GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: billzweig on October 25, 2019, 10:59:01 PM
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This is a first test of the prototype, not quite an air-gun yet. In this design I am trying to obtain higher velocity by eliminating the complex air path found in most guns and by releasing the projectile only with the full air pressure behind it (in a regular design the projectile starts moving as the pressure builds up thus increasing the volume)
The design is using an high voltage discharge to trigger the process. In my experimental setup it is quite a big circuit, but can be significantly reduced in size. I will show more details soon.
youtu.be/3bh1qDong58
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nice.. I see a capacitor and some nicad batteries in there. Im assuming its an electric dump valve of your own creation .. Is it a pilot system , is it venting gas to fire ?? cool either way and impressive with such a small volume of air
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Interesting concept.... How long is the barrel?.... I assume air, not Helium?....
Bob
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I this a PCP or is the pressure made by the "high voltage discharge"? If the latter, then this is essentially a firearm, not an airgun. Right?
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Nifty!
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nice.. I see a capacitor and some nicad batteries in there. Im assuming its an electric dump valve of your own creation .. Is it a pilot system , is it venting gas to fire ?? cool either way and impressive with such a small volume of air
I am preparing a full description of the system. The electrical discharge (400V, 400uF) is triggered by 30KV spark gap.This is only one way to trigger and I do have two other options I shall describe.
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Interesting concept.... How long is the barrel?.... I assume air, not Helium?....
Bob
Yes, compressed air. The barrel is 32" long and is really the weakest part of the system. I've made it myself and I am not that happy with it. I think I can get better results with a Lothar Walther barrel, but I did not manage to get one from them.
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Nifty!
Thanks
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I this a PCP or is the pressure made by the "high voltage discharge"? If the latter, then this is essentially a firearm, not an airgun. Right?
Not quite. The propellant is compressed air, not chemicals. The high voltage just triggers the release.
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You are achieving greater efficiency than I have ever seen.... The maximum possible FPE, which is based on the energy input, can be calculated as follows:
Bore area (sq.in) x pressure (psi) x barrel length (ft.)…. That is (0.45 x 0.45 x PI/4) x 4000 x (32 / 12) = 636 lbf. acting through 2.67 ft. = 1698 FPE....
That assumes a constant 4000 psi over the entire barrel length (which requires a reservoir of infinite volume)…. and that 1700 FPE includes the energy of the air being accelerated as well.... The mass of air in your barrel at 4000 psi is 25.2 grams (based on a density of 0.3024 g/cc at 20*C)…. That means the air weighs more than your bullet.... Logically, achieving 1300 FPE out of a possible 1700 would be pretty difficult under those circumstances.... Typically, a very good PCP does not achieve even 50% of the theoretical maximum, ie 850 FPE would be an excellent result....
I will be looking forward to seeing how your system works.... I suspect that your peak pressure may be well over 4000 psi because of the energy of the spark discharge raising the temperature.... the combined energy giving the boost you are seeing... Just my current thoughts.... I've been wrong before.... :-[
Bob
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Plasma discharge can go to 45000 degrees! Might be a small :o pressure jump from that! :P
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i am watching with extreme interests.
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Does anyone mentionned the volume of air the valve contained?? The video show better working of any inline valve.. Thanks for sharing..
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Very interesting that is a lot of power being made. I am awaiting the description.
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I remind you it takes energy to accelerate a projectile.
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Are you compressing ambient air or pure oxygen?
Pure oxygen is explosive.
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Energy does not come from nothing, couple of Joules from the capacitor at best, spark in range of nano seconds does not heat the air so much.
Burst disk in very critical pressure and opening a piezo valve to let more air in could work, or using the arc to rupture the disk is another.
Interesting to see how this unfolds.
Marko
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I must apologize. There is an error in the results of the test. I've recovered one of the spent bullets and realized I was using lighter bullets for the test. I've machine those bullets in small batches of various sizes and the 23 grams was mixed with the 18.5 grams bullets. So the weight used in the video was 18.5 gram (293 grain). Consequently the energy is 1055 ft/lbf (1430 Joules).
Please forgive me. I was away from the shop for some time and eager to start the testing. And in some way fooled myself by the excitement. I will make anew video - including all the technical details - to replace the current one.
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thats still really impressive as texan users strive to fall 200 fpe lower than that.
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So the weight used in the video was 18.5 gram (293 grain). Consequently the energy is 1055 ft/lbf (1430 Joules).
850 FPE would be an excellent result....
So, still impressive, Bill. Thanks for sharing your efforts.
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Uploaded a new video:
https://www.youtube.com/watch?v=hnmhKNyoKlQ (https://www.youtube.com/watch?v=hnmhKNyoKlQ)
This one includes a link to full details.
I am sorry if I was a bit secretive and did not show all the information initially. Maybe now, that it is all disclosed, it does not look that interesting anymore. I doubt very much if this has any commercial value, but I did apply for a US patent (provisional) . I am afraid this will be the worst investment of USD70.00
At this stage of development I am looking at ways to reduce the consumption of the air and some easy way of ejecting the spent disk.
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Uploaded a new video:
https://www.youtube.com/watch?v=hnmhKNyoKlQ (https://www.youtube.com/watch?v=hnmhKNyoKlQ)
This one includes a link to full details.
I am sorry if I was a bit secretive and did not show all the information initially. Maybe now, that it is all disclosed, it does not look that interesting anymore. I doubt very much if this has any commercial value, but I did apply for a US patent (provisional) . I am afraid this will be the worst investment of USD70.00
At this stage of development I am looking at ways to reduce the consumption of the air and some easy way of ejecting the spent disk.
I know next to nothing about what you are doing, but GOOD ON YOU for applying for the patent!
Now to watch the video and see if I understand anything... (chuckle)
Thanks for posting it Bill!
OK, so the "high voltage discharge" destroys the rupture disk to fire the shot?
If that isn't it, then I am still lost. (chuckle)
Thanks again!
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thanks for sharing. very interesting design.
there is a bit of concern about the projectile itself. the brass projectile will probably not be accurate due to the parting lines from the burst disk interfering with its aerodynamics in flight? and the lead projectiles’s base may get damaged from the burst disk just after the burst? maybe set a gap between the projectile and the disk?
i wish you can test this to 100 yards and show some accuracy results.
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be very interesting if the disc could be made from a material that completely submilates ( solid to gas ) during the firing process
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Interesting concept.... but I do have some questions....
1. What is the volume of 4000 psi air in the firing chamber?.... It appears that all 80cc of the 4000 psi air in that chamber is dumped during the shot, correct?....
2. The gun is simply laying on the table beside the electronics board when you press the trigger.... C-clamp noted :-[ , but still, where did all the recoil energy go?....
3. When you shot through the Chrony, which was only a few feet from the muzzle, the vertical support rods never even wiggled.... With all the air in that firing chamber being dumped, why is there no evidence of that huge mass of air passing through the Chrony?....
4. The report in the Video was extremely muted (ie VERY quiet)…. The noise of all that air being expelled, and the shock waves from the bullet going supersonic, should have been extremely loud.... Why is that not recorded?....
Bob
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i saw on the website he provided the chamber is 80cc.
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Bob you are not the only one making the same observations.
1000+fpe does shake things around some.
Marko
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Agreed, the gun would fly off the table if not secured, but I can see a big C-clamp at about 1:41 into the video securing the gun to the table.
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Billzweig, you are talking to people who have big bore airguns from 100 fpe up to 3000+ fpe power level. We know what happens.
Lloyd, yes I saw C-vise. But whole table would not be there.
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the audio is a non factor since almost all recording devices now level out loud disturbances.. the table has what appears to be 30-40 lbs of stuff residing on it , so i dont think the gun would toss the table backwards. as for the chrony not shaking , I cannot explain that but im sure Bill can.
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I agree, there are many loose ends on this, but I am still very curious about what Bill is working on. Vaporizing the burst disc is very interesting. The wind movement, etc, are missing, but as far as the sonic crack is concerned, when I took my 2131 and 2135fps shots with approx 7 grain aluminum pellets, releasing them in a manner not unlike the burst disk, my video camera didn't pick up a sonic crack. And I had ear muffs on and didn't hear much at all. I do remember my wife telling me from several "walls" away, that it was "LOUD."
Thanks for sharing this with us Bill.
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I am having some trouble reconciling the small 80cc chamber, connected to a barrel with a volume of 83.4 cc, being able to produce over 1000 FPE of energy.... You are starting with 4000 psi, but by the time the bullet reaches the muzzle, the pressure will have dropped to less than 2000 psi (using Isothermal expansion)…. and less than 1500 psi if the expansion is Adiabatic (which is more likely)…. That means that the simple "maximum FPE" calculation of 1700 FPE, which disregards the mass of the air and assumes an infinite reservoir volume (and hence a constant 4000 psi)…. grossly overestimates the possible FPE.... Bear in mind, the mass of air in that 80cc reservoir is 24.2 grams = 373 grains (heaver than the bullet)…. Using 1/3 of that mass as the mass being accelerated to the MV gives a rough estimate of the energy lost in accelerating the air.... That would be about 400 FPE.... These effects make achieving over 1000 FPE even more difficult.... particularly bearing in mind we rarely achieve 50% of the maximum FPE that is theoretically possible....
Yes, thanks for sharing, I enjoy seeing something new.... but there are a few things here I do not understand, and want to....
Bob
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It seems that this arrangement will immediately apply full pressure to the bullet, and most (all?) of the current valve designs do not facilitate this immediate pressure build up and maximum acceleration. So that is one important point, I think.
During the capacitor discharge that burns the disk, if the capacitor is charged to the full 420vdc and 420uF, then its potential could be 148 Joules. If that energy is all dumped, as an arc, in 1/10th of a millisec, then that power is 1.48 Mega Watt for .0001 seconds, or, in less dramatic terms, .041 watt hour. Personally, I like the 1.48 mega watt description, LOL. There will be energy lost in the external spark gap that needs to be subtracted. But all those Joules of spark right behind the bullet, ought to do something when arcing to, and burning, the Havar? Like a welder? Maybe?
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You bring up an interesting point, Lloyd.... I wonder if the temperature of the spark is high enough to induce combustion of the various metals in the Havar alloy disc at 4000 psi.... I suspect that when the rupture disc is vapourized, the tiny particles / atoms would easily be heated enough by the spark to combine with the Oxygen in the air and produce significant energy in the form of heat of combustion, and possibly some volume of a "metallic-oxide" gas as well.... The two combined could raise the temperature and pressure of the air and produce extra acceleration for the bullet.... If this were to take place, the energy input to the system from such combustion could easily exceed the 148 Joules of the spark itself.... If this is the mechanism that is taking place, caution is suggested, less the pressure spike exceed or compromise the safety limits of the containment system....
I tried to find a bit of useful information on this process using Google.... but all I came up with was a Thesis investigating the use of nano-aluminum particles in alcohol, water, or pure oxygen, as a boost in energy for rocket fuels.... :o
Incidently, if the metal disc is "burning" and adding power to the system.... by legal definition it becomes a firearm in the USA.... Since it is over 500 fps, it already is, in Canada.... ::)
Bob
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Since I am not exactly sure what is going on inside during operation, I think it is still a PCP, at least for now. Maybe a hybrid later, LOL. Would the arc be a plasma arc, And what does that mean in regards to energy output? This is new territory for me, which of course makes it extra fun!
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Hey Bill,
It's cool that you're trying something new.
What I noticed was that the barrel doesn't seem to screw in very far, and at 1:10 I see sharp edges, burrs and no chamfers anywhere. That's the kind of stuff that gets my attention. What kind of material is the chamber made out of?
I wonder what the peak pressure is?
Good luck and thanks for posting this.
Steve
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For the sake of an academic argument, this experiment will help clarify if and how much heat is being added by the arc or combustion. Simply eliminate additional heat, or combustion by using an engineered full bore cold rupture disc:
Find or make a 4000 PSI burst disc. Install in the system without the capacitor charged. Aim the barrel at the backstop over the crony and fill slowly with air pressure until the burst disc blows from over pressure.
Firing needs to happen at 4000 PSI, so a series of burst discs may need to be constructed, starting with 3000 PSI to ensure the rupture pressure VS thickness is understood.
Now; compare the projectile velocity obtained with a 4000 PSI cold rupture disc against that obtained with the hot rupture disc.
What makes this a potentially bad idea is if the burst disc does not rupture at 4000 PSI and there is no other way to fire or depressurize the system... There must be a safe way to bleed the system, else a system that sits on the point of failure at 4000 PSI is a big problem. After a period of material creep, or a slight increase in storage temperature, then boom...
I would imagine that such a rupture disc as I describe above would not just be made from thin aluminum or brass shim stock (something that won't hurt the bore), but that there would be a sharp "scored" anular ring to make it rupture in such a manner that the free disc can pass down the barrel in predictable fashion. A definite stress raiser that functions a bit like the notch in a Charpy Test specimen...
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EDITED (Thanks Matt)
Yes, the video was replaced with this one:
https://www.youtube.com/watch?v=hnmhKNyoKlQ (https://www.youtube.com/watch?v=hnmhKNyoKlQ)
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If that was the first video he removed it because he used a slug at a much lighter weight then first described giving a false representation.
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3. why is there no evidence of that huge mass of air passing through the Chrony?....
4. shock waves from the bullet going supersonic, should have been extremely loud
Well, the backstop board can be seen moving back and forth after every shot. Just look at the hole next to the chrony wires (top left) - video starts at that time stamp: https://youtu.be/hnmhKNyoKlQ?t=131
Audio recording equipment often makes gun shots sound "quiet". This one has a bit of a crack to it, although not "impressive sounding".
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If that was the first video he removed it because he used a slug at a much lighter weight then first described giving a false representation.
Matt, I think you must have missed Bill's explanation, 3 days ago, of his mistake with the weight of the bullet.
Lloyd
I must apologize. There is an error in the results of the test. I've recovered one of the spent bullets and realized I was using lighter bullets for the test. I've machine those bullets in small batches of various sizes and the 23 grams was mixed with the 18.5 grams bullets. So the weight used in the video was 18.5 gram (293 grain). Consequently the energy is 1055 ft/lbf (1430 Joules).
Please forgive me. I was away from the shop for some time and eager to start the testing. And in some way fooled myself by the excitement. I will make anew video - including all the technical details - to replace the current one.
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If that was the first video he removed it because he used a slug at a much lighter weight then first described giving a false representation.
Matt, I think you must have missed Bill's explanation, 3 days ago, of his mistake with the weight of the bullet.
Lloyd
I must apologize. There is an error in the results of the test. I've recovered one of the spent bullets and realized I was using lighter bullets for the test. I've machine those bullets in small batches of various sizes and the 23 grams was mixed with the 18.5 grams bullets. So the weight used in the video was 18.5 gram (293 grain). Consequently the energy is 1055 ft/lbf (1430 Joules).
Please forgive me. I was away from the shop for some time and eager to start the testing. And in some way fooled myself by the excitement. I will make anew video - including all the technical details - to replace the current one.
I most certainly did not miss that bit which was why I was trying to get at with my post for the removed video...
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Lloyd,
Matt was helping set me straight with his video reference. Thanks to both of you.
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For the sake of an academic argument, this experiment will help clarify if and how much heat is being added by the arc or combustion. Simply eliminate additional heat, or combustion by using an engineered full bore cold rupture disc:
Find or make a 4000 PSI burst disc. Install in the system without the capacitor charged. Aim the barrel at the backstop over the crony and fill slowly with air pressure until the burst disc blows from over pressure.
Firing needs to happen at 4000 PSI, so a series of burst discs may need to be constructed, starting with 3000 PSI to ensure the rupture pressure VS thickness is understood.
Now; compare the projectile velocity obtained with a 4000 PSI cold rupture disc against that obtained with the hot rupture disc.
What makes this a potentially bad idea is if the burst disc does not rupture at 4000 PSI and there is no other way to fire or depressurize the system... There must be a safe way to bleed the system, else a system that sits on the point of failure at 4000 PSI is a big problem. After a period of material creep, or a slight increase in storage temperature, then boom...
I would imagine that such a rupture disc as I describe above would not just be made from thin aluminum or brass shim stock (something that won't hurt the bore), but that there would be a sharp "scored" anular ring to make it rupture in such a manner that the free disc can pass down the barrel in predictable fashion. A definite stress raiser that functions a bit like the notch in a Charpy Test specimen...
Subscriber, I like that idea.
A couple of ideas to help alleviate your concern about the safety of the cold rupture disk might be:
1. Testing of the rupture disk could be done without any bullets loaded, so no danger of a berserk slug taking off unannounced.
2. The burst disk could be scored in a pie wedge pattern, and a pointed mechanical pin could be used to puncture it to initiate failure when the 4000 psi pressure was reached. Hopefully, the leaves would lay out flat against the barrel bore and not exit the barrel.
A while back I had tried machining some projectiles with a thin wire-like retainer that secured them in the breech. The projectile had an o-ring so that it held air like a cork held back by a string. I never did get one to break at the desired pressure. Lloyd
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I agree, you can see the backstop move a bit with each shot impact.... I am still bothered by not seeing any significant air blast, however.... I have fired a PCP enough times at 550 FPE to know just how violent that is.... We are talking twice that FPE, and a dump shot of 1350 std. CI of air to boot.... :o
I'm sure Bill will answer my questions when he has a chance....
Bob
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I am still bothered by not seeing any significant air blast...
The muzzle to chrony distance appears to be 4 feet. Long enough for the typical condensation cloud to dissipate?
Certainly, that slug should able to go through as much pine board as a mild .44 mag revolver load...
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I'm not talking about a condensation cloud.... I have blown the diffusers clear off a Chrony at 3-5 feet from the muzzle at 550 FPE just from the air blast, and not from a dump shot, but quite an efficient one from a .45 cal.... Even at 10 feet, the diffusers and the support wires wobble all over the place.... :o
Bob
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Even at 10 feet, the diffusers and the support wires wobble all over the place.... :o
Maybe at 10 feet the air blast is wide enough to hit the crony supports and screens, but a 4 feet it passes through between them :)
Fair question. While there may be jumbo shrimp; there are no pocket nukes...
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You didn't read this fact, stated above....
I have blown the diffusers clear off a Chrony at 3-5 feet
I'm not stating that the OPs claims are incorrect.... just that they do not fit with my experience, or knowledge of Physics as it relates to airguns.... I have stated many, many times that when presented with irrefutable, empirical data that conflicts with the theories we currently use.... it is time for a new theory/explanation that will encompass those results.... This may well be one of those times.... ;)
At one time, there was a supposedly well understood theory that you could not exceed 1650 fps with a PCP, based on the concept that is the average speed of random air molecules at room temperature, so air could not expand faster than that.... We threw that theory away when Lloyd hit over 2100 fps with a purpose built test gun.... and I confirmed it by doing nothing more than putting a 1.8 gr. plastic Airsoft BB in my 6mm PCP, and averaged 2092 fps for 3 shots....
Assuming the test results in the video are accurate and repeatable.... the logical thing to do is to explore where the additional, unexpected energy may be coming from.... If further tests prove that the spark, and any associated burning/vapourization of the rupture disc is not the source.... then a true breakthough can be claimed.... Subsequent to that, then we will have to figure out why.... 8)
Bob
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Even at 10 feet, the diffusers and the support wires wobble all over the place.... :o
Maybe at 10 feet the air blast is wide enough to hit the crony supports and screens, but a 4 feet it passes through between them :)
Fair question. While there may be jumbo shrimp; there are no pocket nukes...
No it wont, I had chrony on tripod just 2 feet in front of the gun and it fell down at only 300 fpe.
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there are only 80cc worth of air moving towards the chronograph. and there is a muzzle brake cut out in front of the barrel.
maybe that 80cc of air gets cut in 1/3rd so maybe there is only 55cc moving towards the chrono? i am just guessing.
anywho, dont think Bill is responsive to those speculations. maybe we need to find out on our own
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80 cc @ 4000 psi = 22 litres…. which is over 3/4 cu.ft…. :o
My Hayabusa .457 releases half that much air in a max. power (550 FPE) shot.... and let me tell you, if you have a Chrony 4 feet away it will rock it all over the place, and usually blow the screens off.... and sometimes knock it over completely.... ;)
I don't see any muzzle brake, threads maybe?....
Bob
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Sorry for not replaying sooner. Heath issues again and no work or even computer for the last week. Seems that curing one issue can upset other....
Let me try and answer some of the questions. I must admit the results did surprise me as well. Since then I have had only two chances to to run tests with the rupture propagated simply by gradual pressure increase with the electrode removed. The burst pressure was bout 3500 psi for the bras cartridge and another one one with the lead cartridge and cemented (stainless this time) disk about 4000. The chronograph missed the reading on that one but the brass cartridge, some 13 gram (200 grain) without the flange, clocked only 850 f/sec (259 m/sec).
So, friends, I am just as puzzled as you are. It is quite possible that the actual spark has something to do with it especially since there is was fair amount of grease on the orings and consequently on the foil. By itself it might not be a bad situation if it works to increase the energy.
I have noticed as well another issue. With the test shown in the video there were little fragments of the peat moss dispersed all around. With the brass bullet I did not have the peat moss bag (I placed it as to stop any ricocheting slugs, But since those in the previous tests either went clean through the 2x10 or got deeply embedded. I did not have it in the last test. I am wondering if some of this flaying debris could have been affecting the chronograph. Still, the slug seemed very powerful in one occasion penetrating the moss and the board and the other getting deeply embedded partly sticking out through the other side of the board (that is how I've discovered my error in the projectile mass). Forgive my arrogance and showing only the through hole...
As for the recoil of my setup I did take precautions and the whole thing was well braced with a huge weight on the bottom of the cart added in the last minute. In fact the recoil was less than feared. As for the sound level it was very high, probably higher than any air gun I have heard, however the camera (Sony NEX 7) was facing away and the sharp spike probably somehow equalized by the camera recording system.
There is a lot to test. All the tests must be repeated many times and evaluated. As well I want to change the setup and to space the "gun", the chronograph and the target - it was easy just to place it all near the door of my gas storage room where my high pressure air pump is plumbed permanently as well. There is as well the issue of easily ejecting, preferably automatically, the spent disk. For the record I should add that the actual calibre is 11.12mm or 0.438". This is a result of past attempts (years ago) at making my own barrels using shop made rifling button that ended to be undersized and consequently reaming the bore to this size before rifling. Altogether the barrel is poor and my intention is to get a Lothar Walther for next tests.
As it is, for now I will have to abandon the development and deal with the health issues and some family problems that have emerged recently. Thank you for the comments and interest.
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This is an unintentional post, pressed the wrong button. Sorry
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Bill, it is always interesting when someone and something new comes along.... Spend your time recuperating, and we look forward to your return and continuing results.... I'm glad you took the questions in the spirit they were intended, and not as criticism....
Bob
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I this a PCP or is the pressure made by the "high voltage discharge"? If the latter, then this is essentially a firearm, not an airgun. Right?
I don't know anywhere near as much as Bob (rsterne) or the OP about what is going on here, but I think this would at least fall into a hybrid category as a mix of firearm and PCP airgun.
As my quoted post above suggested, there is "high voltage discharge" or "fire", so there is most likely combustion. How much, I don't know, but there is some I am sure.
Does this combustion account for the added pressure/velocity? I don't know, but it is the most likely candidate.
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.
I am not trying to derail this thread or discourage the OP from his testing and all my best to the OP concerning his health problems!
Just thinking and rambling...
Kerry
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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:
https://www.youtube.com/watch?v=8Dd_qiuWxPs (https://www.youtube.com/watch?v=8Dd_qiuWxPs)
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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?
I have no real knowledge of how compressed air combusts, but given there is a fire source, I would think the oxygen in the compressed air is the real source of fuel.
I thought about the combustion engine angle, but forgot to add that to my comment. (grin)
P.S.
It is also firing a projectile. No combustion piston engine is "supposed" to do that. Right?
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I would think the oxygen in the compressed air is the real source of fuel.
By definition; oxygen is the oxidizer that takes the reducing agent's (fuel) electrons.
You need three things for combustion:
Fuel
Oxidizer
Activation energy of sufficient magnitude.
Activation energy required can be reduced by means a catalyst (as in catalytic converter); or by increasing the pressure. That is why pure high pressure oxygen is so dangerous. You don't need to increase the temperature of 3000 PSI oxygen to start combustion, with a fuel such as oil or grease present.
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I would think the oxygen in the compressed air is the real source of fuel.
By definition; oxygen is the oxidizer that takes the reducing agent's (fuel) electrons.
You need three things for combustion:
Fuel
Oxidizer
Activation energy of sufficient magnitude.
Activation energy required can be reduced by means a catalyst (as in catalytic converter); or by increasing the pressure. That is why pure high pressure oxygen is so dangerous. You don't need to increase the temperature of 3000 PSI oxygen to start combustion, with a fuel such as oil or grease present.
What is the temperature of the "high voltage discharge"? Could that be of "sufficient magnitude"?
Anyway, the only thing that stands out, at least to me, to account for any added velocity is the possibility of combustion via the "high voltage discharge" which I assume creates a fairly high temperature, even if only for a very short time.
I'll go back to just lurking on this thread, as I really don't have the knowledge or understanding that some do here. ;)
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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.
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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:
https://www.youtube.com/watch?v=8Dd_qiuWxPs (https://www.youtube.com/watch?v=8Dd_qiuWxPs)
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.
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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:
https://www.youtube.com/watch?v=8Dd_qiuWxPs (https://www.youtube.com/watch?v=8Dd_qiuWxPs)
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
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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.
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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...
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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.
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Look at how much energy there is in a teaspoon full of petrol:
https://www.youtube.com/watch?v=gfr3_AwuO9Y&feature=youtu.be&t=207 (https://www.youtube.com/watch?v=gfr3_AwuO9Y&feature=youtu.be&t=207)
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...
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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...
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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.
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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?
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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.
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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.
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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.
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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
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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 (http://www.shippai.org/fkd/en/cfen/CB1012038.html)
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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.
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There is still one ramaining problem with that video. Chrono does not move at all, not one pixel.
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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 (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.
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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
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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.
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My reference that it might be considered a firearm relates solely to the BATF definition.... I agree it's an airgun, with the possibility it is getting a boost in power from some form of combustion or heating initiated by the spark in a 4000 psi container.... The fuel could be an oil mist, tiny particles of metal, or even vapourized metal, I don't know, and don't really care....
The bottom line is that the shots in the video show more power than I would expect from that pressure, bore and barrel length.... It is interesting that when Bill did a test where he simply let the disc fail from increasing pressure, he only got about 470 FPE at 3500 psi.... well within "normal" parameters for a .438 cal with a 32" barrel.... In fact, I wouldn't bat an eye until the FPE for that pressure went over 700 FPE, which is the 50% of maximum level we sometimes see in top notch PCPs....
Bob
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420 V
4.20E-04 F
=
37.044J
E=1/2*C*V^2
420uF at 420V stores 37 Joules of energy. Most of that discharge becomes heat inside the airgun. Maybe 1/4 of that could be added to the projectile velocity? I estimate +7 ft-lbs max, not more and probably less. Not enough to cause a significant difference.
One issue that concerns me is how well the discharge circuit is constructed and shielded. I used to design Pulse Power circuits and the EMI/EMP from pulsed discharges usually disrupted any measurement devices within 20'-30'. Special grounding and shielding of both the discharge circuit and the measurement devices was necessary to get any valid event data. If a computer was part of the data collection, a fully shielded room (Faraday Cage) was needed or the PC would lockup or reboot from the impulse.
I wonder if the Chronograph is getting EMI'd showing a false faster velocity during the electronic trigger and a more realistic slower velocity during the passive (not electrically triggered) burst disc test?
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I don't know enough to comment on whether an EMI could affect a Chrony.... but it's as good a theory as any other, IMO....
Bob
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It seems likely that the higher energy is related to the spark mode of triggering. I did not consider any side effects like this and the spark simply seemed like an elegant way to trigger the gun. In the actual gun design the discharge is entirely confined in the bolt and thus fully shielded. The cross sectional drawing is showing the 30KV trigger electrode (12) concentric with the main electrode (13). I did bench test this configuration and it works well.
When I shall return to this project (certainly hoping...) I'll try the following:
1. New, commercial barrel. Possibly 9mm.
2. Comprehensive testing of the electrically triggered vs mechanical or pressure buildup
3. Intentional introduction of combustible particles (oils and similar) into the air charge
4. A new "receiver" with adjustable pressurized air volume to determine the optimum one.
Again, thank you all for the comments and suggestions. Much appreciated.
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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.
The indicating gauge was installed only to verify the initial charge pressure. Not only it peeks at 4000, but it is highly damped (by a small orifice in the gauge air passage: a set screw with a 0.3mm hole drilled through it) to prevent gauge damage during the burst.
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I wonder if the Chronograph is getting EMI'd showing a false faster velocity during the electronic trigger and a more realistic slower velocity during the passive (not electrically triggered) burst disc test?
Michael, Looks like your comments got everybody thinking.
I happened to have a DIY electric fence charger handy (don't laugh, it is not pretty, but it works) that can easily make a 10mm spark. Bringing the Chrony's control unit or its connection wire anywhere close to the spark gap does something. Bill, I realize that this chrony and setup are quite different from yours, but something might be going on.
Bill, if you need a barrel blank, TJ's in Alexandria KY has an extensive selection. PM me if you need his barrel specs list or contact information.
Lloyd
https://youtu.be/-HLiOeajByo
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This comes under the heading of "Leave it to Lloyd" to figure out how to test something nobody ever though of.... ::)
Well done, buddy.... 8)
Bob
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Bill, looking at your nicely detailed drawing, I don't understand the air path.... You are probably aware of the necessity of having a plenum (firing chamber) of large enough volume to provide the necessary air for the shot.... In a conventional, regulated PCP, we find that about 1 cc of HPA per FPE you intend the gun to produce is a good value to keep the pressure during the shot from dropping too much.... Decreasing the plenum to 1/2 cc per FPE will require about a 10% increase in regulator setpoint to make up for the additional pressure drop.... This means that high powered PCPs need a very large plenum.... This is why you don't see regulators on many Big Bore PCPs....
Dump valves, such as you are building, are slightly different, in that we usually look at the valve volume (HPA to be dumped) as a percentage of barrel volume.... Generally speaking, once the valve volume exceeds half the barrel volume the efficiency goes into the dumper.... You are running a dump chamber about the same as the barrel volume (0.438 x 0.438 x PI/4 x 32) = 4.82 CI = 79 cc.... Here is what happens to the pressure during the shot for a few valve volume percentages, starting with 4000 psi:
Valve is twice barrel volume.... pressure at bullet exit = 2667 psi.... average pressure = 3333 psi....
Valve equals barrel volume.... pressure at bullet exit = 2000 psi.... average pressure = 3000 psi....
Valve 50% of barrel volume.... pressure at bullet exit = 1333 psi.... average pressure = 2667 psi....
Valve 25% of barrel volume.... pressure at bullet exit = 800 psi.... average pressure = 2400 psi....
If we assume that the average pressure, times the bore area (which is the average force), times the barrel length in feet, divided by 2 (to allow for losses), is the approximate FPE.... we get the potential FPE = (0.438 x 0.438 x PI/4 x 32 / 12 / 2) x average pressure.... which is the barrel volume (in CI) / 24 x avg. press.... Your barrel volume is 4.82 CI, so that divided by 24 is 0.201.... If you had an unlimited plenum, and therefore a constant 4000 psi, that works out to (0.201 x 4000) = 804 FPE.... As the average pressure decreases because you have a limited volume to dump, you get the following....
Valve is twice barrel volume, FPE = (0.201 x 3333) = 670 FPE
Valve equals barrel volume, FPE = (0.201 x 3000) = 603 FPE
Valve 50% of barrel volume, FPE = (0.201 x 2667) = 536 FPE
Valve 25% of barrel volume, FPE = (0.201 x 2400) = 482 FPE
To determine the approximate efficiency, we divide the potential FPE by the volume of air used, in standard CI, which is the pressure in bar times the valve volume.... We would get the following....
Valve is twice barrel volume (9.64 CI x 276 bar) = 2660 CI.... Efficiency is (670 / 2660) = 0.25 FPE/CI
Valve equals barrel volume (4.82 CI x 276 bar) = 1330 CI.... Efficiency is (603 / 1330) = 0.45 FPE/CI
Valve 50% of barrel volume (2.41 CI x 276 bar) = 665 CI.... Efficiency is (536 / 665) = 0.81 FPE/CI
Valve 25% of barrel volume (1.20 CI x 276 bar) = 332 CI.... Efficiency is (482 / 332) = 1.45 FPE/CI
Now these are only vague approximations, but it lets you see what happens to the FPE and the efficiency as you change the valve volume as a percentage of barrel volume.... I hope that gives you some insight into the volume of the dump reservoir you need, and how changing it will potentially affect the FPE and the efficiency....You can see the reason that dump valves seldom exceed 50% of the barrel volume.... the small gain in FPE is usually not worth the extra air used to produce it....
Bob
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This comes under the heading of "Leave it to Lloyd" to figure out how to test something nobody ever though of.... ::)
Well done, buddy.... 8)
Bob
Thanks Bob,
But ya know, that really shows how well shielded my plain vanilla Samsung android phone is. It was able to record video and audio with no noticeable effects from the spark. But the chrony processor box, or the cable going to it, certainly picked up some EMI.
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Decreasing the plenum to 1/2 cc per FPE will require about a 10% increase in regulator setpoint to make up for the additional pressure drop....
You can see the reason that dump valves seldom exceed 50% of the barrel volume.... the small gain in FPE is usually not worth the extra air used to produce it....
So, rather than doubling the plenum volume, double the starting pressure (if possible)? Or, is a higher starting pressure so much more efficient that you only need to increase it by 10% to have the same effect as doubling the plenum volume, dumped at the lower starting pressure?
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Is EMI related to the spark voltage or quantity of charge dumped? The spark generating coil must be exceeding 10kV, while the capacitor dumped to initiate the burst disk is operating only at 400 volts. Perhaps the 30 kV trigger is interfering more than Lloyds transformer.
The electrical discharge (400V, 400uF) is triggered by 30KV spark gap.
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Is EMI related to the spark voltage or quantity of charge dumped? The spark generating coil must be exceeding 10kV, while the capacitor dumped to initiate the burst disk is operating only at 400 volts. Perhaps the 30 kV trigger is interfering more than Lloyds transformer.
The electrical discharge (400V, 400uF) is triggered by 30KV spark gap.
Speed of a discharge, the rate of current change over time = di/dt, is related to how much EMI is generated. That means the sparkgap circuit IS more likely to generate interference. The ignition coil in the video uses a fast di/dt to generate a high voltage impulse. The resulting spark radiates significant EMI which is nicely shown messin' with the Chrony. Cell phones are designed to send and receive very high frequency EM waves. While they are not bullet-proof to EMI (don't arc directly TO the phone!), they will usually function closer to EMI sources that shut down other less robust electronic devices.
I see a similar problem when TIG welding on equipment with electronics attached or nearby. The TIG high frequency arc starter function (basically a small Tesla Coil) has to be disabled or I run the risk of frying some critical electrical controls.
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[/quote]
Bill, if you need a barrel blank, TJ's in Alexandria KY has an extensive selection. PM me if you need his barrel specs list or contact information.
Lloyd
Thanks. But I am not sure how easy it is importing a gun barrel to Canada.
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I am not sure how easy it is importing a gun barrel to Canada.
Contact Bob Sterne via PM. As a fellow Canadian, and a custom airgun builder, he probably knows all pertinent laws and channels: https://www.gatewaytoairguns.org/GTA/index.php?action=pm;sa=send;u=2569 (https://www.gatewaytoairguns.org/GTA/index.php?action=pm;sa=send;u=2569)
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My reference that it might be considered a firearm relates solely to the BATF definition.... I agree it's an airgun, with the possibility it is getting a boost in power from some form of combustion or heating initiated by the spark in a 4000 psi container.... The fuel could be an oil mist, tiny particles of metal, or even vapourized metal, I don't know, and don't really care....
I'm reminded of an "Electrothermal gun" that had been posted to the spudfiles forum:
Some time ago i started building a fairly large capacitor bank that aim planing to use for my rail-gun project.
Its consist of 24, 15000uF 400v capacitors for a total energy of 28800 Joules.
The capacitors are arranged in 3 parallel banks that are wired in series for 1200v and 40000uF.
To test the capacitor bank i decided to build a ElectroThermal Gun.
The ETG (ElectroThermal Gun) works by discharging the capacitor bank threw fine aluminium powder and foil inside a chamber.
The electric current then heats the aluminium enough to make it evaporate and turn into plasma.
When the aluminium turns into superheated plasma it expands and the pressure in the chamber increases, the plasma also heats the air so it expands.
The expanding gases then force the projectile down the barrel like a conventional (spud)gun.
The ETH have a 12mm smooth-bore barrel that is screwed into a steel chamber with a electrode that goes threw a insulator in the end, the power is then feed into that electrode and threw the aluminium-powder.
Some videos.
Test shot 1:
http://www.vimeo.com/751433 (http://www.vimeo.com/751433)
Test shot 1, Second view:
http://www.vimeo.com/751469 (http://www.vimeo.com/751469)
Test shot 2:
http://www.vimeo.com/751476 (http://www.vimeo.com/751476)
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Bill, looking at your nicely detailed drawing, I don't understand the air path.... You are probably aware of the necessity of having a plenum (firing chamber) of large enough volume to provide the necessary air for the shot.... In a conventional, regulated PCP, we find that about 1 cc of HPA per FPE you intend the gun to produce is a good value to keep the pressure during the shot from dropping too much.... Decreasing the plenum to 1/2 cc per FPE will require about a 10% increase in regulator setpoint to make up for the additional pressure drop.... This means that high powered PCPs need a very large plenum.... This is why you don't see regulators on many Big Bore PCPs....
Dump valves, such as you are building, are slightly different, in that we usually look at the valve volume (HPA to be dumped) as a percentage of barrel volume.... Generally speaking, once the valve volume exceeds half the barrel volume the efficiency goes into the dumper.... You are running a dump chamber about the same as the barrel volume (0.438 x 0.438 x PI/4 x 32) = 4.82 CI = 79 cc.... Here is what happens to the pressure during the shot for a few valve volume percentages, starting with 4000 psi:
Valve is twice barrel volume.... pressure at bullet exit = 2667 psi.... average pressure = 3333 psi....
Valve equals barrel volume.... pressure at bullet exit = 2000 psi.... average pressure = 3000 psi....
Valve 50% of barrel volume.... pressure at bullet exit = 1333 psi.... average pressure = 2667 psi....
Valve 25% of barrel volume.... pressure at bullet exit = 800 psi.... average pressure = 2400 psi....
If we assume that the average pressure, times the bore area (which is the average force), times the barrel length in feet, divided by 2 (to allow for losses), is the approximate FPE.... we get the potential FPE = (0.438 x 0.438 x PI/4 x 32 / 12 / 2) x average pressure.... which is the barrel volume (in CI) / 24 x avg. press.... Your barrel volume is 4.82 CI, so that divided by 24 is 0.201.... If you had an unlimited plenum, and therefore a constant 4000 psi, that works out to (0.201 x 4000) = 804 FPE.... As the average pressure decreases because you have a limited volume to dump, you get the following....
Valve is twice barrel volume, FPE = (0.201 x 3333) = 670 FPE
Valve equals barrel volume, FPE = (0.201 x 3000) = 603 FPE
Valve 50% of barrel volume, FPE = (0.201 x 2667) = 536 FPE
Valve 25% of barrel volume, FPE = (0.201 x 2400) = 482 FPE
To determine the approximate efficiency, we divide the potential FPE by the volume of air used, in standard CI, which is the pressure in bar times the valve volume.... We would get the following....
Valve is twice barrel volume (9.64 CI x 276 bar) = 2660 CI.... Efficiency is (670 / 2660) = 0.25 FPE/CI
Valve equals barrel volume (4.82 CI x 276 bar) = 1330 CI.... Efficiency is (603 / 1330) = 0.45 FPE/CI
Valve 50% of barrel volume (2.41 CI x 276 bar) = 665 CI.... Efficiency is (536 / 665) = 0.81 FPE/CI
Valve 25% of barrel volume (1.20 CI x 276 bar) = 332 CI.... Efficiency is (482 / 332) = 1.45 FPE/CI
Now these are only vague approximations, but it lets you see what happens to the FPE and the efficiency as you change the valve volume as a percentage of barrel volume.... I hope that gives you some insight into the volume of the dump reservoir you need, and how changing it will potentially affect the FPE and the efficiency....You can see the reason that dump valves seldom exceed 50% of the barrel volume.... the small gain in FPE is usually not worth the extra air used to produce it....
Bob
Thank you, Bob, for the really nice calculation. In the test setup I have used an air volume about equal to the volume of the barrel. The volume behind the projectile was charged to 4000 psi ( directly from the air tank using the tank valve) and then fired.
The gun drawings are really jut conceptual. Item 25 is the pressurized air admitting valve and in this concept a manual valve. It can be a needle valve for controlled filling to the desired pressure, of a larger orifice valve allowing quick fill by, say, pressing a 1/4 turn spring return lever. The air (communicating with the air bottle by passage 26) passes through the circumferential gap 24 confined by seals 16 and 17 and fills the volume 14. In the drawing none of this is the final size or volume. The barrel will probably be (if ever built...) smaller calibre and the bolt volume adjusted accordingly.
In this concept I am assuming that either the user fills the bolt volume manually to his/her desired pressure, or the bottle is equipped with a pressure regulator for constant, one touch fill.
The way I see the operation of the gun is:
1. Load the "belted" bullet
2. Close the bolt
3. Fill the bolt chamber (slow needle valve of "instantaneous" one touch)
4. Start the capacitor charging by the holding the back trigger on the pistol grip or optional other switch. This take about 5 seconds on fully charged NiCad battery and once the voltage is reached the circuit cycles to keep the charge.
5. Fire by closing the trigger switch
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I am not sure how easy it is importing a gun barrel to Canada.
Contact Bob Sterne via PM. As a fellow Canadian, and a custom airgun builder, he probably knows all pertinent laws and channels: https://www.gatewaytoairguns.org/GTA/index.php?action=pm;sa=send;u=2569 (https://www.gatewaytoairguns.org/GTA/index.php?action=pm;sa=send;u=2569)
Thanks!
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Is EMI related to the spark voltage or quantity of charge dumped? The spark generating coil must be exceeding 10kV, while the capacitor dumped to initiate the burst disk is operating only at 400 volts. Perhaps the 30 kV trigger is interfering more than Lloyds transformer.
The electrical discharge (400V, 400uF) is triggered by 30KV spark gap.
Speed of a discharge, the rate of current change over time = di/dt, is related to how much EMI is generated. That means the sparkgap circuit IS more likely to generate interference. The ignition coil in the video uses a fast di/dt to generate a high voltage impulse. The resulting spark radiates significant EMI which is nicely shown messin' with the Chrony. Cell phones are designed to send and receive very high frequency EM waves. While they are not bullet-proof to EMI (don't arc directly TO the phone!), they will usually function closer to EMI sources that shut down other less robust electronic devices.
I see a similar problem when TIG welding on equipment with electronics attached or nearby. The TIG high frequency arc starter function (basically a small Tesla Coil) has to be disabled or I run the risk of frying some critical electrical controls.
I am familiar with electromagnetic pulse effect on electronics, but in my tests the chrono did not respond at all to repeater pulses. The air gap is only about 1mm and most the discharge confined inside the gun. But thanks for the comments and thanks for the ignition coil video. I will investigate it again.
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I'm reminded of an "Electrothermal gun" that had been posted to the spudfiles forum
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Impressive, but hardly portable.
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I want to thank you all for this lively discussion. Once I get back to this project, hopefully some of the unknowns shall become clear.
But today I've arrived to town (Vancouver, BC), to a hospital tomorrow morning... and a hope of a quick return to my rural home. I am not much of a city person.
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I want to thank you all for this lively discussion. Once I get back to this project, hopefully some of the unknowns shall become clear.
But today I've arrived to town (Vancouver, BC), to a hospital tomorrow morning... and a hope of a quick return to my rural home. I am not much of a city person.
Bill, we hope things go well for you, and that have a good recovery. Did you bring a lap top or sketch pad or something in case you have an "ah-ha!" moment, or several, while away from home?
Lloyd
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I'm reminded of an "Electrothermal gun" that had been posted to the spudfiles forum:
The ETH have a 12mm smooth-bore barrel that is screwed into a steel chamber with a electrode that goes threw a insulator in the end, the power is then feed into that electrode and threw the aluminium-powder.
So, is that like a thermite reaction in an enclosed space? ???
I gotta have one of those! :P
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So, is that like a thermite reaction in an enclosed space? ???
Thermite requires iron oxide powder/aluminum powder mix. It burns hot enough to melt steel. As such, barrel life might be a bit short :).
The way it was explained, the energy release is not from oxidizing the aluminum powder, although with air, some of it must surely burn. It was explained, as if it is vaporizing the metal, and using that increase in volume and pressure, like a steam engine uses water.
Speaking of which; if you simply dumped a lot of heat into a small volume of water, it would turn to steam and drive a projectile, just fine. While waiting for the shot, that water would need to be kept in a water tight membrane of sorts. Else, it would corrode the metal parts.
https://www.youtube.com/watch?v=5uxsFglz2ig (https://www.youtube.com/watch?v=5uxsFglz2ig)
https://www.youtube.com/watch?v=zkph_NNC73g (https://www.youtube.com/watch?v=zkph_NNC73g)
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So, is that like a thermite reaction in an enclosed space? ???
I gotta have one of those! :P
The same builder obtained some much better results with highly pressurized air/propane mixes in an enclosed space, like penetrating 10mm steel plate (https://i.imgur.com/ednESP0.jpg):
https://vimeo.com/1445056 (https://vimeo.com/1445056)
I digress however, this is beyond the scope of this forum and I don't want to hijack Bill's thread. The build thread is here (http://www.spudfiles.com/hybrid-cannon-database/topic15524.html) if you want more information.
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There is no question that combustion of a fuel of some kind increases the performance.... and the working pressures.... of a firearm.... Designing around those pressures, especially if you don't know that they are.... is something I have no interest in experimenting with.... HPA is dangerous enough, thanks....
Bob
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x 2
Lloyd
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im shocked no one has built a home tinkerer light gas gun.. Basically one of these steel spud guns slamming a piston into high pressure helium .. Now that would be interesting . ( and only fatal for the user half the time
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There is no question that combustion of a fuel of some kind increases the performance.... and the working pressures.... of a firearm.... Designing around those pressures, especially if you don't know that they are.... is something I have no interest in experimenting with.... HPA is dangerous enough, thanks....
Bob
Bill should consider being further away from his test rig, or have a hard barrier between himself and it, as if it is expected to "pop".
"It was more powerful than I thought, but did not blow up in my face", is not a good strategy. Only once the system is fully understood can one move towards trusting it enough to think of a shoulder fired version. Obviously, this is just a lab set-up to prove a principle, but the overriding principle is to beware unintended consequences.
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Hi again. Have been away for some time; health issues and other vicissitudes of life. Thank you all for the comments and the interest.
I did no further work on this project, though I do hope to in the near future. My first step will be changing to 9mm and getting a proper barrel. As well I would like to switch to a mechanical initiation of the rupture foil using a sharp "firing pin", solenoid driven.