CO2 engineering question: Whats the optimum caliber and bore volume if you dump an entire CO2 cartridge?

I was thinking about how to put together an "air" powered muzzleloader, and my mind went right to the "hell no" safety issues of loading something with a "charge" of air already in the gun.  Second thought was to set it up to load a ball or if smoothbore shot, and then insert a CO2 capsule, and when fired, dump the whole cartridge.

Determining a practical caliber, barrel leangth and expansion volume is one of those science questions with numbers and stuff, so I was wondering if any of the wizards here could point me in the right direction. 

I'm assuming that I would need an expansion chamber and some sort of dump valve, and being that I'd like to keep the basic form of a full stocked long rifle, suggesting  a linear valve  arrangement design is the extra credit question....   Thanks, Woody

@bark_eater 

Woody;

Forgive me, but you are not making sense. And let me explain:

Pressure is pressure. A CO2 cartridge driven airgun is no safer than an HPA airgun if the pressure of the container is limited to about 950 PSI's. Why? the vapor pressure of CO2 at 25 °C/77  °F is 943 PSI, so, close enough.

For a single/dump valve shot, almost any normal for ML rifles external profile barrels with an increased ID can hold a decent charge of air at that pressure.

Using CO2 would be unwise because a full "dump" is so fast that it freezes the expansion chamber and the pressure drops, thereby becoming VERY inefficient.

Also, the KE of the bullet is proportional to the integral (area under the curve) of the pressure vs. the projectile travel in the bore.

A pressure dump is a right angle / scalene triangle that misuses half the bore length because it cannot maintain pressure along the bore travel of the projectile.

That is why SSP are relatively low powered airguns.

On the "positive side", your wish was already granted with the design of the Girandoni air rifle (one of which was used in the Lewis and Clark transcontinental expedition).

Just copy it. The designs and construction was documented in a book, which you can download here:

View on Scribd... by on Scribd

If you are only interested in this book, subscribe to the trial period and then cancel.

Otherwise, it is a very good resource to have.

If you DO decide to move forward, be prepared to revise a number of parts and dimensions because the writers clearly did not want to give away hard-earned secrets and they photographed and measured different parts from different rifles that may not always work well together.

Also be aware that the rifle does NOT have to be a repeating rifle, part of the complications in this design come from the magazine feed. A single shot can be much simpler, and the "timed valve" designed by Girandoni is truly ingenious and efficient at low pressures (about 900 PSI).

AND if you DO decide to move forward, I would strongly advise making half a dozen because you will be able to sell them at a very handsome price, LOL!

Believe me I will be rooting for you if you do decide to build them.

There are other ways to scratch this itch, but this one makes a good story and is interesting in the long run.

HTH, keep well and shoot straight!

HM

@hector_j_medina_g 

Hi Hector, The safety issue is the need to put your hands over the muzzle to load the gun, as well as pushing a rod/potential spear down the bore to seat the round or shot. I don't want to do any of that if there is any kind of pressure stored in the gun, so the manual of arms would be to load the projectile and then add a charge of pressure. 

It may well be a bad idea, but for a sense of scale, a 44 inch .75 caliber barrel has a volume of 19.44 cubic inches.

I could go for a larger caliber or longer barrel if it would match the expansion forces of a full CO2 cartridge.    I'm estimating that a 12 gram cartridge hold  enough CO2 to occupy 372.5 cubic inches at room temperature.   That's close to 20 times the volume of the barrel.  I have no real appreciation of what the the pressure dynamics would be.  I'm not sure this is a valuable comparison, but a 22 inch .22 caliber barrel has a volume of .84 cubic inches, which can be described as "the same" volume after 23 shots.    

Any chance I'm on to something? thanks, Woody

the thing is you could not dump a whole cartridge without moving the contents to another tank and even so you would waste 90% unless you made a canon like a pumpkin chucker 

now Cothran has been making very large TP valves they are about 125-140 bucks and with one of those a .25 caliber would be happy 

but you have amount of pressure and how it is used as the problem 

take a look at a Crosman 2240 the factory barrel 7+ inches wastes gas but a 10.1 inch barrel uses it better 

but then as stated you have the limit of the pressure in CO2 

you will start chasing your tail 

so the key will be valve size always because once the pellet or bullet is out the barrel all the gas in the world will not make it go faster 

Quackenbush Air Guns: Shot pistol

@marflow  I'm fine with starting with a pumpkin chucker and scaling back. My proposed baseline caliber and barrel leangth  looks to be 67 times the barrel volume of a 7.5 inch .22 caliber barrel.

@bark_eater,

Please realize that in the 18th & 19th centuries, there were a wide variety of muzzle-loading airguns intended for hunting, with a reservoir holding sufficient air for multiple shots in calibers up to .50.  A "poppet" type valve was usually used; the chance of catastrophic failure would be extremely small in such designs (as in current PCP's).  Normally a slow leak develops over time.

As noted above, trying to rapidly dump 12 grams of CO2 brings problems such as trying to vaporize the whole mass while it's cooling due to expansion, or even poking a big enough hole in the cartridge to achieve a fast dump.

Don R.

@oldair  Hi, I'll have to restate my safety concerns. It has nothing to do with catastrophic failure of a tank.  Its that I am unwilling to perform the action of loading a weapon from the muzzle with any kind of pressure in the gun.  I have some idea of how CO2 works, and it is my feeling things might work a bit differently when the barrel I am proposing has 67 times the volume of a Crosman 2240. The question is how to get the most out one shot with one CO2 cartridge, minimizing the inefficiencies of a potentially inefficient physics experiment.   It would probably be helpful to define "the most"  as Foot Pound Energy.

Found some info on a spud gun forum.  With my proposed barrel volume of 19.44 cubic inch the psi will drop to around 215 psi as the projectile  leaves the barrel.  If I assume 6 cubic inches for the volume of the cartridge and expansion chamber, I'm into 25.44 cubic inches or  around  165 psi.   Again I'm not sure how to interpret the numbers.  A .75 caliber ball weighs 499 grains / 1.14 oz. I'll do a bit more digging and find out what an optimum potato weighs...

https://www.spudfiles.com/viewtopic.php?t=26464

"
Made a chart long ago by unloading an entire 12g CO2 cartridge with the PSI results vs Chamber size in cubic inches.
This is at 72 degrees. Hotter and psi goes up, colder and the psi drops.

6 Cubic inches 700 psi 7 Cubic inches 600 psi 8 Cubic inches 525 psi 9 Cubic inches 466.666667 psi 10 Cubic inches 420 psi 11 Cubic inches 381.818182 psi 12 Cubic inches 350 psi 13 Cubic inches 323.076923 psi 14 Cubic inches 300 psi 15 Cubic inches 280 psi 16 Cubic inches 262.5 psi 17 Cubic inches 247.058824 psi 18 Cubic inches 233.333333 psi 19 Cubic inches 221.052632 psi 20 Cubic inches 210 psi 21 Cubic inches 200 psi 22 Cubic inches 190.909091 psi 23 Cubic inches 182.608696 psi 24 Cubic inches 175 psi 25 Cubic inches 168 psi 26 Cubic inches 161.538462 psi 27 Cubic inches 155.555556 psi 28 Cubic inches 150 psi 29 Cubic inches 144.827586 psi 30 Cubic inches 140 psi 31 Cubic inches 135.483871 psi 32 Cubic inches 131.25 psi 33 Cubic inches 127.272727 psi 34 Cubic inches 123.529412 psi 35 Cubic inches 120 psi 36 Cubic inches 116.666667 psi 37 Cubic inches 113.513514 psi 38 Cubic inches 110.526316 psi 39 Cubic inches 107.692308 psi 40 Cubic inches 105 psi 41 Cubic inches 102.439024 psi 42 Cubic inches 100 psi 43 Cubic inches 97.6744186 psi 44 Cubic inches 95.4545455 psi 45 Cubic inches 93.3333333 psi 46 Cubic inches 91.3043478 psi 47 Cubic inches 89.3617021 psi 48 Cubic inches 87.5 psi 49 Cubic inches 85.7142857 psi 50 Cubic inches 84 psi 51 Cubic inches 82.3529412 psi 52 Cubic inches 80.7692308 psi 53 Cubic inches 79.245283 psi 54 Cubic inches 77.7777778 psi 55 Cubic inches 76.3636364 psi 56 Cubic inches 75 psi 57 Cubic inches 73.6842105 psi 58 Cubic inches 72.4137931 psi 59 Cubic inches 71.1864407 psi 60 Cubic inches 70 psi 61 Cubic inches 68.852459 psi 62 Cubic inches 67.7419355 psi 63 Cubic inches 66.6666667 psi 64 Cubic inches 65.625 psi 65 Cubic inches 64.6153846 psi 66 Cubic inches 63.6363636 psi 67 Cubic inches 62.6865672 psi 68 Cubic inches 61.7647059 psi 69 Cubic inches 60.8695652 psi 70 Cubic inches 60 psi 71 Cubic inches 59.1549296 psi 72 Cubic inches 58.3333333 psi 73 Cubic inches 57.5342466 psi 74 Cubic inches 56.7567568 psi 75 Cubic inches 56 psi 76 Cubic inches 55.2631579 psi 77 Cubic inches 54.5454545 psi 78 Cubic inches 53.8461538 psi 79 Cubic inches 53.164557 psi 80 Cubic inches 52.5 psi 81 Cubic inches 51.8518519 psi 82 Cubic inches 51.2195122 psi 83 Cubic inches 50.6024096 psi 84 Cubic inches 50 psi 85 Cubic inches 49.4117647 psi 86 Cubic inches 48.8372093 psi 87 Cubic inches 48.2758621 psi 88 Cubic inches 47.7272727 psi 89 Cubic inches 47.1910112 psi 90 Cubic inches 46.6666667 psi 91 Cubic inches 46.1538462 psi 92 Cubic inches 45.6521739 psi 93 Cubic inches 45.1612903 psi 94 Cubic inches 44.6808511 psi 95 Cubic inches 44.2105263 psi 96 Cubic inches 43.75 psi 97 Cubic inches 43.2989691 psi 98 Cubic inches 42.8571429 psi 99 Cubic inches 42.4242424 psi 100 Cubic inches 42 psi 101 Cubic inches 41.5841584 psi 102 Cubic inches 41.1764706 psi 103 Cubic inches 40.776699 psi 104 Cubic inches 40.3846154 psi 105 Cubic inches 40 psi 106 Cubic inches 39.6226415 psi 107 Cubic inches 39.2523364 psi 108 Cubic inches 38.8888889 psi 109 Cubic inches 38.5321101 psi 110 Cubic inches 38.1818182 psi 111 Cubic inches 37.8378378 psi 112 Cubic inches 37.5 psi 113 Cubic inches 37.1681416 psi 114 Cubic inches 36.8421053 psi 115 Cubic inches 36.5217391 psi 116 Cubic inches 36.2068966 psi 117 Cubic inches 35.8974359 psi 118 Cubic inches 35.5932203 psi 119 Cubic inches 35.2941176 psi 120 Cubic inches 35 psi 121 Cubic inches 34.7107438 psi 122 Cubic inches 34.4262295 psi 123 Cubic inches 34.1463415 psi 124 Cubic inches 33.8709677 psi 125 Cubic inches 33.6 psi 126 Cubic inches 33.3333333 psi 127 Cubic inches 33.0708661 psi 128 Cubic inches 32.8125 psi 129 Cubic inches 32.5581395 psi 130 Cubic inches 32.3076923 psi 131 Cubic inches 32.0610687 psi 132 Cubic inches 31.8181818 psi 133 Cubic inches 31.5789474 psi 134 Cubic inches 31.3432836 psi 135 Cubic inches 31.1111111 psi 136 Cubic inches 30.8823529 psi 137 Cubic inches 30.6569343 psi 138 Cubic inches 30.4347826 psi 139 Cubic inches 30.2158273 psi 140 Cubic inches 30 psi 141 Cubic inches 29.787234 psi 142 Cubic inches 29.5774648 psi 143 Cubic inches 29.3706294 psi 144 Cubic inches 29.1666667 psi 145 Cubic inches 28.9655172 psi 146 Cubic inches 28.7671233 psi 147 Cubic inches 28.5714286 psi 148 Cubic inches 28.3783784 psi 149 Cubic inches 28.1879195 psi 150 Cubic inches 28 psi"

@bark_eater,

Maybe my mention of catastrophic failure wasn't well stated - I was referring to failure of the exhaust valve (not the reservoir) being a very remote possibility, as this is the only way air can get to the barrel and endanger the loading person.

Don R.

Posted by: @bark_eater

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@hector_j_medina_g 

Hi Hector, The safety issue is the need to put your hands over the muzzle to load the gun, as well as pushing a rod/potential spear down the bore to seat the round or shot. I don't want to do any of that if there is any kind of pressure stored in the gun, so the manual of arms would be to load the projectile and then add a charge of pressure. 

It may well be a bad idea, but for a sense of scale, a 44 inch .75 caliber barrel has a volume of 19.44 cubic inches.

I could go for a larger caliber or longer barrel if it would match the expansion forces of a full CO2 cartridge.    I'm estimating that a 12 gram cartridge hold  enough CO2 to occupy 372.5 cubic inches at room temperature.   That's close to 20 times the volume of the barrel.  I have no real appreciation of what the the pressure dynamics would be.  I'm not sure this is a valuable comparison, but a 22 inch .22 caliber barrel has a volume of .84 cubic inches, which can be described as "the same" volume after 23 shots.    

Any chance I'm on to something? thanks, Woody

Clearly you have not downloaded the book and have not even looked at diagrams of this masterpiece.

The Girandoni was NOT a muzzle loader.

It loaded either by the side with a spring loaded "moving chamber" or by unscrewing the barrel, putting a ball in the chamber, screwing the barrel back and shooting the ball out.

And, forgive me, but you are still not making sense.
At 950 PSI's ORings are perfectly capable of effecting an almost perfect seal. There is no need to make it a muzzle loader. A moving bolt with two O'Rings will be enough to make a breech loading device completely safe and operational.

I have a double barrel 50 cal Express ML, and I take suitable precautions because once you have loaded one barrel, the only thing preventing you from loosing a hand is your presence of mind to not put a cap in the first barrel. Even mid-cock notches have been known to fail.
In the same way, as long as the hammer is not pulled back and there is no tension in the hammer spring, the hypothetical rifle CANNOT release air into the barrel.

In the end, ANY airgun is just an amplifier.
You take some energy from a storage, and then, given a specific input, the stored energy "amplifies" the output.
If there is no input, there cannot be an output.

And there are many ways to prevent the system from having any input.

Having said that, and in the spirit of being pro-active, MANY years ago, I once put together a CO2 gun for a friend in South America, where they did not have a caliber limit, but (without a license) they couldn't use HPA, they had to use CO2.
The rifle was based on a Talon, with a 3/16" close on flow speed valve, ¼" opening gap with a full hammer strike.
An additional 35 cc's (about 3 times the 12g "Powerlet" volume) expansion chamber was added between the tank and the valve, there was a choking point between the two chambers at the top of the passage between them. Unless you were shooting downwards, or held the gun scope-side down, there was no chance to put liquid CO2 into the expansion chamber.
The Barrel chosen was a 0.43" Spanish from old surplus.
Barrel was 32" once re-shanked and the cartridge chamber eliminated, leaving only enough space for a 400 gr. / 0.44" cal. cast bullet.
After tests, it was concluded that the max MV achievable was about 650 to 750 fps (in tropical weather), with only 15 good shots for a full tank (500 CC's). The rifle also required about 5 minutes to come back to normal temperature.

BUT, the tests also showed that the bullet, cast of Lyman #2 alloy would go clean through an empty cast iron 6 cyl. monoblock. Hollowpoints were cast of "pure" lead.

Yes it was effective, no it was not efficient. At the cost of CO2 out there, he could have purchased surplus 7.62 mm rounds. Alas, dictatorships are seldom respectful of an individual's right to keep and bear arms.

Did it solve my friends problems? yes, the capybaras that were ravaging his patch disappeared, having learned that the property was protected and there were easier places to raid.

Under current technology, you can replicate this with HPA in a much more efficient manner, and unless you cock the Talon/Condor's hammer, there is absolutely no way that the gun can shoot the bullet or the ramrod out (with your hand along for the ride). BUT, there is no NEED to make the contraption a muzzle loader.

I really, really, really, advise you to read up on the achievements of the Airgunsmiths of old.

There are many lessons there upon which you can build. No need to repeat history.

HTH, keep well and shoot straight!

HM

@hector_j_medina_g  Hi Hector, while I share your appreciation for the Girandoni, and actually made a pilgrimage to see  an example at the  Lewis and Clark exhibit when it was in Philadelphia.

However, my design criteria requires muzzle loading and that the gun be a large caliber single shot and have no pressurized gasses contained until after the  gun is loaded via the muzzle.  I am clear on the fact that using 12 grams of co2  per shot is expensive and inefficient.  What I am looking for is information to help minimize  the inefficiency's.

Your capybaras gun is very interesting, and sounds like a much closer comparison.     Thanks, Woody

IIRC, DAQ made a .30 something caliber CO2 rifle. That may be a source to start to answer this question.

@bigbore I have a couple of his bandit pistols from 20 years ago and he was my first thought for who to talk into building such a thing. I'm just trying to do some research  before pitching the project to him.

One problem that I see with trying to use a CO2 cartridge dump is that there is no way for you to open the cartridge fast enough, and wide enough, to dump everything fast. You can demonstrate this by putting a CO2 in a vise, and use a hammer and largish nail to puncture the cartridge (wear gloves!). When you do this, you won't get the "bang" that you would need, you'll just get a jet of CO2 that will dump the cartridge over a couple of seconds.

A few years ago, I built a "big bore" 9mm gun that charges a plenum with CO2 or HPA, and dumps it very quickly through a QEV type valve that I made to handle the 800-1000 psi. With HPA (850 psi), it will push a 82 gr. pellet at about 600 fps, for about 65 FPE. CO2 gives a little less because CO2 is a denser gas. The plenum is only about 20 cc, as any larger plenum just dumps excess gas out the barrel after the pellet leaves (I experimented with this.).

@doug_wall  Its going to need some sort of expansion chamber.    I'm not sure  how much volume would be needed for the entire 12 gram cartridge to convert from liquid to vapor, but I assume that that would simplified the math for determining barrel  volume.  How long was the barrel on your 9mm?

My 9mm  barrel is 27 inches. If you have an expansion chamber, you'll never get decent pressure in the system, and you'll need to have a valve between the chamber and the barrel. As I said, the 12 gCO2 will never dump rapidly,, and an expansion chamber, without a dump valve, will only act as a buffer, and slow the pressure rise down even more.

12g liquid CO2 will vaporize into 105CC at 850psi. Trying to vent 105CC of gas through any system quickly will require a relatively large opening. Dumping the CO2 from the 12g will be holdup on the system. Blasting a certain amount of liquid CO2 directly into the barrel will allow the barrel to act as an expansion chamber. That's the way that most CO2 guns work.

@doug_wall Thanks for the numbers. I'll play with them shortly, though again I don't realy have much math/knowledge to do more than a 6th grade algebra...

I found an illustration of a dump valve on one of the  Spud gun forums. I lost track of the original link but here's the sketch.  Its been a while since I focused on such things but it looks like the triggering poppet could be rotated 90 degrees and be activated by a side hammer. Using a flintlock action would be fun, particularly if you could prime the pan.

@bark_eater That's a QEV valve that's the same function as the one that I made. It would be a lot cheaper to run as a bulk filled gun, which is basically what I made.

@doug_wall  I'm pretty adamant about having zero charge in the gun while muzzle loading.   It appears that there are refillable CO@ cartridges available in 12 and 8 grams.   Top of the pile searching has them costing about $20 a pop, but I dont think I'd need to many as rate of fire would be limited by the cooling effect.

@bark_eater If you are bulk filling, you can have a valve between the tank and the gun. You load the muzzle, open the valve to charge the plenum in the gun, shoot the gun. No need to have it charged while loading.

@doug_wall I'm getting there...  Back in the the day I was a projectionist running an arc light projector.  Reaching in there to change the rods was still stressful no mater how many times I checked the switches.  If I had been wrong I probably wouldn't have noticed...anything... ever...again...

ARS made a cane that shot a CO2 cartridge out the muzzle about 100yards.

Posted by: @doug_wall

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@bark_eater If you are bulk filling, you can have a valve between the tank and the gun. You load the muzzle, open the valve to charge the plenum in the gun, shoot the gun. No need to have it charged while loading.

That's the answer.  If you must muzzle-load, as opposed to a rolling block or even a break barrel, then just add a valve in between.  

@ Bark_Eater

This just occured to me, LOL!

It may seem an outlandish idea, but I think it would be real fun:

Build a 10 gauge rocket launcher.

😉

So, the details:

First, get a custom fowler barrel made:

https://ricebarrels.com/product/46-new-england-fowler/

Then you will need to build an "action" into the solid rear plug that carries a piercing needle and a check valve.

The idea would be that you add fins and a head to the CO2 cartridge, which would then be loaded Mouth-Downwards into the barrel, and a wad placed over it, that would be your "load".

When the hammer strikes, the CO2 cartridge gets pierced and the CO2 gas coming out of the mouth becomes a rocket engine.

In this case, the CO2 cartridge itself is the projectile and the task at hand needs to be done by the added head.

Because the 10 Ga barrel is 0.775" you have about 0.045" to play with in total, the "wall thickness" of the carrier or sabot, would have to be half that. There is UHDPE tape for furniture runners that is about 0.030", so that could be an expedient way to add a "bearing" to the CO2 cartridge. The fins would need to be moulded out of plastic, but they do not have to be like "feathers", a simple air-foil of a profile would impart the spin.

The barrel proposed is already long, but the exiting CO2 would keep adding speed to the projectile even after leaving the bore.
Successive shots will not be too affected because what cools substantially down is going out of the bore each shot.

You MAY try to get a custom rifled barrel made in 10 Ga (more expensive and not without some legal ramifications), and then you COULD add a lead projectile in front of the "propellant/load train" with wads for retention and separation, but I would rather make the rocket launcher, LOL!

Just an idea.

Keep well and shoot straight!

HM

@hector_j_medina_g 

I once built a CO2 mortar that fired 12g cartridges. 36" of 3/4" copper piping with a piercing pin at its base. It worked really well, but the lack of rifling or stabilizing fins made for unpredictable accuracy. It was entertaining, but expensive to operate.

@jim_in_pgh 

Well, the premise of this whole exercise was to :"dump an entire CO2 cartridge?"  , so...

Just keeping with the OP's intent.

😉

Keep well and shoot straight!

HM

@bark_eater  In .30 cal. you can get multiple shots @ 50 foot pounds from a 12 gram cart. It's possible to go to larger calibers,  but the velocity will go down  as you go up in caliber. A fellow made a co2 gun that fired a 1000 gram projectile @ 300fps. out of about a 6 foot barrel.