GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: jackssmirkingrevenge on December 16, 2018, 07:33:42 AM
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Some stills from a 2013 Youtube video covering an air cartridge concept that apparently went nowhere, leaving them here for posterity. It appears to be an exhaust valve design with a spool piston piloted at the rear. This makes it a bit more complex than basic spool designs like the Inovairtech MAC (https://hardairmagazine.com/news/product-news/shooting-inovairtech-big-bore-air-rifles/) but the return is better flow and less effort on the part of the striker to actuate the cartridge. One wonders if there could be sufficient pressure to cycle a semi-automatic action.
(https://i.imgur.com/Jzrnykc.jpg)
(https://i.imgur.com/LZvRSmC.jpg)
https://www.youtube.com/watch?v=dD-RanLex2c (https://www.youtube.com/watch?v=dD-RanLex2c)
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The problem with any of these designs is that the volume is too small to get high FPE, even with a dump valve.... I get it that nobody cares about the efficiency.... and the idea of using a very small caliber will certainly help.... but the Inovairtech MAC was a bust (I believe the company is gone now)….
Having said that, if you have any details about the volume inside the cartridge and how that compares to the barrel volume.... I'm prepared to listen.... I'm also curious about the use of a jacketed bullet on air.... AFAIK it has never been done successfully except by sabot.... Is it the intention to launch the plastic sabot with it, and if so, how do you keep it straight in the bore?....
Bob
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I don't recall what the pressure is behind a 338 Lapua; an uncle who was big into Palma events once lectured me on the ins and outs of high-performance loads and I only recall snippets. Anyway, maybe if an air-cartridge like that one above approaches the pressures of a chemical propellant, we'll see some excitement, but as it stands, that a whole lot of extra complexity.
If the intention is to use a regular powderburner with air cartridges, I could see something like this working if the intent was lower energy shots; IE: a 338 Lapua chambered air-powered squirrel-rifle. But then your fighting a lot the aforementioned complexity as well as bringing in what Bob mentioned- jacketed bullets- that likely don't have enough energy to provide a good level of accuracy for the air charge. I could be way off mark, but when a guy or gal can shell out less than a thousand bucks and get a big-bore PCP as well as a small-bore "squirrel gun", the fiscal dynamics of the evolution will likely overcome the engineering excitement.
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Watching the video I see the early MACR!
;D
I'd think the plastic part stays with the cart. Much like the MACR carts I had? You could change the caliber of the carts by changing the front section.
Inovairtech was talking about a larger version of the Carts and Guns to use them at one time.
I probably should have kept that MACR just for a future rare gun reason.
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So is Inovairtech gone belly up ?
I was really hoping for that revolver pistol they where supposed to be developing .
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The web site just says under construction. Been like that for awhile now.
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I looked up the .338 Lapua Magnum, and the cartridge capacity is 7.4 cc.... so minus the guts inside maybe 6 cc ?.... If you built a .172 with a 30" barrel, that has a barrel volume of 12 cc, which would certainly work and have decent power.... If you filled the cartridge to 4500 psi, when the bullet emerged from the muzzle there would be about 1500 psi remaining, so 1/3 of the air is wasted.... Again, some people don't care about that, but the muzzle blast would be considerable.... With 1/3rd of the air left when Elvis leaves the building, there should be lots of pressure to cycle a semi-auto.... You just have to figure out how to capture it.... ;)
The key to making this idea work is to keep the caliber, and hence the barrel volume, small, so that you can get good performance on such a small quantity of HPA.... IMO that is where the MAC met it's downfall.... plus the internal passages in the MAC cartridge were too restricted, even for a .25 cal, let alone the .357 they were building....
I can see using this NOE bullet if you wanted to try this idea.... 26 gr. as a FN and about 25 as a HP....
(http://noebulletmolds.com/NV/images/N.O.E._Bullet_Moulds_172-26-HP_GC_BM2.Jpg)
Tofazfou was getting about 980 fps from an MRod with a 28" barrel running on 3000 psi.... Using Lloyd's spreadsheet, and a dump valve of 6 cc, you should get about the same with a 4200 psi fill, give or take.... 8) …. Muzzle blast would be about twice Ced's gun....
Bob
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The MACR wasn't too bad in .257
I had the .257 barrel and .357 barrel
Ends of the carts were easy to swap
It was a bit loud with no LDC. I have video of shooting it at 3000 PSI.
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Agree, I would keep this system for small bores, that's why I had big hopes for the .25 Revolver.
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https://www.youtube.com/watch?v=0IQIGM1ywfg (https://www.youtube.com/watch?v=0IQIGM1ywfg)
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I was also hoping for the lever action rifle to be developed, can see myself with a full bandoleer of .25 cartridges for both rifle and pistol :) :)
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If you'd seen the price of the carts you'd probably have had a very small bandoleer!
;D
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Bob has or had one of the carts from inovairtech. So he does have hands on with one.
;)
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I'll follow along since the math always excites me. One thing for certain: this will be a playtoy for those with more coin to spend.
I'm still not as keen on the complexity per cartridge; I've one too many incidences with HP air over the years (comes with being an A-Ganger at shore duty in a maintenance facility!)- call it a desire for the KISS principle.
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It was a fun toy to be sure. The fun ends when it becomes work!
Like the SMG .22? Lot's of work is involved. So I traded the MACR off.
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One way or another it is interesting design for future calibers .111-.133 at 12FPE . May be some preheating CO2 cartridges can help solve volume insufficiency ?
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The problem with any of these designs is that the volume is too small to get high FPE, even with a dump valve.... I get it that nobody cares about the efficiency.... and the idea of using a very small caliber will certainly help.... but the Inovairtech MAC was a bust (I believe the company is gone now)….
No doubt that for a given volume of air, dumping cartridge every time is going to give you less shots than a single reservoir with an efficient valve. Compare this to the MAC however, with caliber sized porting, pneumatic actuation and almost no dead space, the ft lbs for a given amount air is bound to be significantly higher.
Having said that, if you have any details about the volume inside the cartridge and how that compares to the barrel volume.... I'm prepared to listen.... I'm also curious about the use of a jacketed bullet on air.... AFAIK it has never been done successfully except by sabot.... Is it the intention to launch the plastic sabot with it, and if so, how do you keep it straight in the bore?....
It seems to me that the synthetic part is a cartridge component that seals against the breech and not intended as a sabot. As to whether the jacketed projectile is the intended ammunition or just a demonstrator we can only speculate.
I see various pros and cons with using cartridges, as mentioned before efficiency isn't one of the benefits, however all the pressure bearing components are in the cartridge. This multiplies the amount of seals that could leak and increases the cost, on the other hand any leaks are more accessible and relatively easy to fix.
It also allows the platform itself to be more simply made if necessary, the Brocock Fox single shot takedown rifle comes to mind:
(https://i.imgur.com/tssHL5X.gif)
I was really hoping for that revolver pistol they where supposed to be developing .
You and many others apparently, if you start to type "inovairtech" in google the first suggestion is "inovairtech revolver"!
I can see why too, the plans looked pretty sweet:
(https://i.imgur.com/hXZ9Mya.jpg)
That's another benefit of cartridges, you have more than a century of cartridge-fed firearm development to look to for inspiration when it comes to a platform.
Certainly emulating firearms is what makes them attractive in places where access to real firearms is limited, they were quite popular in the UK for example before the amount of people converting them to powder-burners.
Brocock's PPK style "Para" is a good example:
(https://i.imgur.com/yKoNYP6.jpg)
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the ft lbs for a given amount air is bound to be significantly higher.
It is possible I misunderstood you.... but if that statement is to say that a dump valve can produce more FPE for a given amount of air than a timed valve in a PCP with a much larger reservoir, it is incorrect.... It is pretty simple to understand why, because the pressure during the shot decreases rapidly from the small cartridge, compared to staying nearly constant until the valve closes when releasing the same amount of air from a much larger reservoir.... Not only are conventional PCPs more efficient, but the sooner you close the valve, the greater that efficiency....
All PCPs can operate with wide open ports, whether timed with a large reservoir, or a dump shot with a small one, so that part of the equation must be eliminated.... Yes, it is true that a cartridge system has virtually no wasted volume, and it's a good thing, because it has so little air available anyways.... The wasted port volume in a PCP will usually less than 1% of the reservoir volume, so that is the pressure drop you are looking at.... Compare that to the massive pressure drop during a shot you get with a small cartridge, and it is easy to understand why they lack relative performance....
If dump valves were more efficient, plenum volume would make no difference, in fact the trend would be reversed.... You would get more power from a smaller plenum by dumping it than by using less dwell with a larger one.... That is simply not the case....
Bob
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It is possible I misunderstood you...
That seems to be the case, the full sentence was "Compare this to the MAC however, with caliber sized porting, pneumatic actuation and almost no dead space, the ft lbs for a given amount air is bound to be significantly higher." - I was comparing this style of cartridge to the Inovairtech MAC cartridges.
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Got you.... THIS cartridge is better than the MAC.... I would agree with that....
Bob
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Concept for a mechanically locked pressure actuated air cartridge in the same vein as some airsoft 40mm grenades:
(https://i.imgur.com/XZyo5KK.gif)
By having the two o-ring diameters on the piston close to each other, differential pressure and therefore the amount of friction that resists the motion of the "firing pin" can be kept to a minimum, thus allowing for a possible blowback repeater.
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The only thing I question is the retention of the front O-ring on the valve piston.... You might be better to use a conventional poppet and seat arrangement at that point.... Just a thought....
Bob
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The only thing I question is the retention of the front O-ring on the valve piston.... You might be better to use a conventional poppet and seat arrangement at that point....
A valid concern, especially with higher pressures. With this configuration however there is no pressure to be put against the seat because the net pressure by definition needs to be pushing the piston away from the seat.
Here's how I imagine a balanced poppet could work, similar to how the cartridge designed by Michael Saxby (https://www.google.ca/patents/US4539969?dq=michael+saxby+cartridge&hl=en&sa=X&ved=0ahUKEwjM3M-Xnr7YAhUJziYKHXP3DkEQ6AEIMDAB) but with a much smaller pressure bias keeping the cartridge closed:
(https://i.imgur.com/rtY3MLB.gif)
Incidentally the Saxby & Palmer cartridge eventually manufactured did use an o-ring seal:
(https://i.imgur.com/XWtWuvd.jpg)
Another thought with more performance potential is the "valveless" design where the pellet itself seals the mouth of the cartridge, which would maximize flow and internal volume with zero "opening time":
(https://i.imgur.com/yZFaJSI.gif)
This does put a lot of stress on the projectile however which could deform and affect accuracy. Also crucially in practice were it to be made like this the friction from the balls pushing against the sleeve would make it impossible to move, increasing with pressure. It would be better to include a slightly unbalanced spool to compensate, although getting the proportions right would be a challenge. Too little bias and it will still be difficult to move, too much and it will fire as soon as it's pressurized.
(https://i.imgur.com/zSiCks8.gif)
The disadvantage of having a large diameter spool is that even though the diameters of the two ends might be identical, there is still a lot of friction that needs to be overcome and it increases with the diameter of the seals. The Inovairtech Magnum Air Cartridges for example uses a smaller diameter spool design, however this limits flow and dead volume:
(https://i.imgur.com/TwD7CPO.gif)
My ultimate aim for a cartridge airgun would be to generate enough pressure in the chamber to be able to cycle a semi-automatic action, and crucial to this would be a hammer that needs minimal pressure to actuate the cartridge. This is why the mechanically locked piston (https://i.imgur.com/XZyo5KK.gif) is appealing since the pressure moves the piston, thus negating the need for the hammer to overcome the friction.
The only other option that would have similar low hammer requirements would be an exhaust valve similar to the original subject of this thread, where a small diameter poppet empties a pilot chamber an the main chamber pressure moves a coaxial piston:
(https://i.imgur.com/lwcjecL.gif)
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Some mechanically locked designs I'm considering, drawn to scale:
(http://i.imgur.com/DMexznKl.png)
0.75" OD 3" long cartridge for a 3/8" (0.375") ball bearing projectile
(http://i.imgur.com/FFzJsHhl.png)
0.75" OD 3" long cartridge for a 3/8" (0.375") ball bearing projectile with spool piston to maximize internal volume
(http://i.imgur.com/Hj1zAL9l.png)
1" OD 4" long cartridge for a 0.875" shot load
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Cartridges are fine, but by definition are dump valves with limited volume.... That limits both the FPE and efficiency.... They have their place, providing your expectations are realistic....
Many very cool designs, BTW.... The one where the pellet is the valve may have problems with the skirt stretching as it passes the ball locks and into the barrel and rip the skirt off, or at least severely distort it....
Bob
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Cartridges are fine, but by definition are dump valves with limited volume.... That limits both the FPE and efficiency.... They have their place, providing your expectations are realistic...
I'm with you on the efficiency but don't you think some configurations would have the edge over hammer valves in terms of flow and opening time?
As you pointed out, using a lead pellet as the "valve" sounds good on paper but wouldn't really work in practice. I would think however that something like this with a sabot would get some good performance:
(https://i.imgur.com/ng6tNar.gif)
The dead volume is virtually zero as is the "opening time" if indeed there is any, there is full pressure on the base of the sabot the moment it starts down the barrel and the flow is equivalent to the bore without any asymmetrical turbulence. I'd wager you'd lose the sabot o-rings with every shot but it would probably be worth the performance.
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All dump valves have a pressure drop as the pellet moves down the barrel, in inverse proportion to the volume of the air you dump.... If you go larger than 50% of the barrel volume the gains in power are small compared to the amount of extra air ejected from the muzzle after Elvis has already left the building.... In fact, most guns using dump valves (eg. pumpers) have a valve volume of only 25-33% of the barrel volume for this reason....
Let's say your valve volume is 50% that of the barrel, and the valve is filled to 3000 psi.... You start with 3000 psi, and by the time the pellet is halfway to the muzzle you only have 1/2 x 3000 = 1500 psi, and when it gets to the muzzle, the pressure is down to 1/3 x 3000 = 1000 psi.... That means that 1/3 of the air in the dump valve is completely wasted each shot....
With a conventional timed PCP valve, and let's say a reservoir of 10 times the barrel volume (quite common), starting at 3000 psi, if you keep the valve open until the pellet reaches halfway to the muzzle (which releases the same amount of air as your dump valve contained), and close it at exactly that moment, the pressure profile would be 3000 psi at the start, 10/10.5 x 3000 = 2857 psi at valve close (compared to 1500 for the dump valve at half distance), and 2857/2 = 1429 psi at the muzzle (compared to 1000 for the dump valve)…. Obviously you will get more power from the higher pressure, and since you are using the same volume of HPA, you will greatly increase the efficiency compared to the dump valve....
In order to get similar power from a dump valve compared to a timed valve, you must dump more air.... If you dump 100% of the barrel volume, you will have 2000 psi at mid barrel and 1500 psi at the muzzle, still less average pressure than the timed valve, and now using twice the air.... and you are now blasting 50% of your air out the muzzle after Elvis has departed.... Double it again to 200% of the barrel volume, you will have 2/2.5 x 3000 = 2400 psi at mid barrel, and 2/3 x 3000 = 2000 psi at the muzzle.... This may get you close to the timed valve in power, but you are now using 4 times the air of the timed valve.... It is this combination of factors that drastically limits the balance of power and efficiency achieved by dump valves.... What the cartridge idea does have is a certain "cool factor", and of course the satisfaction that you managed to make it work....
You mentioned the "opening time", and whether that may gain you power, but consider this.... The wasted "transfer port volume" in a typical PCP is quite small, and calculations show that it fills so quickly that the pellet has barely begun to move by the time the pressure at its base is nearly reservoir pressure.... There is no real "flow volume" early in the valve cycle, only a sharp pressure rise at the base of the (nearly stationary) pellet.... The real "airflow" that occurs takes place late in the shot cycle, as the pellet velocity is higher.... Yes, there may be a slight advantage to having full pressure at the base of the pellet when it is released.... but nothing like the gains from the much higher barrel pressures available from a conventional PCP.... unless, as I showed above, you use a HUGE dump reservoir.... with the resulting horrible efficiency....
I don't have all the numbers in front of me, but one of the problems with the MAC cartridges is that the internal volume was insufficient compared to the barrel volume of the large calibers (eg. .357) they were trying to make work, and in addition the internal ports were too small.... barely OK for a .25 cal.... I can tell you that the internal volume was only 8 cc.... This severely handicapped the performance in the larger calibers.... They weren't even a decent performer in .257....
Bob
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Appreciate the detailed response.
With a conventional timed PCP valve, and let's say a reservoir of 10 times the barrel volume (quite common), starting at 3000 psi, if you keep the valve open until the pellet reaches halfway to the muzzle (which releases the same amount of air as your dump valve contained), and close it at exactly that moment, the pressure profile would be 3000 psi at the start, 10/10.5 x 3000 = 2857 psi at valve close (compared to 1500 for the dump valve at half distance), and 2857/2 = 1429 psi at the muzzle (compared to 1000 for the dump valve)…
I find it hard to imagine pressure behind the pellet equals chamber pressure before it starts to move, in fact being a dynamic system it seems dubious maximum barrel pressure would be anywhere close to the full chamber pressure. In practice this is what the barrel pressure vs projectile position curves would probably look like, assuming a "valveless" configuration for the dump valve setup:
(https://i.imgur.com/hNUwoY9.png)
As you say however while the peak pressure is lower, the average pressure would be higher for the timed valve resulting in greater acceleration and ultimately more power unless the dump valve chamber is unreasonably large.
I don't have all the numbers in front of me, but one of the problems with the MAC cartridges is that the internal volume was insufficient compared to the barrel volume of the large calibers (eg. .357) they were trying to make work, and in addition the internal ports were too small.... barely OK for a .25 cal.... I can tell you that the internal volume was only 8 cc.... This severely handicapped the performance in the larger calibers.... They weren't even a decent performer in .257....
Doubtless one of the reasons that Inovairtech seems to be in trouble as a commercial venture. Beyond the novelty factor of shell ejection, a cartridge system cannot compete with a conventional PCP in terms of ballistic performance and efficiency and that novelty factor will soon wear off when you're on the range being outperformed by fellow shooters with more traditional setups. As a platform therefore, a bolt-action rifle is likely the worst possible choice.
I'm after something a little more "fun", ideally self-loading firing a larger projectile (such as 3/8" bearings in a smoothbore barrel, with sufficient accuracy for plinking at short range) and sub 500 feet per second, that will probably look more like a movie prop:
(https://i.imgur.com/PuCTxQJ.png)
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I didn't say "before it starts to move", I said "barely begun to move".... Perhaps I should have said "before it moves very far".... Let's say the air molecules inside the valve are vibrating at a speed of 1650 fps, as they would be at room temperature.... When the valve cracks just a few thou (which is MUCH larger than the diameter of a molecule), some of those random movements are now past the seat, and the pressure in the exhaust port starts to increase.... The least time for them to reach the pellet base, for a 1" long port system, would be (1/12/1650) = 0.05 mSec (ie 50 uSec)…. Let's say it takes 4 times that long, or 0.2 mSec. before the pellet starts to move at all, and 0.5 mSec. for the pressure at the base of the pellet to rise to "almost" reservoir pressure.... The pellet starts from rest, and with 3000 psi pushing on it, in that 0.3 mSec. it will have only moved about 1/4-1/2" (for a typical example)…. light pellets a bit further, heavy bullets not as far, of course.... Certainly, not far enough to cause much of a pressure drop from it's movement along the bore.... and more importantly, in that brief time there will be little expansion of the HPA, and therefore little pressure drop, providing the reservoir is large (but a lot more drop for a small dump chamber)….
My point is that the pressure available at the base of the pellet is the most important thing in the acceleration process.... Yes, the first part of the acceleration is the most important, which is why high pressures are more efficient.... Your proposed model of the barrel pressures for a timed valve vs pellet position is not possible, or we could not achieve the performance we do with the short dwell time and high efficiency of typical PCPs.... Remember, many PCPs have the valve close before the pellet has even moved 20% of the barrel length, some 10% or less.... Here is a more likely representation of what is happening inside a PCP.... compliments of Lloyd's Internal PCP Ballistics spreadsheet....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/172%20cal%20Cedric_zpsrxcbwwwx.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/172%20cal%20Cedric_zpsrxcbwwwx.jpg.html)
While this is a representation of what happens with a small dump chamber.... I used a chamber volume of 1/2 the barrel volume, and had to increase the pressure to 3600 psi to get the same FPE.... even with zero "wasted transfer port volume" for the dump valve setup....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/172%20cal%20Cartridge_zps9icy5d0a.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/172%20cal%20Cartridge_zps9icy5d0a.jpg.html)
I'm not trying to convince you that you can't build a dump valve that will work and provide good performance, far from it.... I'm just trying to point out some of the pitfalls along the way to consider, and build around, in your design.... Some people won't care about the efficiency, figuring "air is free", and I can understand that.... Others, such as those hand pumping, will have a completely different attitude to keeping the valve open after Elvis has left the building.... ;)
Bob
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Thanks for that, I suppose I was visualizing it incorrectly - mainly not considering that the pressure rises behind the pellet at a much faster rate than one would think because of the limited volume and the relative speed at which the gas propagates.
Lloyd's Internal PCP Ballistics spreadsheet
Is this available for download?
I'm not trying to convince you that you can't build a dump valve that will work and provide good performance, far from it.... I'm just trying to point out some of the pitfalls along the way to consider, and build around, in your design.... Some people won't care about the efficiency, figuring "air is free", and I can understand that.... Others, such as those hand pumping, will have a completely different attitude to keeping the valve open after Elvis has left the building.... ;)
Just to add a bit of background, my experience in tinkering is mainly with dump valves. I've owned several PCPs throughout the years and did little in the way of optimization, keeping the commercially made airguns more or less separate from my other experiments. I have to say the past months looking further into hammer valves have been quite eye-opening and your data has been very helpful, I had definitely been harboring some misconceptions in this area. In this case though, efficiency is not a primary concern and indeed might prevent the blowback function I have in mind from working, there must be excess energy in order to eject the cartridge and give enough energy to the bolt to chamber a new round.
If you want to be horrified at the depths of inefficiency I have plunged to in the past, here's a design that just dumped a constant flow of air into the chamber, relying on a tight seal that the breech to act as a detent allowing pressure to build up in the cartridge:
(https://i.imgur.com/JzSZQ6K.gif)
I made an extremely primitive prototype (this was before I had a lathe and mill) to try out the concept and it worked pretty well:
https://youtu.be/cB1JzDdWlMc (https://youtu.be/cB1JzDdWlMc)
It took 850 psi to work however and with all that it could barely put a 0.177" BB through a soup tin, but at the end of the day I was more interested in the mechanism cycling that making something efficient.
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That is a really cool video.... and I certainly understand the joy of making an idea come to fruition.... 8)
Lloyd's spreadsheet is proprietary, and he has only given out a couple of copies of it.... I was one of the fortunate few, and of course cannot share it further.... Sorry....
I used to think there could be choking of the flow at both ends of the valve cycle, both opening and closing, when the poppet was close to the seat.... However once you realize that the airflow cannot exceed the pellet velocity.... and the molecular speed is much higher than that when the valve first opens.... it becomes obvious that choking of the flow, or indeed simple resistance to the flow, once the valve is open just a few thou, cannot be occurring on valve opening.... The delay is simply that of the random motion of the molecules becoming organized (from not bouncing off the poppet but passing through the gap between it and the seat)…. and a fraction of a mSec. before the barrel pressure reaches nearly the reservoir pressure.... during which time the pellet position has not changed much....
Bob
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Lloyd's spreadsheet is proprietary, and he has only given out a couple of copies of it.... I was one of the fortunate few, and of course cannot share it further.... Sorry....
That's fair enough, especially if it's part of his bread and butter.
I did however plug some numbers into GGDT (https://www.thehalls-in-bfe.com/GGDT/) and got similar results.
0.25" airgun with a chamber volume 10x the barrel volume at 3000 psi, firing a 31 grain pellet through an 18 inch barrel. I assumed valve opening time and transfer port volume to be zero, with the valve closing when the pellet is approximately half-way down the barrel.
(https://i.imgur.com/ENEi6DU.png)
With a chamber 0.5x the barrel volume and dump valve there is a 12% drop in muzzle energy:
(https://i.imgur.com/niyfekn.png)
In order to get the same energy, we either need to up the pressure by 22% to 3650 psi...:
(https://i.imgur.com/tjVNmCd.png)
... or increase the chamber volume by 130% to 1.15x the barrel volume:
(https://i.imgur.com/nfnOG8H.png)
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Interesting internal ballistics model.... I wonder why the barrel pressure at valve close is so low compared to Lloyd's?.... Perhaps because Lloyd calculates the pressure and then after that applies a correction (efficiency) factor, which takes into account things like the mass of air being accelerated.... whereas Hall applies those corrections before he plots the pressure curve?.... However, the results are similar, so it doesn't really matter.... ;)
Interesting to note that if you use 3650 psi, and the same 1/2 barrel volume, you are using 22% more "std. CI" of air.... and if you use 3000 psi but 1.15 barrel volumes, you are using 130% more air.... both to get the same FPE.... Pretty much as I would expect.... 8)
Bob
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Hall had made the point that GGDT goes a little funny at extremes, certainly the pressure curve looks a little odd for the timed valve, and when I added a bit of dead volume the FPE actually rose a little.
Here are some of the variables GGDT is supposed to take into account:
- Valve configuration and opening times. In fact, GGDT models four different types of valve: chamber sealing pilot, barrel sealing pilot, burst disc, and "generic." Each of these valves have different behaviors and GGDT accounts for these behaviors (more on that below).
- Pressure drop across the valve oriface.
- Temperature (and thus pressure) increase in the valve pilot due to work performed by gun gases on the valve piston/diaphragm.
- Gas leakage from the main valve body into the upper valve chamber (pilot).
- Performance differences due to different gases.
- Temperature effects on gas properties (and thus, performance).
- Performance limitations due to flow choking in the valve or the barrel.
- Valve effective oriface increases due to lowered valve throat Mach number.
- Temperature (and thus pressure) drop in the barrel due to work performed by the gas accelerating the projectile.
- Gas leakage around the projectile in the barrel.
- Compressibility (Mach) effects on air pressure both in front of and behind the projectile to include the creation of shocks.
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Yes, I saw that list, but of course it doesn't say how he accomplishes that.... Lloyd's spreadsheet also has a long list of "losses" that he allows for, some of which you can toggle on an off, with quite amusing "what if" results....
My guess is that some of the GGDT spreadsheet does not apply well to our very "small" caliber spud guns.... but then that is not what it was designed for.... In some of our highest powered PCPs, the air has more mass than the bullet.... :o
Bob
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My guess is that some of the GGDT spreadsheet does not apply well to our very "small" caliber spud guns.... but then that is not what it was designed for.... In some of our highest powered PCPs, the air has more mass than the bullet.... :o
No doubt, GGDT was written with a much more general scope.
I finally did some work today on this cartridge malarkey and it worked out pretty well!
Here is a youtube video with some testing, even without a barrel it packs a punch...
https://youtu.be/wb5Sf3Uzfhk (https://youtu.be/wb5Sf3Uzfhk)
Loud too, hearing protection was a must.
Here is the cartridge disassembled:
(https://i.imgur.com/ANWiyHR.jpg)
Everything held up well except the firing pin that took a beating and started to jam, it's the reason the piston can be seen to pop out in the last two clips in the youtube video. Needs to be made out of steel rather than brass.
(https://i.imgur.com/F6xGakf.jpg)
My crude fill rig consisting of a probe that is placed in the mouth of the cartridge with the assembly then being clamped in a vice for filling. It took 9 pumps from my cheap-o chinese pump to reach 1500 psi.
Filling and firing cycle animated exactly as built, scale is in centimeters:
(https://i.imgur.com/5sVlWwL.gif)
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Very Cool.... 8)
Bob
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Using steel rod for the valve stem will give you some more volume.
Looking good, interestin approach using ballbearings for locking the valve.
MAC cartridge was doomed from the start, they made a cool concept but the cartridge valve was very poorly designed, very inefficient, two small holes to feed the barrel, when it could have dumped like the Lane cardridge from the case mouth.
Marko
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Thanks guys.
interestin approach using ballbearings for locking the valve.
Not an original idea to be sure, almost all airsoft "40mm grenades" use this system. This example reverses the dynamic, with a central chamber and multiple "barrels" around it:
(https://i.imgur.com/7ZCr1qil.jpg)
The disadvantage of this configuration is that it lacks a balancing element so is only suitable for low pressures otherwise it is impossible to open.
Using steel rod for the valve stem will give you some more volume.
It can certainly be optimized, I'm thinking the piston made in two parts linked with a threaded rod. This is more of a proof-of-concept to answer some doubts that I had:
1) The effort needed to actuate the valve. The difference between spool seal diameters is 8.5mm vs 9.0mm, so the net pressure imbalance at 2000 psi is only 21 lbs, keeping the friction from the ball lock to a minimum and making it very easy to actuate. This should be well within the capabilities of a direct blowback mechanism.
2) Using a floating o-ring to fill the cartridge. This seems to work well, and it avoids the extra complication of installing a separate fill valve.
3) O-ring retention on firing. Having the front o-ring blow out with the flow was a concern but it did not happen at all during testing. My technique here to mitigate the potential issue is to cut a smaller o-ring groove and use a slightly undersized o-ring that is stretched in place.
MAC cartridge was doomed from the start, they made a cool concept but the cartridge valve was very poorly designed, very inefficient, two small holes to feed the barrel, when it could have dumped like the Lane cardridge from the case mouth.
I suppose it was a compromise in terms of ease of manufacture which is an important consideration for a unit that you have to make multiple examples of at relatively low cost. The spool is also relatively small diameter which reduces friction from the o-rings which means that you don't need a very strong firing pin, but it comes at the cost of air flow.
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Very Cool.... 8)
Bob
X2!
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Thanks!
Now that this has some chance of working I've progressed to the next stage of planning being what sort of blowback mechanism would be best.
(https://i.imgur.com/hzN6cfa.gif)
"closed bolt" mechanism with a separate spring-loaded firing pin.
(https://i.imgur.com/qk0e0FD.gif)
"open bolt" mechanism with a floating firing pin.
I'm inclined towards the latter, it's easier to build, perhaps less accurate due to greater movement before firing but that is not really a concern for what is meant to be a plinker. It will also cycle on full auto as long as the trigger is pressed, the closed bolt would be more difficult to implement as a select fire device. Not that with a limited amount of cartridges that would last very long anyway.
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Ive been lurking on this thread but just have to say how interesting this is! Very nice ideas. I actually considered the Innovairtech, but my inquires were never completely satisfied, mostly power issues. Have you evaluated these: http://air-ordnance.com/modoc-cartridge/ (http://air-ordnance.com/modoc-cartridge/) Not sure if its just a larger volume or actually different, mechanically. I wish they had a more traditional style rifle, I would get one. But maybe I need to wait and see what Jack comes up with and buy one of his ;)
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Thanks! I'm aware of the Modoc but have never seen a cartridge disassembled. Judging by what appears to be a substantial hammer, I would surmise that it is a simple spool system in the vein of the MAC or Brocock air cartridges. Apparently not a big success, from the the Airgun Academy article (https://www.pyramydair.com/blog/2015/11/the-modoc-big-bore-from-air-ordnance-part-1/):
The first Modoc had three air cartridges that all leaked. The second one had two bad ones and one that worked once. They even send a blank cartridge so you could fill the other two when one leaked. They knew that sealing was a problem.
Another shooter had a cartridge go off when the breech was open. The cartridge went into his abdomen and bruised him deeply.
So in my opinion, the Modoc is not safe. And it also doesn’t work very well.
It's a shame because it's a very attractive piece!
But maybe I need to wait and see what Jack comes up with and buy one of his
Oh this isn't a commercial venture, I'm just a very amateur machinist screwing around. That being said, if perfected the cartridges would not be difficult to put together with a limited number of CNC parts and in terms of a firing platform as mentioned before we have over a century of firearm design to be inspired by. The question is, what sort of platform would sell?
As Bob has repeatedly pointed out, such a design can never compete with a conventional PCP in terms of efficiency, so I don't see a cartridge design being a popular alternative for those who would like long range accuracy with a rifle that gives them as a many shots as possible for a given air volume.
I would see it more as a shotgun type platform, that makes the larger shells more "realistic" and I believe that a cartridge about the size of a 12 gauge magnum shell with an operating pressure of 4500 psi would easily yield more than 100 ft lbs at the muzzle. APS already make an airsoft shotgun sold for less than $400 (http://www.evike.com/products/47873/) so a similar platform slightly scaled up shouldn't be too pricey, in fact the idea seems to have been floated on this forum before (https://www.gatewaytoairguns.org/GTA/index.php?topic=89774.0).
Again, it would give you less power and efficiency than something like the Seneca Wing Shot (https://www.pyramydair.com/product/seneca-wing-shot-shotgun?m=3777), but it would be a 7 shot (or more with a tube extension) repeater, and what feels better than racking the pump?
Something roughly the external size of a .50AE pistol cartridge could yield around 20 ft lbs with a 0.22" pellet in a 8 inch barrel which would be good performance for a pistol sized package, thought I have my doubts that it would generate enough pressure in the barrel to operate a blowback mechanism.
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I was only half joking when I said I should wait, I realize you are brainstorming here. However, there are multiple reasons reasons for product development and your intentions alone are worthy. It would be great if all new R&D had more efficiency, longer life cycle, improved performance, sustainable manufacturing, sustainable life cycle, sustainable repurpose, less expensive, etc. Even if it was less efficient fpe/ci, and I could fill cartridges to carry instead of a bottle....................Wingshot for instance (actually I was considering the PBBA 20) filling after 2-3 shots was not appealing to me.
Thanks for feedback on the Modoc, I had also heard some leaking issues. Funny, I had just run across a video from Lethal Air about APS, and I think they said they were coming out with a PCP. I then did a search and found them, pretty darn cool! I also came across a couple of videos from a guy I had seen in the past, Markhobby..............he was filling those cartridges to 2000psi Ive never been into airsoft but seems pretty interesting and brought me back to your thread. Pretty interesting................
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I like the air cartridge concept, mac had a good idea but bad design. Would be interesting to see how it would perform with a different valve arrangement.
For plinking fun it should be sufficient, with powder burner type action and realism.
Shooting big cased ammo without the noise and miles of safety area behind your target.
Marko
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For plinking fun it should be sufficient, with powder burner type action and realism.
Shooting big cased ammo without the noise and miles of safety area behind your target.
Marko
That’s what I’m thinking, which is generally what got me into air.
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Shooting big cased ammo without the noise and miles of safety area behind your target.
Regarding the noise, this one's pretty loud, I certainly would not fire it without hearing protection. Hopefully when fired within a breech and barrel that will allow room for the gasses to expand before exiting to the atmosphere it will be more tolerable.
Speaking of airsoft, here is the APS APM cartridge for the APM50 rifle (http://www.aps-concept.com/index.php?route=product/product&path=20_84&product_id=81):
(https://i.imgur.com/8ExoK5f.gif)
Note that this is the "Angel" low power version, which is why the air chamber is so small relative to the cartridge body. The firing and filling cycles are shown.
You can see that the concept is virtually identical to the MAC cartridges, indeed it might have been the inspiration as it predates Inovairtech's products.
(https://i.imgur.com/iU29iq3.jpg)
I've been thinking about simplifying the design in the interest of easier manufacture, since I'll be wanting to make a few of these.
Here is my current thought, with one o-ring at each end simultaneously sealing the piston and the chamber, sandwiched with Delrin washers pushed by a single spring:
(https://i.imgur.com/p0PDoqT.png)
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Some other pressure-driven design variations presented for the record:
(https://i.imgur.com/skOnXza.gif)
Balanced spool where the firing pin exposes a stepped piston that blows the assembly back to dump the cartridge
(https://i.imgur.com/Jmc8FeM.gif)
Variation of the above where the rear seal is a poppet type and the piston is blown forward
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Now that I'm scratched the hammer valve itch I think I'll get back to this, I have an airsoft 1911 frame lying around that I think will make a good basis for a shot pistol, initially single shot but with the option to make a side-loading magazine.
Here's a quick scale drawing of what it would look like using a 1" OD 0.825" bore cartridge:
(https://i.imgur.com/WetIFWq.png)
The green bolt would have a flat milled on its left side to allow it to travel past an ejector that would swing the cartridge out towards the right side on firing.
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Nothing new under the sun is there, here is a patent for an exhaust valve air cartridge (https://patentimages.storage.googleapis.com/d5/df/19/6e73dfbe1f1be5/US387256.pdf) with a spool piston from 1888:
(https://i.imgur.com/ZJINYSn.png)
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Here's an idea I had for a 12 gauge sized cartridge for the purposes of amusing oneself with powderburners where excess noise and damage would not be tolerated:
(https://i.imgur.com/yAnyO07.gif)
The sabot seals a balanced port while the cartridge is at rest. On firing, the pin moves a balanced spool that unbalances the sabot, causing it to fire. I made a prototype and it worked:
(https://i.imgur.com/9F0C7gc.jpg)
(https://i.imgur.com/lM0Pe7U.jpg)
(https://i.imgur.com/4WDyV4r.jpg)
I found it to be a little fragile though, the slightest leak from the spool could cause it to fire unexpectedly so not the safest of concepts.
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According to the following video AEA is bring this (or something like it) back:
https://youtu.be/2_VhQZAjMaQ?t=313
Also mentioned in the same text is .50 BMG.
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Sorry, but any company that operates only on Facebook or YouTube, without an actual website, does not interest me in the least.... I consider it to be Vapourware until they are actually available and tested by GTA members....
Bob
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It was mentioned in this thread (https://www.gatewaytoairguns.org/GTA/index.php?topic=159669.0) but it seems to have been more of an aspiration than an actual prototype that had been put together.
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If wonder if the delay has to do with them being very careful about which models to import first?
Air cartridge models vs. bottle fed models?
The following AEA prototype demonstrated in June uses the .50 BMG air cartridge. (.016 liter internal volume) and looks rather attractive and versatile to me:
https://www.facebook.com/TheSlingshotChannel/videos/651479891996598/ (https://www.facebook.com/TheSlingshotChannel/videos/651479891996598/)
(Shoots 2200+ grain hollow arrows or slugs)
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Another AEA air rifle called the "Monster" that uses Jumbo Air cartridges:
https://youtu.be/Fvl4puyJHHs?t=282
Claimed power for each 2200+ grain arrow shot is 600 Joules (442 FPE).
P.S. Power does seem a bit low for such a large cartridge at 5000 psi.
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Sorry, but any company that operates only on Facebook or YouTube, without an actual website, does not interest me in the least.... I consider it to be Vapourware until they are actually available and tested by GTA members....
Bob
My sentiments exactly regarding all things, not just AGs and AG related stuff. And I don't/won't do ZuckBook, period. ZuckBook is pure evil.
Google/Youtube is also evil, but at least for now, I have no choice except that I use duckduckgo for searches.
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Another AEA air rifle called the "Monster" that uses Jumbo Air cartridges
That is very impressive, probably not on the efficiency front but I think you'd be able to argue that in practice you probably only need one shot...
That being said, the "cartridge" isn't exactly compact, looks to be about the size of a 37mm anti-tank gun round!
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Another AEA air rifle called the "Monster" that uses Jumbo Air cartridges
That is very impressive, probably not on the efficiency front but I think you'd be able to argue that in practice you probably only need one shot...
That being said, the "cartridge" isn't exactly compact, looks to be about the size of a 37mm anti-tank gun round!
Agree the efficiency would not be good if using a .357 barrel like the AEA Harpoon.
Maybe in addition to that arrow (which is also shared with the .50 BMG cartridge using harpoon) they have some large caliber slug barrels planned as well? (Example: 16" .72 barrel is only ~ 107cc).
I wonder how much internal volume that Jumbo air cartridge has? The diameter looks to be the same as the 16cc .50 BMG but the body is longer.
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After putting it aside for a while, I've made a little more progress on this concept in the form of an air cartridge designed to fit a 26.5mm flare gun to turn it into a flair gun ::) ;D
With the previous design it was not handling higher pressures well, with the aluminum piston being deformed by impacts at the end of its travel, and the fact that the locking balls moved with the piston causing their own issues with wear and jamming. I therefore altered the configuration, now the balls are on a fixed stem, and the piston is made of steel. Here is an animation approximately to scale, not shown is the piston return spring and an o-ring around the stem that acts as a shock absorber:
(https://i.imgur.com/fMDm079.gif)
I've only done some preliminary testing with air only for the time being as it's still barrel-less, but even that is quite promising (and incredibly loud, hearing protection is a must!) and here is a test shot at 2500 psi to the detriment of a plastic cup that was literally blown to smithereens:
https://youtu.be/8jp6Ljt730Y
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Welcome back, Jack
Very impressive design and blast.
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excellent work jack , pretty cool. did you make the gun for this , or is this a repurposed flare gun?
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Thanks gents!
did you make the gun for this , or is this a repurposed flare gun?
The latter, it's a former Soviet SPSh-44 (https://en.wikipedia.org/wiki/SPSh-44) flare gun that hasn't been modified.
Looking forward to seeing what can be done with all that pressure and a fast valve, I'm thinking 0.75" smoothbore slugs ;D
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Cool stuff!!
Dave
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Very nice!
Should be fun to make one for the 12 gauge.
Need to think about it.
Marko
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Should be fun to make one for the 12 gauge.
Something similar is definitely on my list, I think it can be scaled down to fit a 12 gauge sized cartridge.
I made a 60mm long barrel in the meantime and had a little fun using empty 12 gram CO2 cartridges as projectiles:
https://youtu.be/cK2CSSHOnbw
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thats some serious power in a compact frame !!!!!!!!!!!!!! holy cow.. not sure what an empty 12 gram co2 weighs , but im guessing 300 grains
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Is that FPS? I am impressed that it is piecing the can, and not just pushing it away.
How many FPE?
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not sure what an empty 12 gram co2 weighs , but im guessing 300 grains
15 grams so 230 grains
Is that FPS?
Yes, that works out around 23 ft lbs
I am impressed that it is piecing the can, and not just pushing it away.
It's fairly marginal, in one of the shots you can see that the projectile started to tumble and hit side-on and it didn't actually pierce the can.
I'm sure it can be optimized for more though, for example I think the piston bumper is limiting valve opening somewhat.
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Cool level....
(https://miro.medium.com/max/490/1*pQbNlbeSzdSWSj8s3a3S_w.jpeg)
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what AL said , I want one ;D
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Have to agree, that’s just too cool!
Dave
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I confirm it is indeed very cool ;D
So it turns out there was something very wrong with the balance I was using, an empty CO2 capsule averages at around 30 grams, not 15 grams, so muzzle energy for those first tests was actually more in the 45 ft lbs range :o
In the interest of ramping things up further, I "made" a better projectile by cutting down a 12g capsule to an inch in length, now weighing in at 10 grams:
(https://i.imgur.com/mfOwqwI.jpg)
At 3000 psi I got 441 fps:
https://youtu.be/IeIHCMiqoG8
That works out at 67 ft lbs, not too shabby for an air pistol :D
Normally heavier projectiles tend to generate more energy in pneumatics, but for a 20% increase in pressure I got a 55% increase in muzzle energy, with a lighter projectile.
I would surmise that one of the factors is the fact that the "cup" shape of the cut down capsule makes better use of the airflow.
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I wonder what it's like with an actual barrel. Is the plan to use it like a breech loader or some kind of repeater?
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thats incredible , such a compact gun , granted its 19mm bore lol
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Oh yeah, I just hafto make one of those!
Marko
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Jack, you are Newton's fourth law of motion: Objects in set in motion by Jack are going to cause spectacular damage. :)
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I wonder what it's like with an actual barrel. Is the plan to use it like a breech loader or some kind of repeater?
I first dreamt of this sort of mechanism in my adolescence because basically my access to firearms was not commensurate to my access to them, that's changed considerably in recent years so the impetus to make something to fire these from scratch is somewhat faded. I'm more inclined right now to make a more compact iteration that will fit in a 12 gauge shotgun.
Objects in set in motion by Jack are going to cause spectacular damage. :)
While many airgunners focus on accuracy (and rightly so) I must admit to being a little more power mad ;D
In the spirit of showcasing a bit more mayhem I've created a separate thread (https://www.gatewaytoairguns.org/GTA/index.php?topic=205498.0) with more details of this particular project.
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Only one thing to say....
WOOF! ;D ;D ;D
Awesome! 8) 8) 8)
Jesse
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(https://i.imgur.com/PCpCGJR.png)
Some design thoughts for a 12 gauge air cartridge, the ball lock mechanism takes up a lot of chamber space so I'm wondering if an exhaust valve would be a better idea, filled through the rear with the pilot valve doubling as a check valve.
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i assume the rear piston diameter is either smaller or same diameter as the front poppet in the last iteration
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Having still been working with pilot activated valves, I’ll throw out a couple things.
No orings are needed in the design, it will work just fine without. I think from a safety standpoint, eliminating the orings would keep the main poppet from blowing open in the event of a slow leak at the pilot poppet. It would also allow slow filling from the pilot end.
The other suggestion is to keep the pilot very small. The leshiy 2 uses a very small ceramic ball for example. I use approximately a .090” throated pilot and it’s plenty.
I look forward to you trying one.
Dave
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i assume the rear piston diameter is either smaller or same diameter as the front poppet in the last iteration
It's slightly larger, it cannot be smaller than the poppet otherwise even with the pilot volume empty it will never open. The piston needs to be biased towards the rear when the pilot is empty.
Here is a quick animation of the cycle:
(https://i.imgur.com/oQhRCdV.gif)
Thanks for the tips Dave, while not having dabbled much beyond 850 psi I have quite a bit of experience with exhaust valves, one of my very first home made pneumatics over two decades ago was a very primitive iteration of this mechanism:
(https://i.imgur.com/61LTOpJ.jpg)
No orings are needed in the design, it will work just fine without. I think from a safety standpoint, eliminating the orings would keep the main poppet from blowing open in the event of a slow leak at the pilot poppet. It would also allow slow filling from the pilot end.
This is a good point, a tight fit should also work as long as there is good flow from the pilot valve and the pilot chamber volume is limited.
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makes sense Jack , so long as theres enough balance to keep the poppet closed while filling .