Volume of gas generated by 22LR round

If I had a lick of hair left, I would have already done these experiments. But maybe some other curious soul has already done something like this, or maybe the literature covers it but I have not found it yet:

Take a 2 liter pop bottle, and fill it ½ full of hardened gelatin. Attach it to the muzzle of a bolt action .22, and put a 0-30 psi air pressure gauge on the side of the bottle. Fire a round into the gelatin, and record the pressure on the gauge before the hot gases cool too much.

My speculation is that up to a pint of extra gas will be injected into the pop bottle, and the pressure will rise by less than 15 psi.

Anybody tried something like this? Any handloaders have any estimates of the volume increase of the powder from solid-to-gas upon firing the .22?

Thanks for any feedback.

Henry

But Why?

interesting.....so how do we use this data to improve our shooting.....or is it merely data collected because we can?

The pressure and volume are directly proportional

PxV = PxV

I am not too sure that a 2 liter bottle with hold 15 PSI. On the other hand after the pressure wave passes and equilibrium sets in I bet the pressure is less than 5 PSI but it leak back around the fired case pretty quick.

Did I post this on the wrong Forum? I thought that there might be a "rule-of-thumb" something like "1 cc of smokeless powder gets converted intn 1500 cc of hot gas"--or something like that.

Thanks, Henry

Thanks, Ireload2. I didn't see your post before my reply. You are right: maybe I should video the gauge when I shoot. Another formula used in "gas generator" work is PV=nRT. The T what produces the uncertainty: it is the temp degrees K. While still burning in the cartridge the T is one thing, but I expect T has reduced a lot before it hits the bottle because the gas is expanding.

Oh, Ireload2, the 2-liter pop bottles fail at about 100-150 psi. There are some youtube's out showing "carbon dioxide bombs" with gauges, and they all explode near this pressure. It is also a curiosity to me that they never fail at a seam, but rather get blown into lots of parts: they fragment.

PETE is tough stuff but I would not want to be around 150 PSI when it pops. I have seen car tires that were burst the same way but took about 300 PSI.

BTW my estimate was based on a 20 inch barrel with the pressure at the muzzle having dropped to 1000 PSI. I suspect it is lower than that though.

quote:

Originally posted by Henry22LR:
Did I post this on the wrong Forum? I thought that there might be a "rule-of-thumb" something like "1 cc of smokeless powder gets converted intn 1500 cc of hot gas"--or something like that.

Thanks, Henry

A .22 rimfire is almost out of gas when the bullet exits. If you knew the average pressure you might make a stab at the volume produced.

Ireload2, I think you may be right. A .22LR starts slowing down inside the barrel after the first 16 inches, they say (that is for subsonics, maybe, but it is a place to start). So I'll assume a constant acceleration on a 40 grain bullet and I should be able to come up with a pressure behind the bullet. Increase it by 1/3 for barrel friction. That MIGHT get me in the right ballpark.

Yeah, those Co2 bombs are NASTY. I used to work at an ice-house where they sold dry ice. Around quitting time some of the boys would get frisky, and once they threw a 2-liter bomb up on top of the building. Shook the whole place. Maybe about like two M-80's.

Next time I find a balloon laying around I'll pull a bullet from a 22LR and stretch the baloon over the end of a barrel. It may burst the ballon from the violence but hopefully it will give some sort of indication to the volume.

A while ago the kids and I did an experiment with a 1 liter bottle-bomb. I used chlorine pool shock and rubbing alcohol. If you search videos, there is one called "bottlebomb" or something where an idiot puts it into a bottle and shakes the bejessus out of the bottle, and of course it obliges by going off in his hand. Anyway, didn't want that to happen to me so I left a bit of space in the bottle by squeezing the sides in about an inch, figuring if it started fizzing or whatever I'd at least have a half second to toss it. Well I filled it and nothing happened so we gently put it down and went in the house. About 30 seconds after I put it down it went off with a teriffic bang, as was said pretty close to M80 in sound. (anyway, once was enough for me and the kids so it's one less worry I have to think about with them!)

quote:

Originally posted by Mark:
Next time I find a balloon laying around I'll pull a bullet from a 22LR and stretch the baloon over the end of a barrel. It may burst the ballon from the violence but hopefully it will give some sort of indication to the volume.

Good idea but wouldnt the hot gasses from the powder melt the latex of the balloon and cause it to pop? and also if it dosent have a very high PSI wont the balloon contract untill the barrel is full of gas first, by that i mean the balloon pushes some gas back in the barrel

Knowing the checmical composition of the powder - most likely double based nitrocellulose and nitrogylgerine - would allow you one to calculate the gaes generated by mass and thenc onvert to volume based on the density of nitrogen formed.

Also remember that the someless powder doesn't techically burn i.e. combine with oxygen- it decomposes into nitrogen, carbon, and maybe some nitrous oxides and CO2 or such. Black powder on the other hand actually burns the charcoal and sulfur utilizing the oxygen in the postasium nitrte.

The physics of what goes on inside a rifle barrel are pretty interesting. I was always curious as to why it was so difficult to drive a bullet much over 4000 fps regardless of the bullet weight and amount of powder used. I was messing around with one engineering program on flow and started plugging in numbers for pressures and temperatures I had read occur inside a rifle barrel. It turns out that choked flow - a point where the speed of the gas is equal to the speed of sound and can not flow any faster regardless of the pressure - occures around 4000 - 4500 fps! I was never able to confirm that is what actually occures but I never found a better explaination either.

It is fun to use your technical knowledge on your hobby. I'm a control systems engineer by trade and occasinally get involved in high pressure flow in refineries and chemical plants.

The gas would cool so quickly that the pressure would not change much. You could take the various gas components and calculate their partial pressure at ambient.
When I was a kid (long time passed) I fired a 22 under water expecting to see bulbles, didn't happen.
Good Luck!

/

16 inch barrel=40.64 cm=0.4064 meters

diameter=0.223 inch=0.55642 cm , radius=0.0028321 meter , area=0.00002519 sq meters

barrel volume=0.6246 cubic inches

bullet velocity=1050 fps=320 meter/sec (subsonic)

bullet clears barrel in 2.54 milliseconds This comes from formula S=1/2*a*t^2.

acceleration=0.126 million meters/sec/sec or 12,847 g’s

bullet weight=40 grains=2.592 grams= 0.002592 kilograms

F=mass*acceleration: F= 0.002592*0.126*1,000,000=326.6 newtons

Pressure=force/area=326.6/0.00002518=12970293 Nt/square meter=

12 970 293 newton/square meter = 1 881.181 957 917 234 pound/square inch

12970293 Pascal (newton/sq m) = 1,881.182034 lbf/square inch (PSI)

This pressure sounds low, but what the heck…

P1 * V1 = P2 * V2 , V2= P1*V1 / P2 = 1881*0.6246 / 14.7 = 79.92 cubic inches.

Backing up a little, and using British (American) units: The bullet area is about 0.039 square inches. With 1,881 psi behind it, that means 73.43 pounds pushing a bullet that weighs about 0.00571 pounds. This should yield an acceleration of about 12,861 g’s. Each g is worth 32.2 fps, or about 414,138 feet/sec/sec. Velocity=acceleration*time, and the bullet is under acceleration for 0.00254 sec (2.54 ms) for a muzzle velocity of 1052 fps. So it all works out…

I’ve still ignored barrel friction. The .22LR round is so tiny, it has a higher surface/volume ratio, so a higher part of its surface is in contact with the barrel than other rounds. Also, seems like “barrel lubes†aren’t real popular herebouts. So I guess I’ll stick with the above estimate of 80 cubic inches of gas generated, but remember that it might be low by maybe even a factor of 2.

So, if I filled my 2 liter pop bottle half full of incompressible gelatin, that would leave 1 liter filled with 14.7 psi air before each shot. One liter is 61.02 cubic inches. Into that I’m shoving ANOTHER 80 cubic inches minimum. That would raise the pressure in the bottle by a factor of (61+80)/61, or 2.31. Thus the new pressure would be 2.31 times the old pressure of 14.7 psi, or 33.97 psi. My gauge reads “0†at 14.7 psi, so after the shot would read about 19.3 psi. If barrel friction raises the generated gas necessary to 160 cubic inches, my final gauge reading would be 38.6 psi.

I didn't have a baloon but I used a surgical glove with a pistol. Other than putting a circular powder burn on the glove it barely even moved the glove, and there was no appreciable expansion of the glove volume.

I'll try it again when I come up with a baloon, but I think I'll try it with something heavier, like an '06 so that I can get some expansive gasses in action.

There is a problem using a plastics soft drink bottle - they stretch under pressure.

The measurement of gas volume produced would be taken at standard atmospheric temperature and pressure. Perhaps some sort of self-sealing valve could be used to hold the pressure in the bottle.

How about this one;
Seal the case in front of the rim with a small O-ring, fit a steel canister with a bullet trap, onto the muzzle with an O-ring type fitting and of course the pressure gauge. The total volume of the 'system' would have to be known. One can look up in the pressure tables to determine the added volume of gas that causes a specific rise in pressure, once the temperature has normalised.

Other than the fun of trying to measure it ourselves, we could contact the manufacturers of the propellant and ask them. It would be fun to see how close we can get!

The CB Long just makes sub sonic gas at 24" of barrel. [unlike 22" that makes a loud BANG]

That threshold is ~ 1 atmosphere above ambient.

PV= NRT, says that pressure is proportional to N.

The added gas would be an additional barrel full at one atmosphere.

V = pi r square L = 3.14 [.223/2]^2 24 = 1 cubic inch of gas.

The 2 atmospheres of pressure means that there would be 2 cubic inches of gas if reduced to 1 atmosphere of pressure.

Of course that volume is only good for the gas temperature at the time of bullet exit.

quote:

Originally posted by tnekkcc:
That [subsonic] threshold is ~ 1 atmosphere above ambient....

that is quite the statement right there. are you sure about it?

Tenekkcc, I used a 16 inch barrel, and got 0.6246 cubic inches as barrel volume, so 1 cubic inch of barrel volume is about right for a 24 inch barrel.

Then I calculated the psi necessary in that 16 inch barrel to get the bullet to 1050 fps using constant acceleration. It came out as 1,881 psi. So just as the bullet leaves, the whole barrel is filled with 1881 psi gas. If this existed at the same temperature at one atmosphere, it would occupy 1881/14.7 barrel full’s, or about 80 cubic inches.

You said, “The CB Long just makes sub sonic gas at 24" of barrel. [unlike 22" that makes a loud BANG]†This is very interesting. I’m pretty much STUCK right now: I have no way of knowing how this 80 cubic inches of hot gas empties out of the barrel once the bullet is gone. Maybe Tvfinak can help: he mentioned he has access to some flow programs.

Where does your quotation above come from? Maybe (hopefully) a URL?

If anyone can find a formula for smokeless powder -- what we want is the molar mass of it, and the reaction that it undergoes. With the molar mass, we can determine how many moles are in 2.2 grains of powder -- with the formula, we can determine how many moles are released -- I think it would be pretty easy to assume that while they'll be some residue left behind, everything else should turn into a product similar enough to an ideal gas. We could then use the ideal gas rule (PV=nRT) to calculate the volume at any temp and pressure

quote:

Originally posted by delloro:

quote:

Originally posted by tnekkcc:
That [subsonic] threshold is ~ 1 atmosphere above ambient....

that is quite the statement right there. are you sure about it?

I noticed the threshold phenomena by at least 1995.
I had taken EE360 acoustics in college in 1977, but could not figure out the mechanism.
I asked around the internet, but Randy Ketchum, a gunsmith who never went to college, figured out the mechanism by 1999.
By 2004 someone had calculated the pressure for me.


In 1995
http://groups.google.com/group/rec.guns/browse_thread/t...bd2/e806fcd90d2c1a20
1999
http://groups.google.com/group/rec.guns/browse_thread/t...3dd/45413253c3f636ca
2004
http://groups.google.com/group/rec.crafts.metalworking/...b55/5aab4dc266ba7c50


What does it all mean?
A CB Long produces WAY less gas than a normal 22 cartridge, but it is one I can calculate.

quote:

Originally posted by Henry22LR:
Tenekkcc, ....

Then I calculated the psi necessary.. using constant acceleration. It came out as 1,881 psi.

Don't use constant acceleration.
If I put a 36 gr friction proofed bullet in quickload for 22 rimfire long rifle experimental, with 1.3 gr AA#2 and a 24" barrel, I get 1200 fps, peak pressure is 13kpsi, which is about right.
The muzzle pressure is 26 BAR.
That would be ~26 cubic inches of gas.
1/2 of the velocity is reached in the first inch of barrel.

What does it all mean?
I would need a 312" barrel to make the 26 cubic inches of gas quiet with a regular 22LR cartridge.
It would be much easier to use a suppressor can of the same volume 2" inches in diameter and 8" long.

"Don't use constant acceleration.
If I put a 36 gr friction proofed bullet in quickload for 22 rimfire long rifle experimental, with 1.3 gr AA#2 and a 24" barrel, I get 1200 fps, which is about right.
The muzzle pressure is 26 BAR.
That would be ~26 cubic inches of gas.
1/2 of the velocity is reached in the first inch of barrel. "

I have no problem with that, tnekkcc. I only assumed constant acceleration to make the math easier. What you are saying is that the .22 bullet gets a BIG boost in velocity early on, and by the end of the 24†barrel the barrel pressure is “only†382.2 psi (26 BAR) not the 1880 psi I had predicted using constant acceleration.

Is that muzzle pressure (26 BAR) measured, or calculated?

**********

I’m not ignoring you, Aglifter, I just can’t find a molecular weight for smokeless powder. Not even for nitrocellulose, which I thought would be easy. Apparently nitrocellulose cross-links into longish chain molecules…

Did you find a structure for nitrocellulose -- shakes head, at one time I would have probably been able to tell how nitrous acid attacks cellulose -- If I can remember things I was taught long ago, I might be able to figure out, roughly, how much gas is liberated

quote:

Originally posted by Henry22LR:


Is that muzzle pressure (26 BAR) measured, or calculated?

That is calculated with Quickload, which is often within 1/2 percent on bottlenecked rifle velocities and off by 1000 % on on pressure for hot rodded straight wall pistol cartridges.

After reading all the above and contemplating the meaning of life, I think I will go take a nap.

quote:

Originally posted by tnekkcc:
...
By 2004 someone had calculated the pressure for me.

2004
http://groups.google.com/group/rec.crafts.metalworking/...b55/5aab4dc266ba7c50

that link does no more than to state, without foundation or explanation, that:

"I read somewhere that the theoretical pressure required for air to reach Mach 1 when exhausting into standard atmosphere was only 13 PSI gauge.
Presumably, even with less than optimum nozzle geometry, it wouldn't take a lot greater pressure to guarantee that part of the stream is then supersonic."

That is, scientifically speaking, a "ginormous" assumption and does not prove the point. I will experimentally disprove it tomorrow, by uncorking a 20 psi air hose and listening for the .22-like crack and the po-po to arrive at my home in a residential, quiet area.

Nothing in that thread calculated anything.

quote:

Originally posted by Aglifter:
If anyone can find a formula for smokeless powder --

wikipedia has a formula: C6H8(NO2)2O5

Thanks, delloro: assuming that is the correct chemical formula, now we need the temperature in the rifle barrel to apply PV=nRT.

As a friend always reminds me,"...it's always SOMETHING".

quote:

Originally posted by delloro:

quote:

Originally posted by tnekkcc:
...
By 2004 someone had calculated the pressure for me.

2004
http://groups.google.com/group/rec.crafts.metalworking/...b55/5aab4dc266ba7c50

that link does no more than to state, without foundation or explanation, that:

"I read somewhere that the theoretical pressure required for air to reach Mach 1 when exhausting into standard atmosphere was only 13 PSI gauge.
Presumably, even with less than optimum nozzle geometry, it wouldn't take a lot greater pressure to guarantee that part of the stream is then supersonic."

That is, scientifically speaking, a "ginormous" assumption and does not prove the point. I will experimentally disprove it tomorrow, by uncorking a 20 psi air hose and listening for the .22-like crack and the po-po to arrive at my home in a residential, quiet area.

Nothing in that thread calculated anything.

If you can get a more accurate supersonic gas threshold pressure imperially, I would appreciate the datum.

imperially? if I could imperially order up data, I wouldn't be spending my time here.... more to the point, I don't have any empirical data (not even one datum) to offer, at least not beyond my 15 p.s.i.g. air hose test. which did not produce a sonic "crack." since you you don't, either, them we are back without a simple formula for determining the loudness of a .22 LR round.

now, the difference in absolute pressure before and behind a sonic shockwave may be 14-ish p.s.i.g., but there are *so many* other variables involved in forming and maintaining that differential, that a simple value does not suffice. the force neede to create and maintain the sonic shockwave is more than a static guage differential in 14 p.s.i.

I thought it was reasonable to accept that the threshold of supersonic gas is near one atmosphere, as the maximum amplitude of a sound wave would be +/- one atmosphere, clipping the bottom of the wave with cavitation.
As the expanding gas ball slows to subsonic, a sound wave propagates at that amplitude, with the frequency content falling off with wavelengths longer than this size of the ball at threshold.

What does is all mean?

Because the sound wave can't get any louder than 2 atmospheres at the top peak and a vacuum at the bottom peak, it is safe to assume that the threshold pressure for making the loudest sounds is about one atmosphere above ambient.

The problem is that the sound waves in the barrel are not propagating as “linear†waves, but as “nonlinear†waves. I don’t understand it as much as I should, but what happens is that the traveling waves heat the gas as they travel through it. The next waves through are then traveling in a hotter gas, and waves travel faster in a hotter gas. GOOOGLE “shock tubes†and they will have some pictures.

A common phenomena is called “sawtoothingâ€. The waves actually climb up on one another, and instead of remaining a nice sine wave, start to build very rapidly-falling wavefronts called shock wavefronts. The pressure profiles start to look like a sawtooth wave, and get more and more “sawtoothy†as the measuring apparatus is moved downrange of the source.

This might help explain the appr. 4,000 fps upper limit on bullet velocity.

With an smaller cartridge insert with shorter barrel in a shotgun, the waves can travel down the large barrel and pass up the subsonic bullet. The shotgun barrel acts much like a wave guide for electro magnetic micro waves, with attenuation at frequencies with 1/2 wave lengths longer than the bore diameter.

Other than that, the barrel is just a high pressure vessel until the bullet un corks it.
Then the barrel acts as a pressure source with an output impedance controlled by the bore diameter.
That pressure and source impedance then creates the supersonic gas ball.

I think I see the confusion. the 1 atm. difference between the leading and trailing edges of a sonic boom wave is not the same as having an instantaneous 1 atm. pressure source to generate the wave. one needs much, much more than 1 atm. pressure being released from a tube to create a transonic event with a 1 atm differential. there is a lot of dissipation of force and energy between the "uncorking" and the formation of the shock wave.

The time it takes to accelerate a gas is the same at the uncorking as in each wave length of propagation sound that alternates between compression and acceleration.

What does it all mean?
Neither gas acceleration is instantaneous.
What is needed is a fast uncorking, like a bullet, and not your thumb on a gas tube.

The book “Firearms, the Law and Forensic Ballisticsâ€, by Tom A. Warlow offers a work of reference on the forensic science of firearms. It describes what happens when a weapon is fired in terms of internal, external and terminal, or wound, ballistics...

http://books.google.com/books?

Mr. Warlow is a reloader, using Hercules doubl-base powder, and a .308 rifle. A little of the text of his book is shown at the above URL. For example,Page 103, “3 grams Hercules (alliance) 15 double-base smokeless powder produces up to 11,961 joules of kinetic energy in a rifle projectile. “

I expect that one of the contributors to this Forum, having read the above URL, could add significantly to our discussion in this Thread

I'm still trying to get a good number on the volume of gas produced by a subsonic 22LR round.

That URL is not it. Please copy the proper URL from between the quotation marks her and paste it into your Address line, followed by "enter":


“http://books.google.com/books?id=YkcvshsGhagC&pg=RA1-PA103&lpg=RA1-PA103&dq=%22internal+ballistics%22+basics&source=web&ots=mDFMVawRdI&sig=ARNbBNtaMOmWhTJi79gOYJARy_0"

http://www.the-long-family.com/shock%20wave%20theory%20...ry%20explanation.pdf

Here is a VERY good article on barrel resonance and a model of how it affects accuracy. It touches on some things people on this Thread have alluded to. An easy read, too. About 17 pages long.