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Miller, which of the three volumes of Sir Gerald's did you have?

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King;
I had a boxed set which was published around 1960/61, don't recall exactly now. It had all three volumes. Two of the volumes were combined into one book so was actually only two books, but had all three volumes.


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Quote:
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%.


Larry; First & Foremost that 11,500 vs 12,000 is Max Peak Pressure "NOT" Max Average Pressure. Average pressure will be way lower than the Peak. Using my same example if one pushes an oz of shot out the end of a barrel @ 1200 fps it takes a certain amount of work to be applied regardless of the size of the bore. In a shotgun the pressure rises very rapidly to its peak while still in the chamber & then falls, also quite rapidly at first & then slower as it goes down the barrel, giving the typical pressure Curve I am certain you have seen many times. The Average pressure is the total pressure under that curve. That work which is done, or Force, is proportional to the pressure times area. Since the 12 gauge has 40% more area to push on the 20 gauge has to use 40% more pressure to accomplish the same Force.

Again. FORGET the Peak pressure here, we are talking about the entire pressure curve for the total length of the barrel. Even within the same gauge, one can push the same shot load to the same velocity with widely varying Peak pressures. Keep in mind though one has not actually Lowered the average pressure, only Re-Distributed it.

An older Hercules handbook I still have has a chart showing the length of the column for one ounce of shot in the various gauges. for a 20 gauge they show 0.968" & for the 12 0.690". Divide .968 by .690 & guess what you get, a 40% longer column. This based on an ounce of shot occupying 0.288 Cu In of space.

That same 0.288 CuIn will also, depending upon exact granulation & density, contain 2˝ drams of Black Powder.


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I know Longshot powder kicks the snot out of me...certain other powders are much more comfortable.

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Have you Chronograph tested those Longshot loads in comparison with the "Other Loads"? Unless you know with absolute certainty the velocities are equal then just saying one powder Kicks Harder than the other is not really saying much.


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I tend to agree with Geo’s comments in regard to this latest article in SSM magazine from Roster.

At times I have found Roster's articles informative. That said, I have also come to the opinion that at times Roster has used his article space in SSM to promote his own agenda.

Being a long time subscriber to SSM a concern to me are the recent actions/directions/decisions that Mr. Stuart seems to be taking SSM.

I heard that Diggory Hadoke was developing a new online magazine. I am looking forward to reading/seeing the content.

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Originally Posted By: 2-piper
Quote:
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%.


Larry; First & Foremost that 11,500 vs 12,000 is Max Peak Pressure "NOT" Max Average Pressure. Average pressure will be way lower than the Peak.



Nope. I'm quoting straight off the SAAMI Voluntary Performance Standards, Miller. Max Avg Pressure for 12's is 11,500; Max Probable Lot Mean is 12,000; Max Probable Sample Mean is 12,800. For 20ga, either 2 3/4" or 3", the figures are 12,000; 12,600; and 13,500.

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Larry;
First & Foremost you have to "Understand" what you read & Cite. Yes, the pressures quoted are an "Average" of Max peak pressures. I apparently wrongly;y ASS-U-MEd that everyone here understood that.
All pressures unless one is only talking of a single shot are averages.
I specifically Stated I was NOT speaking of peak pressure, BUT of the total pressure for the length of the barrel, which is also an average when a number of shots are fired. The Clue there in what you posted is the WORD MAX, which again, I Specifically stated was not what I was speaking of.

What part of that is Beyond your Comprehension, Do Tell, & I will type real Slow & try once more to explain so maybe you can read it well enough to Comprehend.


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Miller, if you hadn't started by apparently being unfamiliar with SAAMI terminology--which I copied directly from their data--you wouldn't have been confused. SAAMI, being primarily concerned with maximum pressures (proof or service), starts out by listing Maximum Average Pressure. Which is, as far as I know, the number to which reloaders pay attention since they don't want to exceed the Max Avg Pressure for the gauge in question as determined by SAAMI. Reloaders have no idea of the "total pressure" and have no way of measuring it. The best they can do is look at a reloading manual or website and the pressure stipulated in that manual or website. If they're not worried about the pressure stipulated in the book, then they proceed to reload. It's not really rocket science.

Referring back to Mr. Roster's article: Many of us are aware of the fact that the CIP standard service pressure (10,730 psi) is lower than the SAAMI service pressure (11,500). So if we're dealing with CIP guns proofed to the CIP standard, we shoot for a lower number. Likewise, the SAAMI standard was lower for short chambered American shotguns than it is for modern guns, which gives us yet another reason to seek out loads that one may not necessarily define as "low pressure", but are certainly lower pressure than the 11,500 psi we might get if we were to touch off a modern American factory 12ga shell.

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Larry;
I was NEVER confused at all. I stated plainly Up front what I was speaking of which was the average TOTAl pressure, over the entire length of the barrel. Totally UNRELATED to MAX Average pressure as given in the SAAMI standards you quoted.

So far as I can tell you are the only one here who Simply Does Not Have a Clue as to what you are even saying on this thread.

I even said I was speaking of the entire area under the pressure curve, which again is totally unrelated to the Max Peak pressure.

The fact that all quoted pressures of this sort are never a "ONE-SHOT" deal but the average of a number of shots is again totally unrelated.

Once more this is extremely simple, What Part are you not Capable of Understanding.

Last edited by 2-piper; 06/19/19 09:56 PM. Reason: Left the S out of SAAMI

Miller/TN
I Didn't Say Everything I Said, Yogi Berra
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