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I notice in most of my reloading charts that the maximum pressure for .45 is 20,000 psi whereas other calibers may go as high as 35-40,000 psi. I have a couple of questions arising out of this.

1. What allows higher pressure in some calibers; is it case design or barrel design or both.

2. How high of psi can a .45 safely operate at?

3. Are there any formulas or charts that relate charges and seating depth variables to the resulting pressure?

Thanks
 

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One could spend quite a bit of space addressing your questions, but we will try to summarize.

The primary factor in design pressure is the chamber of the firearm. Within a given chamber design, the case is usually the weak point in the system. But there are exceptions to both of these generalizations.

The chamber shape has an effect, as in the .45 auto where the feed ramp leaves a part of the case unsupported by the chamber, so that the case must bear the entire load at that point.

The thickness of the chamber and the material determine the strength of the chamber. For instance, a Ruger Blackhawk in .45 Colt will withstand a lot more pressure than a modern Colt revolver, which, in turn, can withstand more pressure than a 100-year-old Colt revolver.

The action type has an effect also. A bolt action is inherently stronger than a lever action, for instance, though improvements in design can reduce the difference.

In the past, different case designs had an effect on the pressure a cartridge could stand, but modern cases are more or less equally capable for their design cartridge. However, cases for one cartridge may be considerably thicker than for another cartridge, and therefore capable of withstanding higher pressure. The design pressure of the 300 Winchester Magnum, for instance, is considerably higher than some apparently similar cartridges.

In earlier days, a countersunk revolver chamber could withstand higher pressure than a non-countersunk chamber, but modern cases have made this distinction obsolete.

As mentioned earlier, this is a complicated subject, and an overview may not be very helpful. Suffice it to say that there are people who load cartridges well beyond design limits. Some of those experiments have led to changes in specifications for cartridges, where the cartridge had more capability than had traditionally been recognized. Other of those experiments led to missing fingers and worse.

The issue is much too complex for there to be charts or formulas relating charges and seating depths to pressure. Sometimes changes have a linear effect, and sometimes they are dramatically nonlinear. Some powders, for instance, burn faster as pressure increases, which makes for some startling pressure increases with relatively small powder increases.

At the other extreme, it has finally been proven that an overbore rifle cartridge, in a barrel with throat erosion, loaded with a much reduced charge of slow burning powder can detonate and demolish the firearm. Contrary to misinformed opinion, this does not happen in pistol cartridges.

All these complicated factors indicate why it is so important to follow loads developed in laboratories and published in reliable manuals rather than striking out on one's own.

Unless one has a PHD in metallurgy and a laboratory at hand, it is best to stick with published design pressures.


[This message has been edited by KLN (edited 11-20-2001).]
 

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Sorry . . . This forum requires that we don't launch personal attacks. OK. We won't launch a personal attack against Clark.

CLARKS *DATA / METHODS* ARE GROUNDED IN NOTHING MORE THAN SIMPLE OBSERVATION.

Observation is NOT engineering with respect to load specifications and metalurgy. As a further caveat, let me suggest that you refer to Clark's posts in www.hardcoretalk.com where he regularly "boasts" about calibers he has "abused."

Clark's *METHODS* typically consist of buying tired, old, marginal firearms and then proceding to systematically over stress them with excessive loads until they fail.

Let me offer a simple analogy here:

Take a coat hanger and bend the wired back and forth several times. Set it aside.

Take a second hanger and bend it back and forth twice.

Now take the first hanger and bend it twice, like the second hanger.

Repeat. Repeat. Repeat. Repeat until one of the hangers "fails" and the wire breaks from work hardening.

What this demonstrates is that hangers are different. Pre-existing stresses to hangers result in metalurgical changes in the molecular structure of the hanger steel. These stresses are NOT apparent in the hangers until they "fail" . . . not at least visually apparent. Nonetheless, the metal changes during each stress application until finally the metal fails.

Similarly, the metalurgical structure of a firearm that is exposed to excessive load wil change, resulting in a shift in the "base line" characteristic of the metal being stressed. Subsequent stresses do NOT reflect application of load to a base-line metalurgical characteristic, but rather reflect load bearing characteristics of metal which has been systematically stressed and over loaded.

Predicting load response in such a model is like shooting at a moving target.

Clark might be a nice guy. I'm betting he's a nice guy.

But his methodology is crack-pot. It's dangerous. It's unreliable. And mostly, it results in worthless and non-repeatable data.

But back to the question at hand:

The difference between a firearm chambered for 44 Russian and a 44 Magnum in terms of load bearing design is just that -- load bearing design. This is why you don't shoot smokeless powder in black powder firearms, why anything relating to ammo warns that it is intended to be used in "modern firearms in good working order" and that "failure to use as recommended may result in personal injury or death."

YES Clark . . . modern reloading manuals provide data that provides a considerable margin of safety. Modern reloading manuals are published with the "weak link" in mind -- considering ALL the design/component failures that might be assembled into any given load. And there are considerable variables.

YES . . . It's entirely possible to load a modern firearm substantiall beyond published data and still not blow it apart.

BUT -- when firearms fail, they fail without warning. Sometimes you get lucky and the damage is limited to the firearm. Published data hopes to contain failure to the damage of the firearm.

HOWEVER . . . when one exceeds published load data, one introduces numerous variables into the equation. Clark would like to think that he has considered all the variables and that he as "engineered" his "tests" to measure these variables.

Unfortunately, Clark fails to appreciate the complexity of his equations. So far he's been lucky. So far . . .
 

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Genghis, I believe your post has had the desired effect.

When Clark posted data previously it included pressure data for the overloads. I asked what sort of pressure testing equipment he was using, and he admitted he had none. That led me to conclude that the "data" would be of no interest because of technical irregularities to those who understood it, and could be dangerous to those who did not understand it.

It is best not to have it posted to a forum where new reloaders are attempting to get sound advice.

Well done.
 

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A couple of points:

(1)The various specifications for cartridges have been arrived at by experimentation, and codified for you and I to simplify safe firearm operation. There is no need to learn the hard way, which can be fatal.

(2)Clark and others over the years have experimented with discovering the absolute limits. The data is very interesting and appreciated and of educational value. This becomes some of the group "wisdom" we can draw from.

(3)Very little is gained by pushing a cartridge/firearm up to or slightly past it's SAMI-specified limits. Why? because the limits take into consideration not only a number of technology issues, but also firearm application. I.e. the .45acp was designed for use in a small, portable, hand-held, pistol capable of rapid shooting at close ranges against people. There are many other cartridge/firearm combinations better suited for 300yd shots at elk.

(4) Published load data may very well be far below the maximum SAMI pressure. Why? (a) the best accuracy/shootability point was arrived at below max and (b)unfortunately Slime & Rodent, attorney's at law do exist, and very willing to take a case representing the estate of a nitwit reloader who wouldn't bother to get educated on the limits.

(5) There is a lack of published limits for reloading. E.g. if you use a powder manufacturer's load data and OAL, but you produce a cartridge with an OAL .020" shorter than specified, should you throw it away/pull it? Or is it safe? Often load data is pretty sucky and it doesn't matter whether it comes from an expensive manual or from the internet. This is where group experience/wisdom is helpful.

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Have a great day!
 
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