Why does a 9mm have so much power in a small cartridge?

Why does a 9mm have so much power in a small cartridge?

This is a discussion on Why does a 9mm have so much power in a small cartridge? within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; 38 special has a brass that is twice the size of 9mm brass. Pretty comparable bullet weights but the 9mm travels a couple hundred FPS ...

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Thread: Why does a 9mm have so much power in a small cartridge?

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    New Member Array Darktone's Avatar
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    Why does a 9mm have so much power in a small cartridge?

    38 special has a brass that is twice the size of 9mm brass. Pretty comparable bullet weights but the 9mm travels a couple hundred FPS quicker. I am guessing it’s the powder type?

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    Max pressure rating.

    38 SPCL +P is 20,000 PSI, while the 9mm is 35,000 PSI (+P is 38,000-ish?)
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    VIP Member Array Havok's Avatar
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    Just depends on the ammo manufacturers you're comparing.
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    The both work & fail at times. se the most , as best as you can.
    Me I like my 9mm with 13 rounds +p, of course ; )
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    VIP Member Array Chuck808's Avatar
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    38spl was originally derived as a black powder cartridge. Because black powder has a much lower yield, you needed a much larger case to get a usable velocity. Now that we use it with smokeless powder, you get much lower pressure in the case, due to its large size. In some of the hot 357 Magnum loads, like a 125gr jacketed bullet over a max charge of H110, which the Lee manual states is a 22.0gr charge, the case is so full that youíre actually compressing the powder in the case. With that load, youíre seeing pressures of 41,400 CUP. Compare that to something like a 38spl with a 125gr cast bullet. Hodgdon claims a 2.5gr charge of Clays is the minimum load, giving 8,400 CUP of pressure. That is much more in line with the type of pressure you would see with a black powder load, but because youíre using smokeless powder, the 2.5gr of Clays would just be a tiny little charge that probably only takes up 25% of the rest of the case capacity. It would be so low in capacity, I bet many reloaders would opt to put a bit of cotton over the powder to keep an excessive airspace out of the cartridge, and ensuring a better burn of the powder.

    9mm has always been a smokeless powder cartridge, and with smokeless powder being much more energy dense than black powder, you can use a much smaller case to get a usable velocity, and in this case, enough pressure to cycle the action of a semi-auto handgun, as it is most typically used in.

    In the rifle realm, you could say 45-70 Govt vs 458 Socom is an analogous situation.Both are big bore rifle rounds that shoot 0.458Ē diameter projectiles. The 45-70 was a black powder cartridge, and is huge because of it. The 458 Socom is a smokeless powder load, and with a much shorter case (40mm bs 53.5mm) you can get an equal gullet weight to the same velocity, although the 458 Socom achieves a higher pressure.

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    VIP Member Array LimaCharlie's Avatar
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    Go a silly millimeter larger and see the power.
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    VIP Member Array flintlock62's Avatar
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    Quote Originally Posted by LimaCharlie View Post
    Go a silly millimeter larger and see the power.
    I like 11.43 mm
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    38spl was originally derived as a black powder cartridge. Because black powder has a much lower yield, you needed a much larger case to get a usable velocity.
    True
    Max pressure rating.
    38 SPCL +P is 20,000 PSI, while the 9mm is 35,000 PSI
    Also True

    But there's something really interesting about 38 vs 9mm I had to add.
    Not only is it not a more powerful powder, you can actually use less of the exact same powder to make higher performance in 9mm. The smaller case size causes higher pressures. More efficient use of expanding gasses.
    According to my Lyman's 49th Edition Handbook. All from a 4" test barrel.
    9mm: 125gr JHP with Unique 5.0 grains = 1078 FPS @ 30,700 PSI
    38 Special: 125gr JHP with Unique 6.0 grains = 895 FPS @ 16,700 PSI
    And for a comparison
    .357 Magnum: 125gr. JHP with Unique 7.0 grains = 990 FPS @ 18,900 PSI
    .357 Magnum: 125gr. JHP with Unique 9.7 grains = 1359 FPS @ 41,600 PSI
    msgt/ret, Chuck808, OD* and 8 others like this.

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    VIP Member Array OldChap's Avatar
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    The difference is there are a lot of differences.

    Begin with the cartridge itself. Designed to hold the chamber pressures of the day, .38 Special was designed in a day (1898) when powders could not generate the pressures we see today. Then there is the physics issue @SunTsu points out. A smaller, stronger case develops higher performance than a large, lightly constructed case, given the same powder charge. Chalk that one up to chemistry.

    Then consider mechanical design and construction of the weapon. Modern 38 Specials may be designed to contain more pressure than early designs ever were, but ammunition manufacturers must anticipate that at some point a load which develops very high chamber pressure might be loaded in an old gun. The results could be catastrophic. So all loads, and recommendations in reloading manuals, must be kept to the lower standards for safety. Chalk that one up to metallurgy.

    Then consider bullet construction. When the 38 was designed, most guns used lead bullets that were cast with "soft" lead. Hard cast techniques only came along later. Pushing a soft lead bullet at high velocity quickly "leads" the barrel and destroys accuracy at the least, and increases chamber pressure at worst. The 9mm was originally designed to use a plated bullet, which could handle higher velocities without problems.
    Last edited by OldChap; May 22nd, 2020 at 01:04 PM.
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    VIP Member Array SatCong's Avatar
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    Quote Originally Posted by LimaCharlie View Post
    Go a silly millimeter larger and see the power.
    Maybe 10mm!
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    Quote Originally Posted by SatCong View Post
    Maybe 10mm!
    Yep, 25 years of the 10mm being my principal carry handgun. That one silly millimeter, who'd of thunk...
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    So the 38 cartridge is only partially filled with powder because it can’t handle the pressure of being filled with modern powder.
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    VIP Member Array LimaCharlie's Avatar
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    Quote Originally Posted by Darktone View Post
    So the 38 cartridge is only partially filled with powder because it canít handle the pressure of being filled with modern powder.
    Kind of like a .45-70.
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    VIP Member Array OldChap's Avatar
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    Quote Originally Posted by Darktone View Post
    So the 38 cartridge is only partially filled with powder because it canít handle the pressure of being filled with modern powder.
    Correct. A careful reloader can push a .38 Special a good deal beyond what it was designed to handle, provided he examines the spent casings for signs of excess pressure, and uses a modern gun in good condition. Not just any gun, but one known to be able to handle high pressures. I won't name any here for obvious reasons. Of course, every manufacturer will automatically void your warranty if you do that.
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    Senior Member Array SmoothJazz's Avatar
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    Were there any other pre-WWI handgun cartridges that operated at 9mm Para pressures ? Or was the 9mm one of those designs that was that far ahead of its time?
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