Chicken or egg? Cartridge pressure, case specs or gun specs?

[rpenmanparker]

I'm trying to understand how cartridges acquire the pressure limitations which are associated with them. What determines the number? Is it the ability of the guns to handle the pressure, the ability of the case to handle the pressure, or a selection made for other reasons and the case and gun have to be designed to withstand the specified maximum?

When I see that the max. pressure of the .45 ACP is much lower than the 10 mm I can't figure out how that came to be. Were guns not as capable at the turn of the 20th century so the case size was restricted to limit the powder charge to the manageable amount? Or was that all the pressure that could be generated with the amount of powder that would fit in a predetermined size .45 ACP case and the case walls and guns were just designed to tolerate that. Then 10 mm came along with a 50% higher maximum pressure. How did that happen? Guns are stronger now? Or that is just what was desired and everything else followed that decision.

And what is the pressure specification protecting, the gun, the case, both?

So I ask, "Chicken or egg?"

 

[Scooter22]

I believe it is the original specs when the cartridge was developed. Plus they take into account old guns still being used. Obviously things change. Look at the 45-70. It was originally in a very weak firearm compared to these days. Put in a modern gun and it can take anything in North America and probably Africa.

 

[rpenmanparker]

I believe it is the original specs when the cartridge was developed. Plus they take into account old guns still being used. Obviously things change. Look at the 45-70. It was originally in a very weak firearm compared to these days. Put in a modern gun and it can take anything in North America and probably Africa.

Okay, but what does that mean? The .45 ACP case wasn't made longer to accommodate more powder because the original guns made for it couldn't take the pressure? Or the "desired" ballistics for the round simply translated to that much powder and therefore that size case? See what I mean? What came first?

 

[ATLDave]

You are assuming that there is a single reason or direction to this. There's no "grand plan" of gun or cartridge design.

Stepping back, we can say this: First came black powder. When smokeless powder was introduced, it had the capacity to easily generate too much pressure for black powder guns. Improvements in metalurgy and strength of design were required. As time went by, metallurgy continued to improve. Things like heat treatment of the steel can vary for a revolver intended for .357 magnum use versus .38 special use. Simple amount of material matters, too... a 1911 made out of the same material but chambered in .38 super will probably have a much higher actual pressure-at-failure than one chambered in 45 because the 38 barrel and chamber are the same outside diameter, but have smaller holes drilled in them and consequently it has thicker walls.

 

[reddog81]

Black powder cartridges pressure would be limited by the size of the case and how much powder can be stuffed into a case. This makes loading for black powder cartridges easy and provides an easy answer to your question with respect to the older cartridges. Since guns from this era still exist, the cartridges like 45 Colt, 38 S&W, 45-70 and to some extant 22lr still need to meet the same pressure requirements or be labeled as a +P round as is the case for 45 Colt or high velocity for 22's

45 ACP is probably a relatively unique in that it was developed as by John Moses Browning as one of the first auto-loading handgun cartridges right after the turn of the 19th century. The original load was developed to mirror the 45 Colt round and got pretty close with a much smaller case. Modern 45 ACP guns can typically handle much higher pressure thresholds due to both improved metallurgy and better designs. Most well used Colt 1911's from the WW1 era have the slide and barrel replaced due to battering of the various metal parts through the use during 2 World Wars. Most 1911's built today can withstand much more pressure and are chambered in 10MM and can be upgraded to 45 Super with a few modifications. And then there are guns like the HK45 that are built to handle 45 Super without any modification.

A lot of the new handgun rounds coming out now a days are modifications of older cartridges with slightly longer cases and higher pressure i.e. 32 S&W to 32 S&W Long to 32 H&R to 327 Federal Magnum. Of course you also have 40 S&W which was a modified 10MM case and is less powerful, however the shorter OAL and less pressure allowed it to be used in guns with a small frame.

As you can probably see there are a number of different reasons for how cartridges came about and each one is somewhat unique.

 

[Scooter22]

It means what I said. Theres variations on all cartridges that change over the years. I see this thread closing also.

 

[jmr40]

There are lots of reasons. For one thing a pistol in 10mm has more steel surrounding the chamber than a 45 in common guns which means more strength.

And steel 100 years ago wasn't as strong as it is today. Plus smokeless powder was relatively new in 1905 and early smokeless powder cartridges were loaded conservatively. The 30-06 is a prime example. It was initially put into use in 1903, then modified in 1906. By 1925 when the 270 was introduced gun makers had a better idea what smokeless powder could, and couldn't do and the 270 has traditionally been loaded to higher pressure. But in modern rifles there is no reason why 30-06 can't be loaded to the same pressure as 270.

For that reason the 30-06, and several other cartridges can safely have their performance improved by hand loading as long as the loads are used in modern guns. It isn't hard at all to get another 200 fps over traditional 30-06 factory loads with some hand loads, and perfectly safe. But more modern cartridges, such as 300 WSM it is hard to beat factory loads with hand loads.

And in some cases modern rifles chambered in older cartridges will handle higher pressure, but the brass designed for those cartridges won't handle the pressure without splitting.

 

[Texas10mm]

Also at the turn of the century the number of smokeless powders was few and what was available didn't have the energy content of many of the new powders...or had too much energy content for older guns.

 

[rpenmanparker]

There are lots of reasons. For one thing a pistol in 10mm has more steel surrounding the chamber than a 45 in common guns which means more strength.

And steel 100 years ago wasn't as strong as it is today. Plus smokeless powder was relatively new in 1905 and early smokeless powder cartridges were loaded conservatively. The 30-06 is a prime example. It was initially put into use in 1903, then modified in 1906. By 1925 when the 270 was introduced gun makers had a better idea what smokeless powder could, and couldn't do and the 270 has traditionally been loaded to higher pressure. But in modern rifles there is no reason why 30-06 can't be loaded to the same pressure as 270.

For that reason the 30-06, and several other cartridges can safely have their performance improved by hand loading as long as the loads are used in modern guns. It isn't hard at all to get another 200 fps over traditional 30-06 factory loads with some hand loads, and perfectly safe. But more modern cartridges, such as 300 WSM it is hard to beat factory loads with hand loads.

And in some cases modern rifles chambered in older cartridges will handle higher pressure, but the brass designed for those cartridges won't handle the pressure without splitting.

Very good explanation. Thanks. Using your example of 30-06 is the casing strong enough for the more powerful loads? Was the strength of the casing never the reason for the published pressure limit of the cartridge?

 

[lysanderxiii]

The strength of the cartridge case does have an influence on the maximum pressure limit. Remember that with a rimless cartridge case up to a tenth of an inch of the case is unsupported, or just sticking out of the chamber. And, there is a big difference between cartridge head designs and their strength, which will have a major influence on the maximum allowable chamber pressure.

Industry standards (SAAMI/CIP) try to limit maximum cartridge pressure so the weakest firearm chambered in that cartridge will not be dangerous.

You can probably up-load a .30-06 case to 85,000 psi and design a gun to fire it, but your average Remington 700 might have a shorter life with such a load.

So to answer your question:

Is it the ability of the guns to handle the pressure, the ability of the case to handle the pressure, or a selection made for other reasons and the case and gun have to be designed to withstand the specified maximum?

Yes.

 

[boom boom]

Very good explanation. Thanks. Using your example of 30-06 is the casing strong enough for the more powerful loads? Was the strength of the casing never the reason for the published pressure limit of the cartridge?

The reloading forum folks are the best to answer that-but -----

Usual effect is shorter life span on cases when using higher than normal pressure. Leaving aside grossly overpressured rounds, primer pockets get looser earlier, the brass gets brittle, cases can stretch depending on the chamber unless necksized, and so forth. Really high pressure cartridges get relatively few reloadings compared with lesser ones. .45 ACP being a low pressure cartridge, one can get many reloadings. A .44 Magnum, fewer.

Some folks even prefer once fired cases to load higher than normal pressure ammo as that weeds out the cases with unsuspected flaws and depending on the source can be cheaper to acquire. Some folks prefer to use only military brass or certain brands of brass (but the .30-06 military brass is getting pretty old now) for durability reasons as well as the case walls and web can be thicker.

Personally, I don't hunt nor fire rifles at uber long ranges so hotter and higher pressure loads simply mean shorter barrel, firearm, and brass life. Not really worth it to me. If it was, I would get the equipment that I needed and accept the shorter life of the stuff.

 

[rpenmanparker]

The reloading forum folks are the best to answer that-but -----

Usual effect is shorter life span on cases when using higher than normal pressure. Leaving aside grossly overpressured rounds, primer pockets get looser earlier, the brass gets brittle, cases can stretch depending on the chamber unless necksized, and so forth. Really high pressure cartridges get relatively few reloadings compared with lesser ones. .45 ACP being a low pressure cartridge, one can get many reloadings. A .44 Magnum, fewer.

Some folks even prefer once fired cases to load higher than normal pressure ammo as that weeds out the cases with unsuspected flaws and depending on the source can be cheaper to acquire. Some folks prefer to use only military brass or certain brands of brass (but the .30-06 military brass is getting pretty old now) for durability reasons as well as the case walls and web can be thicker.

Personally, I don't hunt nor fire rifles at uber long ranges so hotter and higher pressure loads simply mean shorter barrel, firearm, and brass life. Not really worth it to me. If it was, I would get the equipment that I needed and accept the shorter life of the stuff.

Thanks.

 

[rpenmanparker]

The strength of the cartridge case does have an influence on the maximum pressure limit. Remember that with a rimless cartridge case up to a tenth of an inch of the case is unsupported, or just sticking out of the chamber. And, there is a big difference between cartridge head designs and their strength, which will have a major influence on the maximum allowable chamber pressure.

Industry standards (SAAMI/CIP) try to limit maximum cartridge pressure so the weakest firearm chambered in that cartridge will not be dangerous.

You can probably up-load a .30-06 case to 85,000 psi and design a gun to fire it, but your average Remington 700 might have a shorter life with such a load.

So to answer your question:

Yes.

Got it.

 

[lysanderxiii]

Oh, and the wall thickness of the chamber is almost never an issue. If you calculate the minimum thickness required to contain 55,000 psi in a .5 in diameter chamber, you will be very surprised how thin it can be. The main reason for the thicker walls is for rigidity and heat absorption.

https://www.engineeringtoolbox.com/stress-thick-walled-tube-d_949.html

A 1911 barrel is more that capable of containing 50,000 psi, .45 ACP brass with 0.1" sticking out the back, not so much....

 

[rpenmanparker]

So why did I ask this question, the subject of this thread? I’m wondering about cartridges like .45 ACP. I guess from the answers I have gotten that the low maximum pressure spec was consistent in the early 1900’s with the firearms of that time. What I’m wondering is whether there is enough room in the casing to goose up the velocity significantly and compete more effectively with hot 10 mm loads. I understand that even if that were possible, it would be a problem if older guns got hold of such a powerful cartridge. Would a +P+ label provide enough of a barrier to misuse in such a case?

 

[Slamfire]

You need to read Vol IV of the Machine Gun by Chinn.

Chinn’s series at Hyper books:

http://www.ibiblio.org/hyperwar/USN/ref/MG/

This is not a simple question. Let me start off by saying that the cartridge case is the weakest link and has been the limiting factor in all action design. As Mike Walker's Rem M700 patent states:

BREECH CLOSING CONSTRUCTION FOR FIREARMS 2,585,195

Merle H. Walker, lion, N. Y., assignor to Rem ington Arms Company, Inc., Bridgeport, Conn., a corporation of Delaware Application

Prior art firearms of the type employing fixed metallic ammunition have always been dependent upon the metallic cartridge case for securing obturation with the Walls of the barrel chamber and preventing the rearward escape of gas from the barrel. As a result, the head of high intensity center-fire rifle cartridges has always been a massive chunk of brass of usually adequate strength to bridge over gaps between the end of the bolt and the chamber mouth, or clearance cuts for extractors, ejectors, and the like. However, in spite of this massive construction, the heads of cartridges, due to metallurgical deficiencies, barrel obstructions, or other difficulties, all too often fail in service, releasing white hot gas at pressures in excess of 50,000 pounds per square inch into the interior of the receiver. With some modern commercial and military rifles the effects of a burst head are disastrous, completely wrecking the action and seriously injuring or killing the shooter. One of the better known military rifles presents in alignment with the shooter's face a straight line passage down the left hand bolt lug guide groove, which, even though the receiver proper does not blow up, channels high pressure gas and fragments of the cartridge head into the location where they can do the most damage. It has been often, and truthfully, said that the Strength of most rifles is no greater than that of the head of the cartridges intended for use therein. The primary object of this invention is the provision of a firearm construction which is not thus dependent upon the strength of a cartridge head, ordinarily formed of a material of relatively low strength by comparison with the ferrous alloys used for the firearm structure.



This barrel comes from what is undoubtably the better known military rifle action mentioned in Mike's patent: the M1903. It is a poor action design, inferior in every aspect of departure from the M98 Mauser. A M1903 has the case head hanging out in a cone breech, absolutely no consideration for gas venting, and if the gas head ruptures, it blows gas directly into the shooters eye from a number of locations.



I have not uploaded even worse pictures of M1903 blowups. This one does have all the essential elements: the receiver ring blows, the stock split into pieces, because the action was designed with zero considerations for gas venting. A real "success orientated" program. We don't need to plan for problems because this is a "success orientated" program. Anyone else work on a Polly Anna program that failed? Anyone involved in the invasion of Iraqi?




A Mauser M98 barrel seats the case deeper, and uses the inner collar of the receiver to provide even more support.



Read Chinn, you will see stuff like this, explaining action design and cartridge support




The shooting community is nuts in many ways. It has to have the most high performance, highest pressure, no replacement for displacement, firearm on the market. Because with a lesser performance firearm, you might be robbed lobbing rounds at living creatures at unethical distances.



I am going to say, that pressure is not your friend. The pressure curve has an exponential slope and things go wrong sooner than later with any system operating at high pressures. Remember those driving movies "Speed Kills!". It is all true.

It is better to do the same job with lower pressures, if you are smart enough to figure out how to do that. I could go down a long list of possibilities, but in a large part, the legendary reliability of the M1911 is due to the fact they started off with a relatively low pressure cartridge that did not cause jams once temperatures got a little warmer, and did not require a structure of high quality alloy steels, and the mechanism did not beat itself to death.

We could learn a lot from the Chinese. Their service round operates just above 40,000 psia and is ballistically better at all ranges, in terms of trajectory and KE, than the 5.56. The cartridge has a lot of taper, thick rim, and probably functions with steel case materials. The 5.56 is a jam a matic with steel and not perfectly reliable with brass.



The current 5.56 cartridge is operating at a classified pressure, said to be around 65,000 psia. The proof test used to be 70,000 psia. Not a lot of margin there. Current M4's are going to be cracking bolt lugs even sooner with the latest cartridge, as the action was designed around a 50,000 psia round. And, from what I have heard, military barrels have so much free bore, to reduce pressures, they ought to be considered smooth bore. When you start off with a hot round, and then bump the pressures up, function does not get better, it gets less reliable. The US Military ought to hire some Chinese Engineers on their next rifle, or save a lot of development money and just buy the current Chinese service rifle and cartridge.

 

[Ironicaintit]

you may want to look through the archives, about the adventures of a member named "Clark".
He's done all kinds of destructive testing, regarding which calibers can be run real hot, and which chassis will handle it.
Truly astounding, what he's put firearms through.
especially his work with 380acp (a scaled down 45acp, innovated by JMB), made me think "oh wow, this guy is nuts"
it is some good reading, and worth the time spent.

you could run a load through a 45acp that would hold it's own, or surpass 10mm.... but you'd better be real sure what you run them in.

 

[Jim Watson]

The original .45 Colt Rimless Smokeless of 1905 was as close as Mr Browning and Colt could get to the .45 Long Colt in the action length of the pistol designs in production, but more like the .45 Gov't (Schofield) and .45 1909 than a Long Colt case full of black in a 7.5" Cavalry revolver. The similar .45 round specified in 1906 was a bit closer, increasing bullet weight from 200 to 230 grains. The ammo for the 1911 as adopted was not enough different to matter

Overloaded .45 ACP was fairly common in the pre-internet era; before you could easily look up pressure tested loads and get nervous.
Now we have legitimate +P, about a 10% increase in pressure; about a 10% increase in muzzle energy if the powder is chosen right.
I don't know of anybody advertising +P+ .45 but if there is any, there is no standard, just whatever they think the gun will stand.

If you want more power in the caliber and action, there is the .45 Super which is the same outside dimensions as .45 ACP but with beefed up brass for heavy loads in guns sprung and tuned for it. The .450 Triton was similar but with a small primer for even thicker case head. Out of production, I think.

The next step is the magnum treatment, very heavy loads in cases too long for the ACP chamber. Johnny Rowland seems to do a pretty good business with his .460 Rowland. Loads are so heavy that the gun must have a compensator to reduce the battering in recoil. The .451 Detonics is similar but not quite so hot as to require a comp. Extinct.

So, modern metallurgy and powders will take you farther.

 

[Englishmn]

.460 rowland conversion

 

[boom boom]

You need to read Vol IV of the Machine Gun by Chinn.

Chinn’s series at Hyper books:

http://www.ibiblio.org/hyperwar/USN/ref/MG/

Thanks for that link. Interesting stuff although I never really developed a positive appreciation for the machine gun after reading too much of stupid infantry tactics in WWI and their bloody consequences. I can appreciate the aesthetics and ingenuity of the designs but these weapons were designed simply to kill mass numbers of people quickly. It is their job and these do it well but I have no desire to own stuff like that.

The British at the Somme and the French at the Frontiers Battles in particular stand out for rank stupidity in charging fixed positions with plentiful German Machine guns.

Unfortunately, all organizations (and the military is no different) atrophy at the head and refuse to adapt to new conditions until the butcher's bill gets too much.

 

[denton]

As has been said, it's complicated. Ackley wondered in print how the maximum pressures were arrived at.

Back in the 1940s and 50s, the belief was that the CUP system read out directly in PSI. Read Ackley's books, and you'll find his loads listed in PSI even though he did his testing with a CUP system. When newer electronic measurement systems appeared in about the 1960s, it was found that the CUP system seriously underestimated actual pressures above about 40 KPSI. So engineers that had been working out bolt face force and hoop strain on barrels using the old measurement system were working with faulty data to begin with.

Sometimes there were issues other than science at work. The spec on the 270 is 65 KPSI, but if you check load data, most loads stay respectfully short of that limit. One might suspect overly enthusiastic marketing for that one. The spec for 7x57 is absurdly mild for a modern firearm in good condition, but that's probably necessary if you're making commercial ammunition that might be used on a weak wartime action. The 5.56 does indeed operate at about 65 KPSI (It's not secret info.). So how do we explain the 223 Winchester being specified at 55 KPSI? Some of the choices that have been made simply make no sense.

What it comes down to is this: The specifications we have are used for millions of rounds per year. Behind many of those specs, there is sometimes less science than you might imagine. What we have is a set of rules that experience has taught us provide satisfactory performance, safety, and economy, with a minimum number of stuck cases and loose primer pockets.

Congratulations. You're the canary in the coalmine.

 

[boom boom]

As has been said, it's complicated. Ackley wondered in print how the maximum pressures were arrived at.

Back in the 1940s and 50s, the belief was that the CUP system read out directly in PSI. Read Ackley's books, and you'll find his loads listed in PSI even though he did his testing with a CUP system. When newer electronic measurement systems appeared in about the 1960s, it was found that the CUP system seriously underestimated actual pressures above about 40 KPSI. So engineers that had been working out bolt face force and hoop strain on barrels using the old measurement system were working with faulty data to begin with.

Sometimes there were issues other than science at work. The spec on the 270 is 65 KPSI, but if you check load data, most loads stay respectfully short of that limit. One might suspect overly enthusiastic marketing for that one. The spec for 7x57 is absurdly mild for a modern firearm in good condition, but that's probably necessary if you're making commercial ammunition that might be used on a weak wartime action. The 5.56 does indeed operate at about 65 KPSI (It's not secret info.). So how do we explain the 223 Winchester being specified at 55 KPSI? Some of the choices that have been made simply make no sense.

What it comes down to is this: The specifications we have are used for millions of rounds per year. Behind many of those specs, there is sometimes less science than you might imagine. What we have is a set of rules that experience has taught us provide satisfactory performance, safety, and economy, with a minimum number of stuck cases and loose primer pockets.

Congratulations. You're the canary in the coalmine.

Well, you can spend the $700-1000 for piezo electric strain gauge systems and determine pressure levels via psi in your own firearm. Believe it or not, prices are a lot better than a few years ago.

https://www.shootingsoftware.com/pressure.htm

 

[reddog81]

So why did I ask this question, the subject of this thread? I’m wondering about cartridges like .45 ACP. I guess from the answers I have gotten that the low maximum pressure spec was consistent in the early 1900’s with the firearms of that time. What I’m wondering is whether there is enough room in the casing to goose up the velocity significantly and compete more effectively with hot 10 mm loads. I understand that even if that were possible, it would be a problem if older guns got hold of such a powerful cartridge. Would a +P+ label provide enough of a barrier to misuse in such a case?

The powder in the 45 ACP case takes up maybe a third of the space in a case. With fast burning dense powders it would be easy to accidentally fit a double charge into the case. The 45 Super and 460 Rowland are basically your 45 ACP +P+ and beyond.

 

[Texas10mm]

A good example of how the brass is the weak link would be the .327 Federal magnum. It's just a lengthened .327 H&R Mag which is a lengthened .32 S&W Long which is just a lengthened .32 S&W.

The .32 S&W was a black powder cartridge.

The .32 H&R has a max pressure of 21k CUP, the .327 Federal mag has a max pressure of 45k PSI, that makes it one of the higher pressure straight wall handgun rounds. The web, or base, of the brass is much thicker. So thick that some dies for the other .32 revolver rounds can't be used for the .327 Federal.

 

[ATLDave]

A good example of how the brass is the weak link would be the .327 Federal magnum.

Well, I dare say that if you ran a .32 S&W up to 45k PSI in an old Smith & Wesson I-frame from 1905, if the brass were all that failed you would be very lucky. You'd almost certainly blow the cylinder to pieces and the top-strap as well.