of powder in the open air (essentially the same thing you are doing if burning it in a chamber with no bullet present), it will not burn quickly at all relative to the way it burns in a live round. It may take 1-3 seconds or more to burn depending on the powder. I know, because I've lit many small piles of powder in the open air. ;)

Your coke bottle analogy is more akin to having a blank firing adapter installed: The space for gas to escape is much smaller than the diameter of the bore/chamber; therefore a little pressure builds as the gas escapes. Enough to move the bottle. Enough to move the barrel, and thus the slide with a super-light recoil spring installed, in a blank firing gun.

If you are firing a blank with an open bore (no adapter installed), the analogy is what someone mentioned earlier: You are dropping a mentos into a rock glass with coke in the bottom: The opening for the gas to escape is the same diameter as the bore/chamber. No significant pressure builds. No kinetic energy is imparted to the barrel. None. And the recoil spring/lockup of a real pistol is a whole lot stronger than it is in a blank firing pistol.

KelVarnson
September 23, 2008, 02:16 PM
(BTW, a blow back pistol also operates from recoil pulse, not pressure.

Where do you think the "recoil pulse" comes from? It's from the expanding gas pushing between the bullet and the case. ALL of the energy that goes into moving the slide back comes from the expanding gas.

The pressure of the expanding propellant gas is not a factor. While the expanding gas does no doubt exert some pressure on the breach face, the size of the area into which the gas is expanding is rapidly increasing, effectively to infinite, as the bullet moves down and exits the bore. Therefore, the pressure falls off very quickly.)

I think you meant to say the "volume" into which the gas is expanding. Nonetheless, ALL of the energy imparted into the slide moving back and the bullet moving forward comes from expanding gas. True, as soon as the bullet leaves the barrel, the pressure drops drastically, but at that point the vast majority of the energy from the expanding gas has already beeen imparted into the slide and the bullet, and they keep moving in opposite directions.

In the OP's example, if there is no bullet mass/inertia to push against, the gas pressure will not get high enough to impart sufficient energy into the slide to cycle the action. I get that. In my previous statement, I was only saying, that pressure will not be zero just because the tube is not restricted. There will still be a pressure pulse, due to the inertia of the air/gas itself and the resistance to flow due to friction in the open tube.

Frank Ettin
September 23, 2008, 02:58 PM
Where do you think the "recoil pulse" comes from? It's from the expanding gas pushing between the bullet and the case....
It absolutely does NOT, at least if you're trying to say that the pressure of the expanding gas is what actuates the action of the pistol. A rocket engine with work in the vacuum of space where there is nothing for the exhaust gases to push against. It is simply that the force accelerating the gases to the rear also produces an equivalent forward acceleration.

The bullet is propelled forward by the expanding gases. But the recoil pulse is not produced by the pressure of the gas. As set out in Newton's Third Law, the force that accelerates the bullet forward produces an equal and opposite acceleration which is the rearward recoil pulse.

A relatively larger force is necessary to accelerate a relatively massive bullet, and a significantly less massive volume of gas, forward; and the force will be the same to the rear and accelerate the mechanism of the pistol to the rear. The force accelerating something far less massive, like simply a quantity of gas. will be considerably less.

While the pressure of the expanding gas is the motive power for the bullet, the recoil pulse is not produced by the pressure directly. It is an artifact of the forward acceleration of the bullet.

KelVarnson
September 23, 2008, 03:28 PM
The bullet is propelled forward by the expanding gases.

Agreed.

As set out in Newton's Third Law, the force that accelerates the bullet forward produces an equal and opposite acceleration which is the rearward recoil pulse.

Agreed. And with the combination of these two statements, you have just said that it is the expanding gas that propels the slide back. And you are correct.

The expanding gas from the burning gunpowder is the ONLY source of energy in the gun. All of the energy that it takes to move the slide back comes from this expanding gas.

But it is an equal and opposite reaction. The amount of energy imparted into the bullet (during the time its in the barrel) by the expanding gas should be equal to the amount of energy imparted into the slide. Of course, some of the energy put into the slide moves the rest of the gun, too, since the slide and the gun are connected. But, all of the energy moving the bullet forward and the slide backwards comes from expanding gas.

NG VI
September 23, 2008, 03:31 PM
In a SD situation may be it can be used to fire a warning shot

Terrible idea. If you need to warn someone off, do it by directing their eyes straight down the bore and instruct them that the flightplan of the next few moments depends entirely on their actions.

Sean Dempsey
September 23, 2008, 05:18 PM
Every single instructor for CCW has advised against warning shots.

It's a decent theory, but a horrible practice.

You fire a shot - everyone thinks its real. Now, instead of surrendering, the badguy feels he's being shot at and is going to die! So now he fights back with his own weapon and gun, assuming you meant to kill him.

It's like pretending you know karate to stop a fist fight.

jordan1948
September 23, 2008, 05:35 PM
My suggestion, if you don't want to use lethal force get a shotgun and some rubber buckshot or slugs.

rcmodel
September 23, 2008, 05:38 PM
A bad idea.

It's still considered shooting someone in the eyes of the law. And even rubber bullets are lethal at SD range.

rcmodel

Smithiac
September 23, 2008, 05:39 PM
A good portion of the kenetic energy needed to rack the slide comes from the pressure built behind the bullet exiting the barrel. What your thinking is not a good idea. If you are willing to pull your gun be willing to use it for the purpose of stopping someone with lethal force.

Smithiac

jephthai
September 23, 2008, 05:47 PM
It's a decent theory, but a horrible practice.

I wouldn't even give it that much credit. This question has been argued by experts here and on other fora a thousand times. Instead of this long, drawn-out discussion that somehow hints that the warning shout theory might have any merit at all, it should be a few links to previous definitive threads -- end of discussion.

Arguments against: (1) If you didn't need lethal force, you have a discharge of a firearm. I don't know about your city, but in mine that's illegal. (2) It wastes a round of ammunition. (3) You can't control ricochet, overpenetration, or its landing. (4) There is no legal clarity -- you may not even be firing your warning shot in "self-defense".

Arguments for: (1) I don't want to shoot somebody. (2) Maybe it will scare them "more".

I also think the blank thing is dumb. You invite all the legal trouble of the discharge of the weapon, hearing loss, possible injury if he's close, less useful ammo, etc. *And*, your semi-auto might not cycle to boot, in case you actually need the second one.

-Jephthai-

Sylvan-Forge
September 23, 2008, 05:57 PM
If you feel that you must fire a warning shot [IF FACED WITH A DEADLY THREAT] with your semi-automatic pistol:

Blanks or similiar ideas are not technically feasable to cycle the slide.

Use a manufactured blank and be prepared to cycle the slide by hand
OR
Select a cartridge that has a fragmenting bullet
AND only fire at an acute angle into the ground.
A shallow angle WILL ricochet.

.

Gottahaveone
September 23, 2008, 06:08 PM
If you're determined to fire a false first shot as some type of intimidation tactic, quit trying to repeal the laws of physics and just carry a revolver. Even racking the slide manually on an auto after firing the blank may well produce a jam at a time when you can least afford it. Course, you might be too busy dodging real lead to notice. :uhoh:

dmazur
September 23, 2008, 06:27 PM
Something to consider -

While the display of a gun has often permitted someone to escape, or forced a home invader to leave, there is no guarantee this outcome will occur.

Most training for self-defense (and I believe for LEO's as well) is to fire to neutralize the threat. Assess, engage remaining threats (if any) and continue firing until all threats are neutralized.

If you wait for the assailant to put his gun down, you may wind up dead. This can't be stressed enough. There may not be time for witty repartee, and the bad guy may not be following the same script you have in mind. It's not TV.

I've read that a concealed pistol should not be drawn as a threat, but as a last-ditch move to save your life. You should have already made the decision that your life is in danger before you draw.

(Investigating a noise at night is similar. The pistol is carried at "low ready", finger outside trigger guard. If there is a legitimate threat, it is brought to a firing position and used. Don't point until you are sure of your target.)

Do I have a universal answer for this? No. It is too complex a problem.

As others have said (or come close to saying), if you aren't ready to use deadly force appropriately to save your own life, you just may have the mental make-up of a victim. If so, forget about guns.

Frank Ettin
September 23, 2008, 09:03 PM
KelVarnson,

I've explained myself poorly. Let's try a different way to look at this.

Recoil energy can be calculated using the following formula:

WG = Weight of gun in pounds
WB = Weight of bullet in grains
WP = Weight of powder charge in grains
VB = Muzzle velocity of bullet in f/s
I = Interim number (Recoil Impulse in lb/sec)
VG = Recoil velocity of gun (f/s)
EG = Recoil energy of gun (ft lb)

I = [(WB * VB) + (WP * 4000)] / 225218

VG = 32.2 * (I / WG)

EG = (WG * VG * VG) / 64.4

This formula is quite similar to a formula for free recoil set out at http://en.wikipedia.org/wiki/Free_recoil, although I think that the formula from Wikipedia may be a little more precise based on what I've read in Hatcher's Notebook. The formula I've reproduced above, is from the Q&As at http://www.frfrogspad.com/miscella.htm (specifically the question about why some guns of the same caliber kick harder than others). John Schaefer (FrFrog) notes that, "..."4000" is the nominal velocity of the powder gases at the muzzle for commercial smokeless powder and the observed range is between 3700 and 4300 f/s. It is sometimes stated as 4700 in some sources but this is based on observations of artillery, not small arms...." The Wikipedia formula would use the actual powder gas velocity, which may not be readily available.

At any rate, the important point here is that recoil energy may be calculated based only on the weight (mass) of the bullet, the weight (mass) of the powder charge, the muzzle velocity of the bullet, the muzzle velocity of the powder gases, and the weight (mass) of the gun. Pressure is not a necessary parameter.

With this formula, your chosen auto-loader, a chronograph and various handloads for your gun, it should be possible to experimentally determine the minimum free recoil energy necessary to cycle your gun. So load up some ammunition using a range of powder charges going down quite light (this wold probably also work best with a light bullet for your chosen caliber). Grab your chronograph and head down to the range.

Shoot your gun with progressively lighter loads until you find the first one that won't cycle your gun. Thus the load just before that one, that still cycled the gun would be a fair approximation of the lightest load that would cycle. Chrono that load.

You now know the bullet weight, muzzle velocity, and powder charge for the lightest load that will cycle your gun. You also know the weight of the gun. You can now calculate the minimum recoil energy needed to cycle the gun.

Now it would be a simple matter to calculate the minimum powder charge and/or powder gas velocity that would be necessary to produce that minimum recoil energy with a bullet weight and bullet muzzle velocity of zero, as in a blank cartridge. You probably would want to use the more precise Wikipedia formula that uses actual powder gas velocity. And since you have an equation with two unknowns, there won't be a single answer.

So now all you have to do is load up some blank cartridges with the necessary amount of powder, and you'll be in business.

But wait a second. Just looking at the formula it's pretty obvious that with a bullet weight and bullet velocity of zero, you'll need an awful lot of powder to reach your minimum target recoil energy, at least with a nominal powder gas velocity of 4000 fps. Of course, to get the powder charge required down to a manageable level, you might need an extremely large (shall we say explosive) powder gas velocity.

I personally don't think it can be done. The foregoing are some tools that may help if you want to give it a try.

bogie
September 23, 2008, 09:08 PM
I'm just wondering where we got the original poster...

When I was half his age (just guessing at it...) I knew how guns work...

Must be kinda difficult if all you know about the subject comes from video games tho...

KelVarnson
September 23, 2008, 09:41 PM
Fiddletown,

Nice that you went to all of the trouble. However, I never said that a blank would cycle a semiauto gun, nor do I wish to try to make that happen. I merely pointed out that the pressure upon firing a blank would not be zero, just because the barrel was unobstructed. Therefore while it is not theoretically impossible that a blank could cycle a gun, as you pointed out it is practically impossible with typical rounds and typical guns.

Nonetheless, I would not want to hold my hand in front of the muzzle while firing a blank. I'm sure the pressure would be substantial.

Also, regardless of the fact that pressure is absent from your formula, it is still pressure that makes the gun work. Again, ALL of the energy that moves the slide and cycles the action comes from expanding gas. There is no other energy source. During the time the gas is pushing the bullet forward, it is pushing the slide back. When the bullet leaves the barrel and the pressure drops radically, there is no more energy to speak of being put into the slide, but it continues back due to momentum.

Using your experiment, with progressively-lighter loads, you will get corresponding drops in pressure, until the pressure is too low to fully cycle the action.

novaDAK
September 23, 2008, 10:07 PM
If you use a firearm (regardless of the type of ammo) the court is going to see it as lethal force.

As already stated, if you're not willing to take a life to save your own, don't carry a gun. Pulling a gun out and pointing it at the bad guy is enough warning. And if you draw a gun you better damn well be willing to go all the way and pull that trigger.

baryon
September 23, 2008, 11:03 PM
fiddletown, thanks a lot for your detailed post.

bogie, I know in detail how a 1911A, Glock and M&P works. I have read the patents(Glock, M&P) filed by the respective companies. I research a firearm in detail before I buy it. BTW I don't play video games and I am not from USA.

I never expected this thread to gather so many answers. My question was technical in nature and not from a tactical/legal aspect.

Richbaker
September 23, 2008, 11:13 PM
Most self defense handguns are recoil operated....no blank in the world will cause the slide to cycle, because it requires recoil.
If it does use some sort of gas -operated action, you will need a BFA to make it cycle, and cannot fire a real round without removing the BFA...

dmazur
September 23, 2008, 11:21 PM
baryon -

I read your qualification, but it's kind of difficult to remain silent in the questionable (but excluded) aspects of a question when you believe it can result in someone being harmed.

A somewhat strained comparison, but like asking how to conceal razor blades in candy, "technically, not from a legal angle." Very few people would be able to isolate the two aspects. Inveterate puzzle solvers, perhaps, but most would express concern that what you're asking about is dangerous and/or illegal.

I believe one of the posts used the term "enabling".

Sylvan-Forge
September 24, 2008, 09:33 AM
Aye, you put SD in there. Next time be more sneaky :)

We just don't want to hear that you got yourself hurt.

I can understand the warning shot part. Some loon, just plain rock dumb and/or wacked out on dope. A LOUD appeal could be neccessary to redirect them without having to live with the consequences or guilt of making them dead.

.

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