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Originally Posted By: Rocketman
The red "ink" is for keeping direct responses separate from the original text. No meaning attached to the color. If this technique is offensive to you, say so and I'll not use it any more.

So are we to believe that just because the wad skirt of a 28 ga. wad can be flared out to .729" or so, it will still contain perhaps 9000 p.s.i. without that skirt blowing forward and losing its' perfect seal? Maybe not 9,000 psi. But the pressure has dropped considerably by the time the wad base must expand to bore diameter. That would be some tough skirt. Yes, the plastic in wads is very tough. Whew! I will still contend that even if that wad could contain the pressure, as the area almost instantly increased, the pressure would have to drop and force would remain equal (assuming zero blow by). I agree that this is very close to what must happen. Anything else would absolutely be claiming a physical free lunch. The only issue would be if the larger bore turned out to be a bit more efficient for the powder to burn/expand into. This could account for a small increase in wad base force and velocity. Are you saying that if we have, for example, 9000 p.s.i. gas pressure contained in a one cubic inch cylinder and we increase the volume of the cylinder to two cubic inches, that we would still have 9000 p.s.i.? Certainly not... not without adding more gas or superheating the same gas in the doubled volume. Now, I wish I knew how to put your following statement in red letters (highlite the text you wish to color, click on the "A" with a color bar under it in the bar above, and click on the color you wish) : "If the wad base expands to fill the larger bore, then, yes, the force increases. This is how a small hydraulic piston raises a large load on a bigger bore cylinder." Whiskey Tango Foxtrot. No, no, no. Huh uh. Nope. In a hydraulic pump, be it a simple hand Porta Power type pump (or a simple hydraulic jack), or a multi stage variable displacement rotary piston pump, the small diameter pump piston(s) driven by hand or motorized force displace a volume of relatively incompressable (or it could be a compressible gas) oil equal to the bore radius squared times pi times the stroke (length). This volume of incompressable fluid under pressure acts upon the base of the larger cylinder piston and moves it a porportionately shorter stroke. The larger the cylinder piston, the less one stroke of the pump piston will move it. Again, there are no free lunches here. Suppose we wish to lift 1000# with a cylinder having 10 sq in area. We will need 100 psi on the base of the cylinder (10 sq in X 100 psi = 1000 lbf). Suppose we have a pump piston with 1 sq in face area. Then we will need to apply just over 100# force to the piston to cause the fluid to flow to the cylinder and displace it. If we are unable to supply 100# force to the piston (1 in X 100 lbf = 100 psi), no fluid will move (the pump will stall). Pressure is constant within a hydraulic loop, but force is not at all constant. Your example is a fine statement of the displacement principle (second step), but assumes the pump has sufficient pressure to move the fluid. I working a step back where we have to know the pressure to force balance and area (first step). If the pump can't supply sufficient pressure, it will stall and no fluid will move. You have to work both steps. Lifting 1000# with 100# force seems like a free lunch. You pay for lunch with the displacement - sorta like spreading the payment out.
Rocketman, Having read perhaps hundreds of your posts, I knew that you knew better than you originally stated, the working principles of hydraulic pumps. However, if our pump/cylinder system was using a compressible gas instead of an incompressible oil, I don't think it would be considered a "hydraulic" system. Also, my example did not state the obvious that if the pump did not produce sufficient pressure, it will stall and no fluid would move. I also did not state the equally obvious that if our hand pump operator had no arms and could not pump the pump that no fluid would move either. My mistake. I do agree that something may happen to make the powder burn more efficiently as it expands into the almost instantly larger combustion chamber. Earlier in this thread, I postulated that we might even be seeing a sort of the phenomena that occurs with reduced loads of some powders that produces pressure spikes or even detonation. See the cautions and warnings about reduced loads of WW 296 in the .357 magnum for example. That is why I wish we could simplify this discussion and power our wad/shot charge with say 9000 psi of compressed air or CO2. Then we could say with certainty that the pressure would have dropped considerably by the time the wad entered the larger bore diameter. With some slower powders, that may not be true. In any case, despite the toughness of the wad skirt, I am still very skeptical that there would be no blow by going from 28 ga. to 12 ga., or .550" to .729" (I don't know the diameter of an average 28 ga. wad.) I do know that in hydraulics or pneumatics, even where the bore size does not open at all, let alone so dramatically, there is no such thing as a perfect seal. Why, with what you are claiming, we all should be loading our 12 ga. shells with 28 ga. wads. We would get higher velocity at lower pressure with reduced bore friction. I suppose we could put up several thousand dollars and have some ballistics lab prove that you or I are right or wrong. But I think I'll just save my money for my daughters' college tuition and to buy more shotguns. Oh, your use of red text is in no way offensive to me. I'm not easily offended. That's why I would never consider using the "Ignore" feature here. Meanwhile I'll leave you with a cool quote from Aristotle that may apply to you and me: "The world is divided into people who think they are right." As I did not confirm this, I expect you or someone will correct me and say that Socrates or Plato said this.

Last edited by keith; 10/22/09 01:46 AM.

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It must be understood here that simply dropping a smaller wad into the larger shell is not the same as firing a smaller shell in an adapter. The wad "Fits" the smaller shell & has its pressure up before exiting the end of the case so it immediately expands. Just drop that smaller wad into the larger hull & seat it & you will have powder outside the wad to begin with. Touch her off & you are obviously going to get immediate blow-by & the wad will most likely never obturate efficently at all.
"Totally" different circumstances.


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Rocketman, Having read perhaps hundreds of your posts, I knew that you knew better than you originally stated, the working principles of hydraulic pumps. However, if our pump/cylinder system was using a compressible gas instead of an incompressible oil, I don't think it would be considered a "hydraulic" system. The foundation pirincples of force equals area times pressure applies to all fluid systems. Also, my example did not state the obvious that if the pump did not produce sufficient pressure, it will stall and no fluid would move. I also did not state the equally obvious that if our hand pump operator had no arms and could not pump the pump that no fluid would move either. My mistake. I know you understand, but others reading this discussion may not have. Public discussions, such as this, have to provide more background information than a simple two-way discussion. I do agree that something may happen to make the powder burn more efficiently as it expands into the almost instantly larger combustion chamber. Earlier in this thread, I postulated that we might even be seeing a sort of the phenomena that occurs with reduced loads of some powders that produces pressure spikes or even detonation. See the cautions and warnings about reduced loads of WW 296 in the .357 magnum for example. I'm not aware of any detonation issues with shotguns; sure for rifle and pistol low density loads. However, the detonation phenom occurs within the case. That is why I wish we could simplify this discussion and power our wad/shot charge with say 9000 psi of compressed air or CO2. Then we could say with certainty that the pressure would have dropped considerably by the time the wad entered the larger bore diameter. With some slower powders, that may not be true. In any case, despite the toughness of the wad skirt, I am still very skeptical that there would be no blow by going from 28 ga. to 12 ga., or .550" to .729" (I don't know the diameter of an average 28 ga. wad.) I do know that in hydraulics or pneumatics, even where the bore size does not open at all, let alone so dramatically, there is no such thing as a perfect seal. Agreed, but the wad skirt seems to be able to bloom the noted 0.09" in radius and maintain a seal. Why, with what you are claiming, we all should be loading our 12 ga. shells with 28 ga. wads. We would get higher velocity at lower pressure with reduced bore friction. No, I don't agree with that statement. 28 gauge shells may actually preform better in a 12 gauge bore, though. I suppose we could put up several thousand dollars and have some ballistics lab prove that you or I are right or wrong. I not interested in who is right or wrong. I'm interested in what is true. [/quote]

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Rocketman (and Miller), my statement that perhaps we should all be loading our 12 ga. hulls with 28 ga. wads was, of course, facetious. I had hoped that was self evident. I am also aware that Guagemates "work", but I am skeptical that their use can impart any magical miraculous qualities to a load that defy physics. I expect that a wad skirt blooming out .09" would still contain a lot of the gasses behind it... I just doubt that seal would be anything near perfect. I have seen too many materials from simple leather cups to steel rings to exotic polymers, running in near perfect bores, without the piston running in a bore that suddenly opens .179" in diameter, and know that they all leak (if only a miniscule amount). Perfection would give us the exact same force. Anything less would be a loss, however slight. Any thing more would be impossible, save for some gain from more efficient powder burning in the larger bore as you theorized, or the pressure spikes or detonation I theorized. But I roll my eyes when some speak of magical 13% gains. Like you, I am not aware of detonation issues with shotguns, for sure. I am aware of unexplained shotgun ruptures. They may be due to unknown bore obstructions, dents or barrel defects, or who knows. I know that a friend claimed that it was much reduced loads that blew up his brothers' Beretta O/U back when we were in high school. But I can't prove he was telling the truth as I only saw the aftermath. This friend did play with reduced loads, but he also made up loads that would have left Roy Weatherby shaking in a cold sweat. All I know for certain is that big brother was pissed. Big time pissed. Finally, like you, I too am interested in what is true. I said as much a couple pages back and also said much of this discussion is conjecture. Now conjecture based upon education and years of practical experience beats wild assed guessing and data from the U.S. Journal of Wildly Innacurate Information (a source I may have used to complete one or two late night, last minute term papers). But it is, without extensive unbiased testing, still conjecture. What that means ultimately, I hope, is that we can have these lively and thought provoking discussions, much like those my buddies and I have at the Camp (sometimes fueled by beer and bourbon)... and in the end, remain friends.

Last edited by keith; 10/23/09 11:43 PM.

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Originally Posted By: keith
Rocketman (and Miller), my statement that perhaps we should all be loading our 12 ga. hulls with 28 ga. wads was, of course, facetious. I had hoped that was self evident. To me, it was, but, likely, not to all who are reading this discussion. I am also aware that Guagemates "work", but I am skeptical that their use can impart any magical miraculous qualities to a load that defy physics. I expect that a wad skirt blooming out .09" would still contain a lot of the gasses behind it... I just doubt that seal would be anything near perfect. I wouldn't expect a perfect seal, but one that was "good enough." I have seen too many materials from simple leather cups to steel rings to exotic polymers, running in near perfect bores, without the piston running in a bore that suddenly opens .179" in diameter, and know that they all leak (if only a miniscule amount). One pass through a bore is different from multiple passes. I have no doubt that all shotgun wads leak far more than could be tolerated in a multiple pass system. Perfection would give us the exact same force. Don't agree with this statement. A perfect seal would only mean we had all the gas contained and the highest possible pressure possible within the system of shell, Gauge Mate, and gun barrel. We would not know how the wad base force was affected without knowing the pressure after expansion into the barrel. If the loss of pressure due to expansion and leakage turned out to be less than the gain in wad base area, we would see higher velocity. If the loss of pressure netted more than the gain in wad base area, we would see reduced velocity. Remember, forec is pressure times area. We know the new area, but not the new pressure. Anything less would be a loss, however slight. Yes, but a slight loss in pressure due to a small wad leak does not automatically translate into lower velocity. It is entirely possible that the increase in wad base area more than compensates for the loss of pressure due to both expansion and to leakage. Any thing more would be impossible, save for some gain from more efficient powder burning in the larger bore as you theorized, or the pressure spikes or detonation I theorized. Or, the force is higher due to the net of the expanded wad base area times reduce pressure still being higher. But I roll my eyes when some speak of magical 13% gains. Like you, I am not aware of detonation issues with shotguns, for sure. I am very sure that pressure spikes and detonation do not factor into this issue. A spike or detonation would for sure reduce the efficiency of the system and, if contained, result in lower velocity. I am aware of unexplained shotgun ruptures. They may be due to unknown bore obstructions, dents or barrel defects, or who knows. I know that a friend claimed that it was much reduced loads that blew up his brothers' Beretta O/U back when we were in high school. But I can't prove he was telling the truth as I only saw the aftermath. This friend did play with reduced loads, but he also made up loads that would have left Roy Weatherby shaking in a cold sweat. All I know for certain is that big brother was pissed. Big time pissed. Finally, like you, I too am interested in what is true. I said as much a couple pages back and also said much of this discussion is conjecture. Now conjecture based upon education and years of practical experience beats wild assed guessing and data from the U.S. Journal of Wildly Innacurate Information (a source I may have used to complete one or two late night, last minute term papers). But it is, without extensive unbiased testing, still conjecture. What that means ultimately, I hope, is that we can have these lively and thought provoking discussions, much like those my buddies and I have at the Camp (sometimes fueled by beer and bourbon)... and in the end, remain friends. For sure we remain friends. It must be possible for friends to debate issues without getting personally angry. I much enjoy lively debate that challenges what I think I know and makes me consider new angles or information. Thanks for the discussion. Keep it coming!!

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Very interesting thread for this "city boy" who barely got out of High School. "Higher" education came from the School of Hard Knocks and extensive reading and practice.
I don't pretend to understand the velocity "WHY", but I can report the increased velocity WHAT when I used ChamberMate (not Gauge Mate) brand chamber inserts.
I took five of my personal 12GA shotguns, all with 30" barrels, and identified them by their bore diameter - 741" Gun, .731" Gun, .729" Gun, .727" Gun, and .725" Gun. Newly bought Winchester brand ammunition was used in 12GA-20-28-410. Five 12GA rounds were fired in each 12GA gun to establish my benchmark velocity average in 12GA in each gun. Then I repeated the tests with the ChamberMate inserts in 20ga, 28Ga and 410 in each host gun. All rounds fired over my chronograph and recorded.
Rocketman mentioned he did not think resistance (barrel roughness?)would have any affect....firing results from my .727" Gun would seem to challenge that idea, as it showed a consistently lower average velocity in all gauges fired therein.
I just could not understand how I ended up with a "velocity increase" for each sub-gauge. A Dixie gent whom I greatly respect and had the benefit of a Clemson education, said I should file the results under "gas expansion dynamics".
I wrote up my results in a "rough&ready" report for my files and reference. Anyone interested in this "report" e-mail me and I'll send it along for your perusal.

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Ian, I certainly "buy" that a rough bore might leak more gas than a smooth bore, resulting in lower velocity. Could be, also, that there would be a more macro friction than I was thinking of in the previous statement. I'm always glad to see data from you and to factor it into my thinking. Theory is fine, actually very handy when we have nothing else or need to explain what we have. I'd love to see your real data (don.amos@conti-na.com). BTW, I, for one, don't care where your formal education stopped. I know for sure that you turned your life experience into a fine and useful education.

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