Why is automatic pistol cartridge case so long?

[alvin]

It's not a Luger question, but it's pistol cartridge case length related.

People doing reloading may notice pistol cartridge is way longer than necessary from holding that little bit smokeless gunpowder point of view.

Same is true for revolver cartridge. For revolver, I would guess it's related with backward compatibility, the sze was designed from black gunpowder days. But for automatic pistol cartridge, they were designed for smokeless gunpowder, why were they all so long? Won't a shorter cartridge case at least saving some brass?

I thought over and over again, but I could not find a reasonable explanation. Could you help?

[Vlim]

It regulates the pressure. The extra space inside the cartridge helps the gasses that form during ignition to expand to a certain level before forcing the round out and into the barrel. It also acts as a fail safe that prevents that gas pressure inside the cartridge will become too high with unwanted effects on the pistol and shooter. At least, that's my point of view and it may be horribly wrong

[alvin]

Thanks Vlim. With all my respect, I am a little bit doubtful on it, because rifle cartridge is more filled. So we don't frequently hear overloading a rifle cartridge and it explodes, not much extra empty space inside. For pistol cartridge reloading, it's very easy to overload.

[Vlim]

Yes, but you have to remember that with the early development of the auto pistol, they were pioneering, trying to scale down a rifle round to a pistol format. Just like mammal evolution leads to unnecessary byproducts, so does technical evolution, like the toggle lock which proved to be useless and was dropped.

[A.Mifsin]

As I know it, when you reload any cartridge it must be loaded 90% of the volume minus the bullet seated.
One has to check what the volume left is after the bullet is seated than use the right powder that gives 90% of fill otherwise it could build extra pressure which is very dangerous.
Then there is compressed load which is also very dangerous. Better refer to a loading manual before you try to reload.
Alf.

[Vlim]

I had the pleasure of closing the hole caused by a piece of case brass in the forehead of an unexperienced reloader about a year ago. Besides stuffing the bullets (.357 magnum) to the rim with powder, his loader also used powder that hat become wet and had deteriorated to a very fine pulverized powder. The pressure was large enough to crack the cylinder in half, blow the bridge off the revolver and logde part of the brass case in the shooters forehead.

I removed the remaining rounds from the other cylinder half, pulled the bullets and examined the powder. Of the 2 rounds, one was ok, the other was also an accident waiting to happen. The cause was mainly a shipment of powder gone bad, but also lack of care and knowledge during reloading.

So the 'breathing space' in a case is definitely there for a reason

[A.Mifsin]

"So the 'breathing space' in a case is definitely there for a reason "

Yes it is, and it is very important for consistency ammo, otherwise each round will have different velocity.

Alf.

[PhilOhio]

I hesitate to differ with some very knowledgeable people here, but unoccupied air space in a cartridge is not a desirable thing and is most assuredly not intentionally incorporated as a safety feature. You want as little air space as possible, ideally none.

This issue has been examined to death by military and civilian interior ballistics laboratories, including the H. P. White Laboratory, for quite a few decades. They have reached the conclusion which I adopt, above. Many lengthy papers have been written on this.

Military rifle ammunition is loaded to fill the case as far as possible without compressing the powder charge during bullet seating. They want the least empty air space possible.

As you reduce powder charge in a given case, accuracy begins to drop off; first a little, then a lot. The degree varies with powder type. But there comes a point where significant pressure variations are measured, i.e., high pressure spikes. Reduce the charge just a bit more, and you can blow up the gun. This is not a theoretical problem, and there are very specific warnings with certain cartridges and powder types. These are published in all reloading manuals. So more air space creates more danger, not less. And this is not about the risk of stuck bullets in revolvers; that's a separate issue.

The very design of modern cartridge cases focuses on creating just enough internal volume for a given weight of a specific type of powder to burn and generate pressure, within a narrow range, to drive a bullet of a certain weight at a certain velocity. It's quite a balancing act, and it does not include allowing for extra sir space...except, as I mentioned, to avoid compressed powder charges. But even that is sometimes O.K., with certain powders and within known limitations.

A recent example of such major design effort was when our military switched from the .30-06 round to .308 Winchester, aka 7.62mm NATO. The intent was to create a round which would be shorter, would feed better in automatic weapons, and would give almost the same external ballistics as its parent. And minimal unoccupied internal space was part of the target criteria. They got all of it right...as they later did with the 5.56mm service round; minimum or near zero air space.

This air space is an interesting thing to me just now, as I have been battling it for the last month; trying to make my .45 Long Colt cartridges shoot as accurately as those of two of our major ammo manufacturers, who are very secretive about the powders they use. This case was designed around black powder, and it performs very poorly with most loads of most types of smokeless powder, using any bullet weight at all. Many have tried to beat this and few succeed. Working on it today, in fact, once I stop playing with this computer.

Oh yes, there is a powder called "Trail Boss", I believe, which was specifically developed to fill up black powder legacy cases such as .45LC and .44-40 (.44WCF) to get rid of all the problems created by unwanted internal air space resulting from the use of higher density/lower volume smokeless powders. Still trying to find a local source.

I just wanted to cover this so any of you who reload would not be trying to get more air space. But don't be worried if reduced loads give you some. Powders including Bullseye, Red Dot, Unique, and others used for Luger ammo are not so critical with air space; you will absolutely not get those high pressure spikes with reduced loads. Such powders as Alliant 2400 are another story, if you back off too far in such things as .44 Magnum. But 2400 is not a Luger powder.

[A.Mifsin]

When I mentioned 10% space in the shell I was referring to a pistol shell as the question was about â??Why is automatic pistol cartridge case so long?â?�
I agree that too much space in the case is very dangerous for both rifle and pistol.
That is why I recommended a loading manual because there is a vast loading date and very different opinion about this subject
Regarding rifle shells yes it is better and safe to fill the case, but compressed charge is dangerous on both pistol and rifle.

Alf.

[alvin]

I thought the historical reason that Vlim mentioned earlier again.

There is still one unexplanable.... say early automatic pistol cartridge was shrinked down version of rifle cartridge, so came the longer than neccessary length. Why did those late auto cartridge, e.g. 9x18 Markarov, still being long ?

And, Phil mentioned air space is not good. Could there be something else? All those designers go long cases, there must be a reason...... Is there any change in smokeless powder formula over years, so old filled case now becoming empty because more new powder being used nowadays ?

[Vlim]

Change of powders, change of techniques, change of ways to measure pressure levels, etc...

The modern powders certainly differ from the older ones. Early DWM stuff was a more slow burning powder, creating a pressure curve that differs from those generated by modern fastburning powders.

The firearms technicians from 100 years ago were not idiots, but they lacked access to equipment and data that is available now. Even as late as the 1970s, companies like Mauser struggled to get the ballistic data they needed.

[Ron Smith]

"So we don't frequently hear overloading a rifle cartridge and it explodes, not much extra empty space inside."

Alvin,

You can very definitely, and easily overload a rifle cartridge. That's one reason why they make powder tricklers for reloading rifle cartridges. Just a very few additional grains of powder in a high intensity rifle cartridge can make your day suck.

I recently saw a .338 Short magnum (one of the new hyped magnums) bolt action, rifle that was locked up so tight that it had to be beat open with a hammer. The case had separated 1/4 ahead of the rim (looked like it was cut with a torch) the remainder of the cartridge had to be reamed of of the chamber.

The owner and reloader, had his thumb over the vent hole on the left side of the receiver. The escaping gas blew / burnt a 1/8" hole complelely through his thumb, exiting at the base of his thumb nail.

He is very luck that he was using a good quality rifle, and it held. He could have lost his hand, or much worse.


Reloading / handloading isn't something to take lightly.

[PhilOhio]

I forgot to mention one important point, regarding the dangerous high pressure spikes which occur with the use of certain types of powders in various cartridge cases when charges are reduced and air space is increased. The best ballistics people, with access to the best laboratory equipment still do not know exactly why it happens. Some have theories, but nothing more. It really is a more complex question than it appears. But I'm a believer and I take their advice.

A. Mifsin,

You said, "...but compressed charge is dangerous on both pistol and rifle..."

My gut feeling is that I agree with you, but sometimes the ballistics professionals do not. Just about all of the reloading manuals list compressed charges for both rifle and handgun cartridges. If their lawyers thought it was unsafe, the recommendations would not be published. But compressed charges make me uncomfortable, and I refuse to load them.

Vlim, Ron, guys,

Yes, there are lots of historical reasons we have cases which are far longer than they need to be, to hold the necessary amount of modern smokeless powder. And in some designs, length helps in feeding and handling of the empty.

But all of the empty space and pressure questions get back to the essential wisdom of never straying from recommendations in the published reloading manuals. In close to fifty years of reloading, I was "forced" (by my own impatience, I suppose) to do it once, in developing a load for an obsolete military automatic weapon for which no such information was available. Nor were the original powder types. I drew upon my own experience, which I thought was pretty extensive, used my own judgment, and relied upon information relating to a nearly identical cartridge used for a nearly identical weapon operating in the same pressure range. I was wrong, and I still do not know why. On the second round, the case head separated. No great damage was done, and I did successfully work up a load, but I was humbled. I haven't strayed from taking my own more cautious advice in the succeeding 20 odd years.

The bottom line is that the science of ballistics is still not a discipline where everything is known about everything. There is no substitute for a laboratory, a pressure gun, good sensors, software, and computer equipment when developing a new load or cartridge type...after all the calculations and predictions have been done.