1300 Foot Pounds large bore airgun

[subscriber]

It is also firing a projectile.   No combustion piston engine is "supposed" to do that.  Right?

That is why it is called a disposable piston. 

Just because a projectile may be fired by means of a fuel or propellant does not mean the ATF has interest in regulating it:  Consider black powder muzzle loaders and cartridge weapons made before 1899 are not regulated in the USA.  These are only regarded as firearms by law when brandished, or used in a crime.

Now, if you are having too much fun with a given technology, then I can see a segment of the population and their pet politicians wanting to regulate or ban it: 

About 10 years ago I was on vacation in South Africa, and happened to read a newspaper article about the "need to ban spring air rifles".  It was claimed that part of their power came from burning lubricant, and thus they should be treated as illegal unregistered firearms.  The guys on this forum that use inert lube to eliminate all dieseling might provide a counter argument, but I digress.

[billzweig]

If this is true, then the BATF would, IMHO, probably classify this as a firearm and not an airgun.

One could argue that there is no "explosive" (as per BATF definition of a firearm) involved, but if there is combustion there is fuel.

Why not declare it a single cylinder, disposable piston, internal combustion engine?   

I don't think the ATF recognizes sheet brass as a propellant or accelerant; or even a fuel.  Metal powder, yes.  Solid bits that you could not light with a match, no. 

Perhaps the burst disc is acting as a "heating coil", transferring the stored energy in the capacitor to the compressed air volume:  Acting both as a resistance and as a heat exchanger. 

Melting the disc turns part of it into metal vapor and metal droplets, with lots of surface area.  This should be effective for heat exchange and oxidation.  If these particles or vapor are being burnt, where are the products of combustion?  Is there any of it left on the remainder of the burst disc that can be examined?

Anyway, the ATF has no jurisdiction in Canada.  If it did, declare this project govt research and get them to pay for it.  Sure, a few permits and licenses might be required...

Sometimes it is just a matter of how you classify things that counts:

All this is still too far in the future - if anything will come of it in the first place. At the time of building the rather crude electrical setup I did test the effect of the discharge on foils. The discharge is sometimes creating a tiny hole in the foil, often just a little crater. There is definitely heat generated, though not much heat and most of it local on an are of less than millimetre square (some dissipated in the air gap).
Another though came to my mind today. The two runs shown in the video were with freshly pumped air cylinder. It took about 20 minute to bring it to full pressure before the first shot and it was upped to the full pressure for some 4-5 minutes for the second. The test with the brass projectile was done with the tank already filled for a few days. I have noticed that the pump is producing quite a lot of oil mist that enters the cylinder. Can it be that I was igniting a mixture of atomized oil and air? In the dense atmosphere of 4000 psi air the mist can take along time to settle...
As with any experiment there are many unpredictable circumstances sometimes leading to a great discovery (for example the seemingly unimportant difference between wood and marble test tables that allowed Enrico Fermi to get a Nobel prize ) but more often show that the whole concept is wrong.

[BackStop]

If this is true, then the BATF would, IMHO, probably classify this as a firearm and not an airgun.

One could argue that there is no "explosive" (as per BATF definition of a firearm) involved, but if there is combustion there is fuel.

Why not declare it a single cylinder, disposable piston, internal combustion engine?   

I don't think the ATF recognizes sheet brass as a propellant or accelerant; or even a fuel.  Metal powder, yes.  Solid bits that you could not light with a match, no. 

Perhaps the burst disc is acting as a "heating coil", transferring the stored energy in the capacitor to the compressed air volume:  Acting both as a resistance and as a heat exchanger. 

Melting the disc turns part of it into metal vapor and metal droplets, with lots of surface area.  This should be effective for heat exchange and oxidation.  If these particles or vapor are being burnt, where are the products of combustion?  Is there any of it left on the remainder of the burst disc that can be examined?

Anyway, the ATF has no jurisdiction in Canada.  If it did, declare this project govt research and get them to pay for it.  Sure, a few permits and licenses might be required...

Sometimes it is just a matter of how you classify things that counts:

All this is still too far in the future - if anything will come of it in the first place. At the time of building the rather crude electrical setup I did test the effect of the discharge on foils. The discharge is sometimes creating a tiny hole in the foil, often just a little crater. There is definitely heat generated, though not much heat and most of it local on an are of less than millimetre square (some dissipated in the air gap).
Another though came to my mind today. The two runs shown in the video were with freshly pumped air cylinder. It took about 20 minute to bring it to full pressure before the first shot and it was upped to the full pressure for some 4-5 minutes for the second. The test with the brass projectile was done with the tank already filled for a few days. I have noticed that the pump is producing quite a lot of oil mist that enters the cylinder. Can it be that I was igniting a mixture of atomized oil and air? In the dense atmosphere of 4000 psi air the mist can take along time to settle...
As with any experiment there are many unpredictable circumstances sometimes leading to a great discovery (for example the seemingly unimportant difference between wood and marble test tables that allowed Enrico Fermi to get a Nobel prize ) but more often show that the whole concept is wrong.

Thank you Bill.   I was wondering about the possibility of oil/lubricant being a part of this equation.   Seems there is something combusting and adding the pressure.   The question is what?

Good luck with your health problems!

Kerry

[subscriber]

What is the temperature of the "high voltage discharge"?   Could that be of "sufficient magnitude"?

The current is raising the temperature of the burst disc enough to soften it near instantaneously, causing it to  rupture and release the air.  This suggest temperatures high enough to light a vaporized fuel, were that present in the air. 

If part of the metal disc is being converted to small molten droplets, these particles could start burning:  You might be amused to see how fine steel wool can be lit with a match, and that it burns about as fast and hot as kindling of similar "fiber" size.  And that is in air at ambient pressure.  Combustion is easier to initiate in high pressure air because the oxygen and fuel are forced closer together.  Burning also proceeds at a faster rate, further increasing the pressure and temperature.  So, such an exothermic reaction can boost itself.

[subscriber]

Can it be that I was igniting a mixture of atomized oil and air? In the dense atmosphere of 4000 psi air the mist can take along time to settle...

Obvious oil mist in high pressure air, with a small molten metal trigger could explain all of the "extra performance", actually.

Some might say you are lucky you did not blow up your pressure vessel, as a "doubled performance" suggests doubled pressure; as in 8000 PSI...

[BackStop]

Can it be that I was igniting a mixture of atomized oil and air? In the dense atmosphere of 4000 psi air the mist can take along time to settle...

Obvious oil mist in high pressure air, with a small molten metal trigger could explain all of the "extra performance", actually.

Some might say you are lucky you did not blow up your pressure vessel, as a "doubled performance" suggests doubled pressure; as in 8000 PSI...

I also wondered about oil residue that might combust given a high enough temperature and pressure?   Such as any oil residue left in the barrel, chamber, etc.

One relatively easy test would be to shoot this device in darkness or with a thermal camera (if available).

If there is combustion of a significant level, it might show up at the muzzle.

[subscriber]

Look at how much energy there is in a teaspoon full of petrol: 


Oil mist of equivalent volume may be harder to light, but it is just as energetic (diesel oil actually contains more energy than gasoline by volume).  So, who knows how much oil mist you had in your air tank.   Any amount of combustible oil is certainly something that is considered dangerous (due to spontaneous explosion hazard), in the realm of charging PCP airguns with high pressure air...

[subscriber]

If there is combustion of a significant level, it might show up at the muzzle.

A cloud of smoke and a burning oil smell are sure to be present, if oil mist combustion is occurring...

[billzweig]

What is the temperature of the "high voltage discharge"?   Could that be of "sufficient magnitude"?

The current is raising the temperature of the burst disc enough to soften it near instantaneously, causing it to  rupture and release the air.  This suggest temperatures high enough to light a vaporized fuel, were that present in the air. 

If part of the metal disc is being converted to small molten droplets, these particles could start burning:  You might be amused to see how fine steel wool can be lit with a match, and that it burns about as fast and hot as kindling of similar "fiber" size.  And that is in air at ambient pressure.  Combustion is easier to initiate in high pressure air because the oxygen and fuel are forced closer together.  Burning also proceeds at a faster rate, further increasing the pressure and temperature.  So, such an exothermic reaction can boost itself.

Yes, this can be one scenario, especially if my hypothesis about oil mist in the air is correct. I think that what initiates the busting of the disk (unless it is a pinhole where it is obvious) is some erosion of the metal at the spot of the spark. And yes, any spark on metallic surface will produce little molten metal droplets. This is quite visible for example in a burned fuse where the metal is deposited on the glass tube.
Wen I get my health and family issues back in order (if ever...) I shall return to more pragmatic testing. In any case I think the "integral burst element" projectile - a kind of belted cartridge - does have some potential in increasing the velocity or reducing air consumption in conventional air guns. One thing I would like to do one day is to convert an existing big bore air gun to accommodate those belted projectiles and to see the results.

[BackStop]

What is the temperature of the "high voltage discharge"?   Could that be of "sufficient magnitude"?

The current is raising the temperature of the burst disc enough to soften it near instantaneously, causing it to  rupture and release the air.  This suggest temperatures high enough to light a vaporized fuel, were that present in the air. 

If part of the metal disc is being converted to small molten droplets, these particles could start burning:  You might be amused to see how fine steel wool can be lit with a match, and that it burns about as fast and hot as kindling of similar "fiber" size.  And that is in air at ambient pressure.  Combustion is easier to initiate in high pressure air because the oxygen and fuel are forced closer together.  Burning also proceeds at a faster rate, further increasing the pressure and temperature.  So, such an exothermic reaction can boost itself.

Yes, this can be one scenario, especially if my hypothesis about oil mist in the air is correct. I think that what initiates the busting of the disk (unless it is a pinhole where it is obvious) is some erosion of the metal at the spot of the spark. And yes, any spark on metallic surface will produce little molten metal droplets. This is quite visible for example in a burned fuse where the metal is deposited on the glass tube.
Wen I get my health and family issues back in order (if ever...) I shall return to more pragmatic testing. In any case I think the "integral burst element" projectile - a kind of belted cartridge - does have some potential in increasing the velocity or reducing air consumption in conventional air guns. One thing I would like to do one day is to convert an existing big bore air gun to accommodate those belted projectiles and to see the results.

Bill, have you noticed a difference in velocity when the disk only has a pinhole and is not completely destroyed?

[billzweig]

If there is combustion of a significant level, it might show up at the muzzle.

A cloud of smoke and a burning oil smell are sure to be present, if oil mist combustion is occurring...

There might have been some smoke, though since I was not looking for it, I would probably not notice. Ditto for smell. And there was already smell of oil from running the pump in the same space. If indeed there was a combustion it would be rather slow compared to the progress of the projectile down the barrel and it would more likely just keep the pressure high for a longer time rather than instantaneously increase it.

[BackStop]

If there is combustion of a significant level, it might show up at the muzzle.

A cloud of smoke and a burning oil smell are sure to be present, if oil mist combustion is occurring...

There might have been some smoke, though since I was not looking for it, I would probably not notice. Ditto for smell. And there was already smell of oil from running the pump in the same space. If indeed there was a combustion it would be rather slow compared to the progress of the projectile down the barrel and it would more likely just keep the pressure high for a longer time rather than instantaneously increase it.

Even when I had dieseling in my Crosman Fire, the main thing I noticed was the louder report.   Not always the smell or the smoke.   Although, sometimes I did notice all 3.

[billzweig]

Bill, have you noticed a difference in velocity when the disk only has a pinhole and is not completely destroyed?
[/quote]

Obviously I could not see what is happening during the actual discharge. The tests of the spark effect on the foil were conducted in open air on the bench with a little disk of foil forming one electrode and the sharp tungsten rod a few millimetres away forming the other electrode.
Yes, the report was very loud, but that will be expected.

[BackStop]

Bill, have you noticed a difference in velocity when the disk only has a pinhole and is not completely destroyed?

Obviously I could not see what is happening during the actual discharge. The tests of the spark effect on the foil were conducted in open air on the bench with a little disk of foil forming one electrode and the sharp tungsten rod a few millimetres away forming the other electrode.
Yes, the report was very loud, but that will be expected.

LOL!   I think we are both getting tired.   The question you didn't answer was if you noticed any "velocity" difference when the disk only had a pinhole and was not destroyed.

At those pressures/velocities, YES, I would expect it to be pretty loud whether combustion was happening or not.  (grin)

Thanks Bill!

Kerry

[TPL]

Bill, if you are having that much oil mist from your HPA compressor you should be very cautious. It could accrue into your SCUBA tank. I have some reading for you:

http://www.shippai.org/fkd/en/cfen/CB1012038.html

[subscriber]

If indeed there was a combustion it would be rather slow compared to the progress of the projectile down the barrel and it would more likely just keep the pressure high for a longer time rather than instantaneously increase it.

Agreed:  Just because the average pressure might double, does not have to mean that the peak pressure has to double.

[TPL]

There is still one ramaining problem with that video. Chrono does not move at all, not one pixel.

[lloyd-ss]

I certainly agree that any buildup of combustibles in the air system is cause for caution (and alarm).
This thread shows the need to be careful.
https://www.gatewaytoairguns.org/GTA/index.php?topic=163928.0
If there is a serious concern about oil, using nitrogen instead of air would eliminate the issue altogether.  But that is easier said than done. Unless you live in a big city or industrial area, finding nitrogen at higher than 2,000 psi might be  a problem.

[darkcharisma]

Can it be that I was igniting a mixture of atomized oil and air? In the dense atmosphere of 4000 psi air the mist can take along time to settle...

Obvious oil mist in high pressure air, with a small molten metal trigger could explain all of the "extra performance", actually.

Some might say you are lucky you did not blow up your pressure vessel, as a "doubled performance" suggests doubled pressure; as in 8000 PSI...

if it spiked to 8000psi. a camera placed next to the built in gauge should be able to catch the spike.

and this design is in no way considered a firearm. it is at best “related” to black powder if one wants to insist. but i couldn't go to discuss its a firearm in anyway. its silly to even think about it

[subscriber]

if it spiked to 8000psi. a camera placed next to the built in gauge should be able to catch the spike.

The pressure spike and release would occur so fast that the (damped) pressure gauge would not have time to react; at least not all the way to 8000 PSI.  If you mean that any upward needle twitch on firing would be sufficient evidence, then maybe. 

Remember, the (probable) ignition source involves rupturing the burst disc by partially melting it.  So, both the ignition trigger for a pressure rise and the escape path that drops the pressure would occur at the same time.  A second unheated burst disc, that vents to the outside, would react to such a pressure event, if it were engineered to burst at just over 4000 PSI.