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Short barrel velocity loss?

Discussion in 'General Firearms Forum' started by Metal Angel, Mar 20, 2012.

  1. Metal Angel

    Metal Angel

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    How much velocity do you really lose out of a short barrel? Is there some kind of formula? And what do you gain in a pistol caliber carbine? A couple hundred fps? 300? 400? If you only gain a few hundred feet per second when you add 13 inches of barrel, how much will you really lose when you subtract an inch or two? Maybe there is no need to worry about velocity loss in short barrel pistols... Anyone have real numbers? Or any knowledge of the subject?
     
  2. AA#5

    AA#5

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    I have chronographed numbers from an AA Loading manual that has velocities for pistol-caliber carbines.

    For higher-pressure calibers like 9mm in 16-in. barrels, you can figure about 100-150 fps increase. For lower pressure calibers like 45 ACP, there is usually very little or no velocity increase.

    For std. caliber handgun calibers, it depends on whether the powder is slow or fast burning. Generally, you lose about 20-50 fps for every inch shorter barrel; more for magnum calibers with slower powders.
     
    Last edited: Mar 20, 2012

  3. 4 glocks

    4 glocks

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    The #'s I have seen in 9mm is about 200 FPS depends on the loading.
     
  4. chemcmndr

    chemcmndr

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    PM me and I can e-mail you an excel file I have where I've chronographed 9mm from the Glock 26 to a 10.5" AR and .223/5.56 from 11.5" to 20" ARs.
     
  5. chemcmndr

    chemcmndr

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  6. DonD

    DonD

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    Generally speaking the higher the pressure the cartridge and the higher the intensity (being "overbore", lots of powder for a specific bore diameter) the higher the loss per inch of barrel. Don
     
  7. BFN

    BFN

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    "Ballistics by the Inch" will answer a lot of your questions http://www.ballisticsbytheinch.com/calibers.html

    Some observations: The largest velocity increases are at the first couple of inches of barrels. There is a "law of diminishing returns" with each additional inch the increase is less, until drag takes over and a longer barrel will reduce velocity - this happens at 12-16" for 45 ACP 230 gr. Rifle cartridges can go over 30" before they lose velocity.

    I use at least 3" barrel for 357 mag. With a 2", there is too much velocity loss.

    For 45 ACP, I use at least 4"

    For 38 sp, I use 2.5". This is 33% more than 1.875", it doesn't sound like much, but is 33% longer and has been proven to add another 100 FPS for the 38 sp, which needs all the help it can get.
     
  8. BFN

    BFN

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    One more thing I will add - each barrel is different, there will be some variance within same barrel lengths because of chamber tightness etc. This is especially true of revolvers because of cylinder to barrel gap and other reasons, so a 6" revolver barrel may not be faster than a 4". But a 3" always seems faster than a 2", as a lot of unburned powder is left on the 2" when the bullet leaves the barrel (just try shooting a 357 snubbie at night!)
     
  9. iceburg

    iceburg

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  10. cowboy1964

    cowboy1964

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    Ballisticsbytheinch is a great site with real, hard, numbers.

    For me I consider 3" for 9mm to be my absolute minimum and then only in a pocket pistol. 4-4.5" is the ideal. In .45 I wouldn't go less than 4" unless I really had to.
     
    Last edited: Mar 20, 2012
  11. cowboy1964

    cowboy1964

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    Use Gold Dot 135+P Short Barrel ammo. For me the only reason to use a .38 snub is for the size advantage.
     
  12. barth

    barth six barrels

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    Formulas are just estimates and can be good to ridiculous.
    Even test barrels are just that - test.
    Particular guns have different chambers.
    Various ammo, particularly with new fast burn low flash powder,
    can have different results with velocity coming from the same gun.

    I like to find folks that have chronographed real and specific ammo, from real guns, to determine actual velocity of a given round and weapon.
    Usually internet searches can come across such data.

    Particularly on common guns and SD ammo combinations.
     
    Last edited: Mar 20, 2012
  13. BFN

    BFN

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    Thats the cartridge I use, but it will be faster with a 2.5 compared to a 1.875. I find my 2.5" barrel S&W 642 easy to hide in a pocket.

    Here is a review for a 1.875 vs 2.5" for M638. Note that the 2.5" actually had a larger B/C gap, but still got up to 100 FPS more velocity.

    The 135gr +P has been proven effective in 1.875" standard snubbie length. I just believe that I will get a slight edge with a longer barrel, along with slightly better accuracy and less recoil.
     
  14. BFN

    BFN

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  15. powder86

    powder86 SHOOT SAFE!

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    for those saying a minimum of 4" for 45acp... what are your thoughts on g30? with a 3.8" barrel, should i then carry +p ammo to get necessary velocity for penetration and proper expansion? i read somewhere that you need minimum 750 ft/s, to get expansion for a 45acp hp.
     
  16. BFN

    BFN

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    My own preference of "4 inch minimum" is not meant to be exact, I have owned a G36 with a 3.78 barrel and that is close enough. I would not want a 45ACP in the 3-3.5" range. I currently use Win Ranger T 230gr +p, but I also believe regular velocity 45 ACP is effective at around 4" (which includes 3.8"). They claim modern 45ACP will expand at 700+ FPS, but I would rather have 850+ for the cold, wet Northwest weather and heavy clothing. Cold temperatures also reduce velocity.

    At the other end, 45 ACP does not gain meaningful velocity with more than a 5" barrel. I also have a 6" longslide, but it is mainly for target.