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You totally misunderstood my post, Miller. I'm in 100% agreement with you about this, and have been for as long as I can remember. I copied and pasted an old post of yours from '16, concerning setback damage to shot, and the reply from a poster that goes by "cpa", who didn't believe the bottom shot in the payload are "squashed" more than those further towards the front.

Sorry if I wasn't clear. We're on the same page. He isn't.

SRH


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Since you brought up the old post, just to make things clear I didn't say the bottom shot were more, or less, squashed. The discussion began, I believe, with the assertion that a 1 oz load in a 28 gauge required more force to achieve a certain velocity than a 1 oz load in a 12 gauge. That is simply not the case although force per square inch would be greater in the 28 gauge. Then it was asserted that the shape of the mass (long column of lesser diameter in the 28 ga.) would determine the inertia of the shot charge - again, don't think that is correct.
I questioned the acceptance of common knowledge, beliefs and anecdotal evidence as "proof" of the statements about deformation. Wonko the Sane also questioned that, but more forcefully than did I.
If you read my final comment, it should be clear that I stated that there was a lot going on as the shot charge moved down the barrel, that it was complex and that probably much was not known.
For example, have you thought about the relative impact on the lower level of shot as the upper level is slowed going through the forcing cone and the choke and how any resulting deformation might compare to the initial explosion deformation? It would be interesting to make a barrel without a forcing cone and choke so that the shell case would fit the chamber more like a rifle and the shot charge could enter the barrel unimpeded. Or make a shell case with the shot charge in an enclosed plastic container that actually fit the barrel similar to the Speer handgun shot containers.

Last edited by cpa; 06/16/19 10:30 PM.
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Quote:
It would be interesting to make a barrel without a forcing cone and choke so that the shell case would fit the chamber more like a rifle and the shot charge could enter the barrel unimpeded.


They did that, called it a Chamberless gun, they did though normally have a choke.
M/Lers had no forcing cone & most were cylinder bore. They, of course, did not use a case. They both shot extremely well.

Bore area is proportional to the Square of their diameters, therefore the 12 ga bore has about 40% more area than the 20 & about 75% more than a 28. If you fire for instance an ounce of shot out of each @ 1200 fps, you have indeed applied the same amount of Work. The Pressure to move the load to that level will though be 75% more for the 28 & 40% more for the 20 than for the 12, all figures in PSI or pounds per square inch. PSI is what deforms the shot, NOT total work.

Note also this pressure is NOT meaning the peak pressure but the total pressure applied. Even if by use of a slower burn powder we bring the Peak pressure of the smaller gauge down to a similar level to the 12, that pressure will be maintained for a longer period of time.

"IF" we were talking Static pressure then the applied time would be meaningless, but for the milleseconds involved here it does in fact become meaningful.


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Originally Posted By: cpa
For example, have you thought about the relative impact on the lower level of shot as the upper level is slowed going through the forcing cone and the choke and how any resulting deformation might compare to the initial explosion deformation?


It isn't slowed at all. The shot charge acts as a fluid in motion and is speeded up due to the venturi effect when passing through a constricting area, such as a choke. And, that is not "common knowledge, belief or anecdotal evidence", it is scientific fact. Thus, there is no further significant deformation, due to setback, after the initial ignition and movement from static.

SRH


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Stan;
Can you cite the data that proves that as "Scientific Fact"? There is data extant that tends to disagree with that Fact.


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You know, Miller. I think I spoke too hastily in using the term "scientific fact". I have read Rocketman relate it so many times over the last 13 years on here, that I had come to accept that it is scientific fact. I cannot prove it with data, but when he explains it, with his lifetime engineering background, it makes so much sense that I accept it, too.

My apology to cpa and to the board for calling something fact that I cannot back up with data. That data may well exist, but I cannot put my hands on it.

Just for funsies, type "venturi" into the search engine on this forum and read all the times Don (Rocketman) has explained the principle, and how it applies. BTW, thanks for holding my feet to the fire on it.

Would you, in turn, please cite the data that disagrees with my (and Don's) belief of how a shot charge acts when encountering a forcing cone or choke cone (venturi)? I would seriously like to read it. Thanks in advance.

SRH


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Stan;
The data I have was cited by Burrard. unfortunately, when I was entering chemo back in Oct of '17 we had to do some re-arranging of the house. Somewhere, Somehow my copy was misplaced & has not been found yet. I Fear the Worst, that somehow it got in the trash. "The Absolute Best Book" I have ever had on shotguns.

I will do the best I can from memory. A heavy pendulum gun was made up with as I recall a 24" barrel. This barrel was fitted with a crusher pressure sensor. Barrel extensions were made up to around 32" as I recall with each one very carefully fit to within a couple of Ten Thousandths of an inch (.0002") & carefully lapped in for no step in the bore. The two of interest for this discussion though were two 30" total lengths with one Cylinder bore & one Full choked. Loads were loaded using several powders all in the nominal 2˝" chambering & with the nominal British Game load & Velocities were recorded at the customarily observed vel over 20 yards & the recoil recorded. Interesting thing was that within each barrel recoil varied according to the velocity of each individual load as would be expected.

What was Not expected was that while the observed velocity was slightly higher for the Full barrel than for the Cyl barrel, the Recoil Reversed with the Cylinder barrel showing a very slight but consistent increase in recoil. So far the only explanation for this was the cylinder barrel was giving a very slightly higher velocity than the Full barrel. What could account for this other than a slight checking of the shot upon hitting the choke?

Nota Bene (Note Well) I consider Don to be one of the very most knowledgeable posters we have here & I have learned a tremendous amount from him over the years. Never-The-Less I am not thoroughly convinced that solid shot behaves identically to a liquid or gas in passing through that venturi.

Also in the early days of choke boring, many barrels had very thin muzzle walls. Problems were soon encountered with bulges at the choke or as the Brits called it Lifting the Choke. This would tend to indicate a slight checking of the charge & the creation of an obstruction shock. Most did not bulge but simply had a slight ring bulge at about the beginning of the choke.

If anyone has any data as to what is the absolute closest to the muzzle it has been possible to record velocities I would like to have this knowledge. The difference in absolute muzzle velocity & that at even 2 or 3 feet is easily accounted for by the speed at which the shot from the cylinder bore disperse & drag affects the individual pellets rather than the whole charge reacting more like a solid projectile from the choked barrel. All I've got at the present.

Sure Wish I could find that "The Modern Shotgun" book. The Most Valuable book I have ever owned in my entire life is "The Holy Bible" but this was the most valuable one I ever had relating to shotguns, & not just from a monetary sense but the value of the information therein.

Last edited by 2-piper; 06/17/19 10:09 PM.

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Thanks, Miller. I respect your opinions and will give that information careful consideration. But, for now, I'm in the camp that small shot behaves very similar to a fluid when passing through a venturi. I cannot explain the phenomenon you described with the full choked vs the cylinder bore, in the pendulum gun, but since the internal velocities cannot be measured (yet), and since the experimenters couldn't explain it either (so far the only explanation for this was ..........) I'm thinking that there could be another explanation as of yet not put forth.

Since there seems to be no absolute proof of either theory, yet ............. it's only our opinions, I guess. I will be pondering the recoil phenom for some time. It's fun to think about. If I can find any supporting work for my statement in the above post, I will surely post it.

The bulges in the thin barrels could be attributed to large size shot, in the absence of the shot sizes being contained in the data, which certainly might not pass through the constriction as freely as smaller shot. This has been noted for many years.

SRH


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Stan now you know how Hillary Clinton felt when she got cornered in the Bengasi cover up and with eYes crossed made the statement...

"At this point does it really matter ?"

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Originally Posted By: 2-piper
Quote:
It would be interesting to make a barrel without a forcing cone and choke so that the shell case would fit the chamber more like a rifle and the shot charge could enter the barrel unimpeded.


They did that, called it a Chamberless gun, they did though normally have a choke.
M/Lers had no forcing cone & most were cylinder bore. They, of course, did not use a case. They both shot extremely well.

Bore area is proportional to the Square of their diameters, therefore the 12 ga bore has about 40% more area than the 20 & about 75% more than a 28. If you fire for instance an ounce of shot out of each @ 1200 fps, you have indeed applied the same amount of Work. The Pressure to move the load to that level will though be 75% more for the 28 & 40% more for the 20 than for the 12, all figures in PSI or pounds per square inch. PSI is what deforms the shot, NOT total work.

Note also this pressure is NOT meaning the peak pressure but the total pressure applied. Even if by use of a slower burn powder we bring the Peak pressure of the smaller gauge down to a similar level to the 12, that pressure will be maintained for a longer period of time.

"IF" we were talking Static pressure then the applied time would be meaningless, but for the milleseconds involved here it does in fact become meaningful.


Interesting. It's certainly true that under both SAAMI (US) and CIP (European) standards, the maximum average pressure (MAP) for 12ga is lower than the 20ga MAP. But looking at the Alliant Powder website and comparing 1 oz loads, I can find a 12ga load with a peak pressure of 10,870 psi and a 20ga load with a peak pressure of 10,300 psi. Depends on the components used in both loads.

How does one go about determining the total pressure for a given load? When comparing MAP, while the 12ga standard is lower than the 20ga, the difference--SAAMI 12ga MAP vs 20ga--is only 500 psi (11,500 vs 12,000). That's nowhere near 40%.

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