Explain equal SAAMI limits but different ballistics for .357 Mag and 9mm

[rpenmanparker]

I'm posting this in Handloading and Reloading, because I think the folks here are the most knowledgeable about this topic. Upon looking up the SAAMI pressure specs I was shocked (shocked, I say) to learn that .357 Mag and 9mm have the same, exact maximum chamber spec, 35,000 psi. And even more shocking is that 9mm+P is even higher than .357 Mag at 38,500 psi. So why do the normal commercial loading of 9mm and 9mm+P produce such lower muzzle energies than do normal .357 loadings. And even forget normal. Why is it hard to find a 9mm loading that comes close to the mid-range of .357 Mag.

Here is just one example. Two mid-weight bullet loadings, 124 gr Federal Hydra-Shok 9mm at 305 ftXlbf vs. 130 gr Hyrdra-Shok .357 Mag at 572 ftXlbf. The .357 Mag has almost double the energy of the 9mm. Even the 124 gr Federal HST at 355 ftXlbf is anemic compared to the Mag. Those comparisons aren't surprising UNTIL you learn that the two calibers have the same SAAMI maximum cylinder pressures.

I understand that 9mm is a general purpose caliber and there are a wide range of loadings from weak to quite strong available depending upon what you want to do with it. But even the top of the 9mm range and the +Ps don't match up with the middle of the .357 Mag offerings.

Please explain why this is.

 

[MEHavey]

Because the 357 has significantly larger powder capacity -- which means it can burn more powder/dump more total energy into driving the bullet at a relatively-lower pressure.

 

[rpenmanparker]

Because the 357 has significantly larger powder capacity -- which means it can burn more powder/dump more total energy into driving the bullet at a relatively-lower pressure.

Sure, that is obvious. But then why would the less capable 9mm cartridge be awarded so high a SAAMI max. chamber pressure if it is too short to contain the necessary powder to reach the max. pressure? And why would you need a separate +P rating if you can't stuff more powder into the casing anyway?

 

[mjsdwash]

in theory, the .357s having double the case capacity, plus some, and zero margin for setback causing pressure spike, due to not generally using magazines, and being crimped. In practice, most commercial .357 loads are only slightly more than 9mm. 9mm+p+/Nato/Major loads are only about 150fps below typical .357. Be distrustful of published velocity that says otherwise. I have chronod many loads, and most .357 are light. Buffalo Bore is the only one I have chronod that met its claims. Most commercial velocities are from 7-10 inch barrels, or even 16-20.

 

[kcofohio]

As MEHavey and mjsdwash said, case capicity. It gives more room to put slower burning magnum class pistol powder in the case. While the 9mm pressure has peaked and starting its' decline, the magnum pressure is still peaking.

 

[rpenmanparker]

I see that now.

 

[jmorris]

Sure, that is obvious. But then why would the less capable 9mm cartridge be awarded so high a SAAMI max. chamber pressure if it is too short to contain the necessary powder to reach the max. pressure? And why would you need a separate +P rating if you can't stuff more powder into the casing anyway?

You are confusing pressure with velocity. They are not the same and furthermore they don’t even have a linear relationship.

You can plug the bore and have lots of pressure, yet get zero velocity becuse the gun blew apart before the bullet could even exit.

 

[mjsdwash]

Sure, that is obvious. But then why would the less capable 9mm cartridge be awarded so high a SAAMI max. chamber pressure if it is too short to contain the necessary powder to reach the max. pressure? And why would you need a separate +P rating if you can't stuff more powder into the casing anyway?

the .357 uses powder ranging from very slow pistol to very fast rifle powder. Some of the powders it uses are also used in 7.62x39, 30 M1C and 300BO. Using slower burning powders allows more gas for a given pressure, so the pressure remains the same, but the total gas amount is signifigantly increased. This is why a 9mm in a 16" barrel will see around 1-200 FPS increase, while a 357 can easily see a 4-500fps increase. That extra volume really shines in a longer barrel, the same reason why .357 loads are usually tested in them. A 9mm uses fast to slow pistol powders, which are denser. A typical 9mm load fills the case to the bullet base, and will be pushed down when the bullet is put in. You can get a slight increase in velocity from a pressure gain, and it takes only a very small amount of extra powder .2-.5 grains to reach +P levels. Plus P gains are usually not that great, and factory +P is usually hotter due to the greater accuracy of testing in a factory setting allowing a manufacturer to push limits to SAAMI max.

 

[MEHavey]

The 9mm was specifically developed as a smokeless cartridge, whose ballistics could be made "good enough" within the smaller case suitable to an autoloader. (ditto the 45ACP)

But the 357/38 special grew out of the 38 Long Colt, which itself grew of the 38 (short) Colt ... which itself grew out of the converted `51 Navy -- A black powder heritage with large cases -- cases which could put to to good use in revolvers

 

[rpenmanparker]

You are confusing pressure with velocity. They are not the same and furthermore they don’t even have a linear relationship.

You can plug the bore and have lots of pressure, yet get zero velocity becuse the gun blew apart before the bullet could even exit.

Not exactly confusing pressure and velocity, just assuming too much of a correlation. Thanks.

 

[edwardware]

. . . why would the less capable 9mm cartridge be awarded so high a SAAMI max. chamber pressure if it is too short to contain the necessary powder to reach the max. pressure?

1) Max Pressure isn't awarded. It's a design constraint for ammo and firearms.

I think what you're asking is "why have a high max pressure in a short barrel cartridge?" You are (probably unintentionally) assuming that pressure rises for much of the bullet's trip down the bore, so the higher pressure would be wasted in a short bore; this is not so.

2) Max Pressure is generally achieved very early in the bullet's trip; lots of the velocity is gained as pressure is dropping from max. Fast powders drop pressure faster; slow powders, slower. For identical MaxP, a slower powder pushes harder for longer than a fast powder, and achieves higher V, regardless of bore length.

.357 has a larger case volume than 9mm, so you can use a slower powder, which pushes harder, for longer, hence higher V.

 

[LoonWulf]

No replacement for displacement!

I've never gotten to say that.........

 

[Rule3]

I'm posting this in Handloading and Reloading, because I think the folks here are the most knowledgeable about this topic. Upon looking up the SAAMI pressure specs I was shocked (shocked, I say) to learn that .357 Mag and 9mm have the same, exact maximum chamber spec, 35,000 psi. And even more shocking is that 9mm+P is even higher than .357 Mag at 38,500 psi. So why do the normal commercial loading of 9mm and 9mm+P produce such lower muzzle energies than do normal .357 loadings. And even forget normal. Why is it hard to find a 9mm loading that comes close to the mid-range of .357 Mag.

Here is just one example. Two mid-weight bullet loadings, 124 gr Federal Hydra-Shok 9mm at 305 ftXlbf vs. 130 gr Hyrdra-Shok .357 Mag at 572 ftXlbf. The .357 Mag has almost double the energy of the 9mm. Even the 124 gr Federal HST at 355 ftXlbf is anemic compared to the Mag. Those comparisons aren't surprising UNTIL you learn that the two calibers have the same SAAMI maximum cylinder pressures.

I understand that 9mm is a general purpose caliber and there are a wide range of loadings from weak to quite strong available depending upon what you want to do with it. But even the top of the 9mm range and the +Ps don't match up with the middle of the .357 Mag offerings.

Please explain why this is.

What calculator did you use to get those ft lb of energy amounts. You have to take into account the weight of the bullet, weight of the powder and the VELOCITY to calculate ft lbs of energy.

So even though a 124 gr 9mm and a 130 gr 357, are close in weight what are the velocities?

A 40 bullet from a 22 lr yields how much energy? Compared to a 40 grain bullet from a 223/556?? Same weight bullet but a whole lot different

 

[rpenmanparker]

What calculator did you use to get those ft lb of energy amounts. You have to take into account the weight of the bullet, weight of the powder and the VELOCITY to calculate ft lbs of energy.

So even though a 124 gr 9mm and a 130 gr 357, are close in weight what are the velocities?

A 40 bullet from a 22 lr yields how much energy? Compared to a 40 grain bullet from a 223/556?? Same weight bullet but a whole lot different

No, muzzle energy is known just from bullet weight and bullet velocity. Powder weight is part of what generates and also dissipates energy, but the energy of the bullet at the muzzle is defined by the mass of the bullet and how fast it is traveling. The energies are calculated by the standard equation E = 1/2 Mv^2. The energies listed are correct based on Lucky Gunner measurements of the weights and velocities.

 

[Rule3]

No, muzzle energy is known just from bullet weight and bullet velocity. Powder weight is part of what generates and also dissipates energy, but the energy of the bullet at the muzzle is defined by the mass of the bullet and how fast it is traveling. The energies are calculated by the standard equation E = 1/2 Mv^2. The energies listed are correct based on Lucky Gunner measurements of the weights and velocities.

YES but you did not show us any velocities in your OP?
Are the velocities the same??
See post #7
I know how energy is calculated

A SW460 Mag has about the same PSI as a 30-06 rifle. does that make them the same?

 

[rpenmanparker]

YES but you did not show us any velocities in your OP?
Are the velocities the same??
See post #7
I know how energy is calculated

A SW460 Mag has about the same PSI as a 30-06 rifle. does that make them the same?

You are correct. I did not show you any velocities. I showed you the resultant energies. It is understood how velocity would vary to cause those energies. They couldn’t be the same, could they? Easy to calculate velocities, no?

 

[bob_atl]

The central issue here is understanding the integration ( math idea for accumulation) of pressure under the pressure/time curve that forces the projectile out the muzzle.
The fact that SAAMI puts a max pressure on a chamber is not time related.
Muzzle energy is simply based on projectile mass(wt) and projectile velocity at the muzzle.

 

[rpenmanparker]

The central issue here is understanding the integration ( math idea for accumulation) of pressure under the pressure/time curve that forces the projectile out the muzzle.
The fact that SAAMI puts a max pressure on a chamber is not time related.
Muzzle energy is simply based on projectile mass(wt) and projectile velocity at the muzzle.

I get that. Area under the curve!

 

[MEHavey]

And there, my friend, you have literally come to bottom line closure.

 

[Texas10mm]

Go look at SAAMI pressure limit for .327 Federal Magnum.

 

[mavracer]

Velocity isn't related to peak pressure, it's related to pressure under the curve.
Fast powder causes peak pressure with less bullet movement (less volume) once peak pressure is hit pressure drops from there making pressure at the muzzle lower.
Slower powder will cause peak pressure when the bullet further down the barrel (more volume) keeping pressure higher for longer time.
The cavet is it takes more slow powder to reach peak pressure.
H110 is a great powder for hettget max velocity from a 357 but the case is full, using H110 in a 9mm there just isn't enough case volume to get peak pressure resulting in very low velocity.
That's why there's a sweet spot for powders for given applications.

 

[rpenmanparker]

Isn’t it also true that the mass of the bullet makes a difference. For a given pressure (force) the heavier bullet accelerates down the barrel more slowly than the lighter bullet. So overpressuring can occur just due to slow acceleration of the heavy bullet. Hence for a heavy bullet I guess a slower powder would be indicated.

 

[Walkalong]

Have to have room for it as well.

Both are great calibers that do what they do well.

 

[jmorris]

Isn’t it also true that the mass of the bullet makes a difference. For a given pressure (force) the heavier bullet accelerates down the barrel more slowly than the lighter bullet.

Sure mass makes a difference, construction does too. An FMJ will be different than a wax lubed lead bullet.

The softest feeling, in recoil, loads that make power factors in gun games are often fast powders with heavy bullets.

 

[fxvr5]

Here's another comparison to help illustrate the issue of how case capacity influences pressure and velocity.

The 357 magnum has a very long case and overall length and with a pressure limit of 35,000 psi will push a 125 grain bullet to 1450 fps from a 4" (vented i.e. revolver) barrel.

You can get the same ballistics from a semi-auto cartridge, but at a higher pressure because they have less space. For example, the 9X23 Winchester has a much shorter case and overall length. It also pushes a 125 grain bullet to 1450 fps (matching the 357 magnum), though in a 5" barrel. But it's pressure limit is 55,000 psi, much higher than the 357 magnum.

The bottom line is that case capacity matters and determines what type of performance you can produce at a given pressure