9mm, 40S&W, 45ACP.... which is really the high pressure round

CanuckShooter

CanuckShooter

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I am a bit confused regarding the pressures of 9mm, 40S&W and 45ACP, and why some are designted as 'high pressure'. Was wondering if someone could help me out and explain it to me.

I always hear people talkign about how 40S&W is a very high pressure round, and as a result the brass does not last long, and to be careful reloading it, because it is very prone to kabooming (regardless of platform). Then there is the 9mm which is viewed by many as a much safer, lower pressure round.... even though when I am looking up the pressure ratings in my reloading manual, the 9mm has MUCH higher pressures than the 40S&W. Despite the significantly higher pressures, the 9mm has much lower recoil.

Then there is the 45ACP..... which has the reputation of being a very low pressure round, yet for example, the Glock, which was originally designed for 9mm, had to be beefed up a great deal to withstand the heavy battering of the 45acp round.

So to condense all this:

* 9mm = high pressure, regarded as much safer to reload than 40S&W, low recoil
* 40S&W = high pressure (though lower than 9mm), be careful reloading, high recoil
* 45ACP = low pressure, very safe to reload, but guns have to be reinforced to shoot it safely


All this kind of confuses me. I considering that the pressure in the average 9mm cartridge is about 3 to 4 times that of the average 45ACP cartridge, yet 9mm is still considered a safe cartridge to reload, and has far less recoil.

I know I am missing a huge piece of the puzzle here.... I just can't seem to find it anywhere lol
 
CanuckShooter said:
I considering that the pressure in the average 9mm cartridge is about 3 to 4 times that of the average 45ACP cartridge
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Where did you get this? 9mm runs at 1.6 times higher pressure than 45ACP.

First thing that might explain some of the mysteries you've encountered is that recoil is mainly a function of bullet weight, not chamber pressure. This explains why the .45ACP, which produces lower pressures than both the 9mm and .40S&W, still produces more recoil than those two.

9mm and .40S&W both run at 35,000 psi according to SAAMI standards. .45ACP runs at 21,000 psi: much lower.

In my experience, 9mm brass doesn't last any longer than .40S&W brass, but then again, brass life depends on lot of things.

I suppose (and this is just a theory) the reason .40S&W poses a greater risk to the reloader than 9mm is that it has a greater case capacity, therefore the risk is greater of dumping too much powder in there without realizing it. 9mm is usually full of powder so any overcharge overflows. By that same token, even though you assume .45ACP is inherently safer to reload, that cartridge presents a great risk of double-charging when using fast-burning powders.

Other than that, I also get the impression the 40S&W cartridge's potential danger has almost become mythical through the years and people just tend to repeat what they've heard. This could explain why you've been left with the impression that cartridge is more dangerous than others, when in fact, it really isn't.
 
As far as reloading the reason it is safer to reload 9mm is becasue the case is small and it would be hard to not notice a double charge. In a .45 case it is easy to put a double charge in the case and not notice, similar to .40 cal. . the pressure differences between 9mm, and .40 is only about 2500 psi with the 9mm being the higher pressure cartridge, but I think the weight of the bullet plays a role here. Someone more knowledgable than me should chime in anytime.
 
Cerdan said:
Where did you get this? 9mm runs at 1.6 times higher pressure than 45ACP.
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Oops... that should be a 2, not a 3. According to my books, the average full powered 45ACP cartridge is running at about 17,500CUP... maybe a bit less. The average full powered load for the 9mm is about 31,500CUP.

I figured it was some sort of F=ma type equation as far as recoil goes. Recoil forces directly correlating to the velocity and mass of the projectile. If mass goes up, the resulting force of the recoil goes up, and if velocity goes up, recoil goes up as well. I just don't get how all this is related to pressure.

It also seems that the size of the case, or empty space in the case is a huge factor in whether a cartridge is high or low pressure. I think THIS is the concept I am having a hard time wrapping my brain around.

I'm still looking it all up, and trying to put it together in my head.... :redface:
 
Here is an easy test for you. Go get 2 bottles of coke. a 600ml, and a 2l. Fill them both with the same amount of coke maby 300 ml. Shake em up. Which is gonna have more pressure. I used to load 9mm, and .45 acp rounds with the same amount of powder for ease of reloading. I had decent results, but have since stopped that. Same powder, same load, different case. Very different pressure.
 
i'm no expert but i will explain the mechanics of the recoil. this will help you understand the difference in recoil between the different rounds
for every action there's an equal and opposite reaction
so when the bullet is pushed forward, the firearm is pushed backwards
now the total momentum for each side is weight x speed.
it's the product of these two terms that has to be high to have a higher recoil
and for the same round, the heavier your firearm, the less your "felt" recoil will be
 
CanuckShooter said:
It also seems that the size of the case, or empty space in the case is a huge factor in whether a cartridge is high or low pressure. I think THIS is the concept I am having a hard time wrapping my brain around.
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Though you're right to say that case capacity plays a role in pressure, I wouldn't say that's what determines whether the cartridge is high or low pressure. Take 9mm (35,000psi) and 44Mag (36,000psi). One is tiny, the other is huge, but they generate very similar pressure.

There's no great mystery to it. A cartridge's pressure is only the result of its creator and intended performance. I'm having a hard time expressing myself (it's late... and I'm French!), but what I'm getting at is that the only thing that determines whether a cartridge is high or low pressure is what particular ballistics that cartridge was designed to achieve. For example, the .45ACP was designed originally to fire a 230gr. bullet at 850 ft/s. That was the goal. 10mm was originally designed to fire a 200gr. bullet at 1200 ft/s.

Resulting pressure is only ancillary, which is why you won't find any correlation, or logic, with regards to pressure as a function of case capacity, bullet weight or anything else.
 
Mardig... thanks, you were probably posting at the same time I was, and therefore didn't see my last post. I was aware of the F=ma equation, equal and opposing forces etc etc.... but was struggling with the pressure side of things and how it all tied in together. I think I was under the impression that pressure itself, directly influences recoil more that it actually does. If that even makes sense lol

Mlehtovaara... the pop bottle analogy was right on. Wow, I am embarassed, and stumped as to why I needed help on such as simple concept lol In the interest of saving face, I'm going to blame too much caffeine :redface::D
 
There are several issues at play. Presure has little to do with it.

The 40 S&W is a bigger case with more powder and and heavier bullet. Much more energy/power invloved. But the early generations of 40 pistols were on 9mm frames.

These frames took a bigger pounding and in some models, started to break. nothing to do with pressure.

The 45ACP is an even bigger case, with even more powder and a heavier bullet with even more energy and power involved - but the pistols were all designed from scratch for the 45 - so they take it just fine (unless they are aluminum frames).
 
I will see if a table including 40 S&W is also available.

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One thing that is very often confused is pressure and force. A lower pressure acting over a larger area can create more force than a high pressure on a small area.

For example. (simplified since the only pressure used below is the PEAK pressure)

9mm at 35,000 psi = 3,460 lbs of force pushing the bullet.

45 ACP at 21,000 psi = 3,349 lbs of force pushing the bullet.

40 S&W at 35,000 psi = 4,400 lbs of force pushing the bullet.


So the 9mm and 45 have about the same amount of force pushing the bullet out of the barrel. However since the 9mm bullet is lighter than the 45, the 9mm is accelerated to a higher velocity.
 
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There isn't really a direct correlation between between peak pressure and felt recoil. Recoil is a function of a bullet of a given mass being accelerated to a given velocity as well as a given mass of powder being accelerated to some given average velocity.

The principle at work here is conservation of momentum. The momentum of the bullet plus the powder will equal the momentum of the gun recoiling.

A more detailed explanation of the calculations can be found in Hatcher's Notebook.
 
SandRoad said:
One thing that is very often confused is pressure and force. A lower pressure acting over a larger area can create more force than a high pressure on a small area.

For example. (simplified since the only pressure used below is the PEAK pressure)

9mm at 35,000 psi = 3,460 lbs of force pushing the bullet.

45 ACP at 21,000 psi = 3,349 lbs of force pushing the bullet.

40 S&W at 35,000 psi = 4,400 lbs of force pushing the bullet.
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Very interesting. Do you have a formula to calculate force? I imagine it's a factor of pressure and area (volume?).
 
Cerdan said:
Very interesting. Do you have a formula to calculate force? I imagine it's a factor of pressure and area (volume?).
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Force=Pressure x Area

for your bullet base, Area = pi x r^2, or about 3.14 x r^2

For a 9mm, not counting engraving from the rifleing, you're looking at r ~ .335"/2 == .1775, so pi x r^2 is then ~ .0881"
 
the other point is WHAT IS THE GUN pressured for- the old average for the 45acp was not 21k, but 19 for the UNSUPPORTED - ie the 1911 - that was the point of building things like the 451 detonics, etc- the thicker RIFLE brass took a higher pressure than pistol before catastrophic head failure
 
The relationship between pressure changes inside the cartridge case and muzzle velocity is extremely complex. You can use a program like Quickload to help, you cannot use your brain by itself.
There are formulas to relate velocity, gun mass and bullet mass to felt recoil. The bullet/gas/unburnt powder leaves the barrel with a certain mass and velocity, what the pressure was a millisecond ago does't matter.

If you get hit by a 10 ton bus at 60kph, it doesn't matter if it is diesel or gas.
 
CanuckShooter said:
I always hear people talkign about how 40S&W is a very high pressure round, and as a result the brass does not last long, and to be careful reloading it, because it is very prone to kabooming (regardless of platform). Then there is the 9mm which is viewed by many as a much safer, lower pressure round.... even though when I am looking up the pressure ratings in my reloading manual, the 9mm has MUCH higher pressures than the 40S&W. Despite the significantly higher pressures, the 9mm has much lower recoil.

Then there is the 45ACP..... which has the reputation of being a very low pressure round, yet for example, the Glock, which was originally designed for 9mm, had to be beefed up a great deal to withstand the heavy battering of the 45acp round.

So to condense all this:

* 9mm = high pressure, regarded as much safer to reload than 40S&W, low recoil
* 40S&W = high pressure (though lower than 9mm), be careful reloading, high recoil
* 45ACP = low pressure, very safe to reload, but guns have to be reinforced to shoot it safely


All this kind of confuses me. I considering that the pressure in the average 9mm cartridge is about 3 to 4 times that of the average 45ACP cartridge, yet 9mm is still considered a safe cartridge to reload, and has far less recoil.

I know I am missing a huge piece of the puzzle here.... I just can't seem to find it anywhere lol
Click to expand...

Here's the piece of the puzzle you are missing:

Using proper loading techniques and modern components, NO ammunition is more dangerous or prone to kabooming than the next. The guns have all been designed to contain the energy produced in the ammo they are chambered in. A 45 kaboom will be just as exciting as a 9mm kaboom as a 40 kaboom should you not create safe ammo.
 
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