1300 Foot Pounds large bore airgun

[billzweig]

Uploaded a new video:



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.

[BackStop]

Uploaded a new video:



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!

[darkcharisma]

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.

[Rob M]

be very interesting if the disc could be made from a material that completely submilates ( solid to gas ) during  the firing process

[rsterne]

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

[darkcharisma]

i saw on the website he provided the chamber is 80cc.

[MJP]

Bob you are not the only one making the same observations.
1000+fpe does shake things around some.

Marko

[lloyd-ss]

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.

[TPL]

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.

[Rob M]

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.

[lloyd-ss]

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.

[rsterne]

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

[lloyd-ss]

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?

[rsterne]

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.... 

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

[lloyd-ss]

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!

[Machinist]

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

[subscriber]

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]

EDITED  (Thanks Matt)

Yes, the video was replaced with this one:

[Insanity]

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.

[subscriber]

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: 

Audio recording equipment often makes gun shots sound "quiet".  This one has a bit of a crack to it, although not "impressive sounding".