The Down Range Forum
Member Section => Down Range Cafe => Topic started by: Paraguy on December 04, 2010, 02:57:58 PM
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I am puzzled, why is it that a 38 Special +P and a 9mm +P round look identifal in all ways except that the .38 looks to be about 50% longer. Even more puzzling, even though it is has about the same weight projectile and the room to hold about 50% more gun powder it delivers it at about 150fps slower than the 9mm. Is there a logical explanation why one round is slower than the other (all things being equal such as brand, weight, both rated +P etc. ?)
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Hmmm. Great question. Is it because of the slight gap @ the cylinder releasing some pressure? Or is it the type of powder used? Or something totally different? Beuhler?
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Hmmm. Great question. Is it because of the slight gap @ the cylinder releasing some pressure? Or is it the type of powder used? Or something totally different? Beuhler?
Just wanted to show I'm curious as well.
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Originally, the .38 Special replaced the .38 Long Colt and was a black powder cartridge. Case length probably was driven by those factors. Black powder can be loaded by volume rather than weight.
Old rounds developed for different firearms at about the same time. We didn't adopt the 9mm in the West for some time so the .38 was the "Cartridge de jour!".
Just a wild guess...
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+P for the .38 is less pressure than +P in a 9mm. 20,000 vs. 38,500 PSI.
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Originally, the .38 Special replaced the .38 Long Colt and was a black powder cartridge. Case length probably was driven by those factors.
Ya, agreed on that. But given the extra case length and powder advances, one would figure the velocities would be higher for a larger volume of powder.
This is a good discussion.
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True but modern powders are not loaded by volume. They're loaded by weight and and that's determined by case pressures that you'd rather not exceed for a particular firearm. Luger, when he developed the cartridge in 1901 obviously loaded it and designed the firearm for it at exceedingly higher pressures and velocity but not at +P pressures.
In 1902, the .38 needed a better powder but it was being used in older frames. It's size is based on that history, not the pressures of modern frames. A 100 year old .38 special can't be loaded with +P cartridges any more than a 100 year old Luger can handle a +P cartridge. Remember, regardless of how many grains required, you may not be coming anywhere near completely loading the case with powder.
I'm not a loader, that's the guy that's should have some knowledge. I'm still just guessing..
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In this specific case, both are Golden Sabres, rated +P and one is 124 grains the other 125, yet the velocity is 150 fps different in favor of the shorter 9mm.
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In this specific case, both are Golden Sabres, rated +P and one is 124 grains the other 125, yet the velocity is 150 fps different in favor of the shorter 9mm.
But the powder "grain" weight behind the bullet is much lower in the .38 cartridge regardless of the size of the case. The 9mm Luger is loaded with more powder by weight.
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+P for the .38 is less pressure than +P in a 9mm. 20,000 vs. 38,500 PSI.
Pressure is what drives the bullet. The more pressure the faster the bullet speed. The actual weight of the powder means little. It's the pressure that powder produces that causes bullet movement. If you check you'll find there is less room for powder in the 9 case than in the 38 case. Each of these cartridges are designed for a given maximum pressure. This is not exceeded by the factories.
Also understand that the closed breach of the typical 9 mm handgun allows all the propellent gases ( pressure) to propel the bullet none of this gas is lost in a barrel/cylinder gap. All of this comes into play as the limiting factures of velocity.
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I think Tim has it right, the 38 was originally a black powder cartridge, while the 9MM was designed for smokeless powder.
I don't have a pistol reloading manual to check, but 1 grain difference in weight says they are essential the same bullet, in that situation case volume is irrelevant, what matters is the pressure range that it was designed for.
I would bet that if you pulled bullets and weighed the powder charges, assuming they are the same powder, the 38 will have a lighter charge. The reason the case is longer on a 357 mag than on a 38 is for safety, the Magnum load will easily fit in the 38 case,
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AND a .357 Mag load will leave ALL 9mm rounds in the dust, hands down.....it's why we have the .357 Sig. Look at the numbers behind that round. They're pretty impressive but a different geometric configuration being basically a 10mm case dia necked down to a use a .355 dia bullet.
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The higher-pressure .38 +P loads at 20,000 PSI offer about 20% more muzzle energy than standard-pressure loads and places between .380 ACP and 9 mm Parabellum, similar to that of 9x18mm Makarov.
38 S&W Special
Bullet weight: 158 gr
Muzzle velocity: 940 ft/s
Muzzle energy: 310 ft•lbf
Max pressure: 17,000 PSI
.38 S&W Special +P
Bullet weight: 158 gr
Muzzle velocity: 1,000 ft/s
Muzzle energy: 351 ft•lbf
Max pressure: 20,000 PSI
.380 ACP
Bullet weight: 100 gr
Muzzle velocity: 895 ft/s
Muzzle energy: 178 ft•lbf
Max pressure: 21,500 PSI
9x19mm Parabellum
Bullet weight: 115 gr
Muzzle velocity: 1,300 ft/s
Muzzle energy: 420 ft•lbf
Max pressure: 39,200 PSI
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The question is being danced around quite nicely, ammo makers have to defer to the lowest common denominator, the firearm itself, every cartridge built has to be able be shot in the weakest firearm chambered for it. As the .38spl was originally a black powder cartridge, new ammo must be safe in that firearm. +p states on the box safe only in firearms rated for +p, but is not hot enough to blow a pistol up, but stress it a lot. The 9mm was built around more modern firearms able to take the 35k psi pressure. Believe me, .38 can be loaded a lot hotter, but should only be used in .357 mag cylinders. I load .38 short colt with 130grn fmj at 1000 fps, for a particular game for a particular reason. I have also loaded .38spl with 158grn bullets at 1150 fps, and have shot over 100,000 of these through 2 L frame S&W revolvers, loads will not be given. Also look at the cross section of the cases, the 9mm has a thicker web at the base than the .38spl.
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Thanks M25
Knew we could count on you for the accurate answer.
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Pressure is what drives the bullet. The more pressure the faster the bullet speed. The actual weight of the powder means little. It's the pressure that powder produces that causes bullet movement. If you check you'll find there is less room for powder in the 9 case than in the 38 case. Each of these cartridges are designed for a given maximum pressure. This is not exceeded by the factories.
Also understand that the closed breach of the typical 9 mm handgun allows all the propellent gases ( pressure) to propel the bullet none of this gas is lost in a barrel/cylinder gap. All of this comes into play as the limiting factures of velocity.
I think we have a winner. All things being equal, a revolver will allow some gas to escape where as a pistol won't. I could be wrong here, but this seems the most likely culprit as its the one constant difference. Any science guys out there?
FQ13
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Thanks to all, this has been quite an education!
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The question is being danced around quite nicely, ammo makers have to defer to the lowest common denominator, the firearm itself, every cartridge built has to be able be shot in the weakest firearm chambered for it.
Exactly right.
Same reason the 270 Win, 280 Rem, etc. is loaded to higher pressure than 3006.
Same case, same web but there are no 1903's in 270 Win.
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All makes sense, a Chevy 350 Cu. in engine has between 140 and 1,000 horsepower depending on what is on the inside, but it is the same size onn the outside regardless.