Does a bottleneck cartridge increase pressure?

Discussion in 'Ammunition & Reloading' started by dgang, Dec 12, 2018.

  1. jigs-n-fixture

    jigs-n-fixture Well-Known Member Lifetime Supporter

    3,104
    3,769
    113
    You have responded to a lot I didn’t say.

    Guns firing bottle necked cartridges, do typically have longer barrels for the bore, than the same bore with a straight walled case. Yes there are exceptions.

    I didn’t mention expansion ratio, because it wasn’t needed. The statement I did make: that the burn rate is a function of the case volume, bore diameter, sectional density of the bullet and the length of the barrel, covers all of that.

    I try not to get too technical in forum answers. Most folks don’t have enough of a physics, and chemistry background to get very far into the details.

    And I own Brownels “book”, actually a collection of magazine articles, as well as about a dozen others on internal ballistics. Admittedly, most of the books on internal ballistics are more relevant to artillery, because the military has expended far more readership dollars on large arms research than small arms.
     
    Dallas53 likes this.
  2. dgang

    dgang Member

    44
    7
    8
     

  3. dgang

    dgang Member

    44
    7
    8
    I believe that is because commercial loaders use a faster powder because of case size and shorter barrels. If a reloader used the same powder and same weight bullet in each caliber I believe you would see no difference in long barrels.
     
  4. Dallas53

    Dallas53 Well-Known Member Supporter

    16,170
    17,390
    113
    commercial ammo manufacturers use a powder that is optimum for the cartridge being loaded. the powder needed for a 30-30 Win. would be different than a 30-06, or a 300 Win. Mag. all of them are 30 caliber, but require different powders to operate efficiently. they also load ammo based on averages, because guns can be had with different barrel lengths. by reloading, you can tailor and fine-tune your loads to your specific rifle or pistol.
     
  5. JTJ

    JTJ Well-Known Member Supporter

    12,931
    6,773
    113
    Not exactly. Case volume has a lot to do with it. I have considered shortening 38 spl cases to the same volume as the 9x19mm and using 9mm load data for a base line. The main benefit would be in snub nosed revolvers because the fired shells would be easier to extract due to the snubs short extractor rod. 9mm snub revolvers are available so it would just be to make better use of what I already have.
     
  6. JimRau

    JimRau Well-Known Member Supporter

    7,204
    3,274
    113
    In a word YES!!!;)
     
    JTJ likes this.
  7. jigs-n-fixture

    jigs-n-fixture Well-Known Member Lifetime Supporter

    3,104
    3,769
    113
    No, bottle nick cartridges do not increase pressure. Bottle neck cartridge loads are designed to be loaded, and function at higher pressures. Thus the loads designed for them are based on higher pressures.

    A given quantity of of a given powder, produces a predictable volume of gas when it is ignited. The pressure it develops is proportional to the case volume, and the pressure is the same in all directions. The case configuration is not a factor in that pressure production.
     
    Dallas53 likes this.
  8. JimRau

    JimRau Well-Known Member Supporter

    7,204
    3,274
    113
    Can you say 'expansion ratio' and still say that bottle neck cartridge do not increase pressure. Also just check the burning rate of the powders in straight wall cartridges compared to bottle neck cases.;)
     
  9. jigs-n-fixture

    jigs-n-fixture Well-Known Member Lifetime Supporter

    3,104
    3,769
    113
    38-SPCL has a SAAMI Pressure rating of 17-kpsi, with “plus p” loads of around 20-kpsi. It was invented around black powder, and had low pressures from the start.

    The 9x19, was developed just a few years later, but was designed from the ground up, as a smokeless powder round. The standard pressure is 35-kpsi, with “plus p” rounds around 38-kpsi.

    The higher pressure has everything to do with the powder selection, and nothing to do with the case volume.

    I’m seeing a lot of opinions being posted that are indicative of a total lack of a working knowledge of the physics and chemistry involved. Most of them are just plain wrong. Some of them are dangerously wrong.

    This is reminding me of something my Dad told me about engineering when I was a kid: given enough time, enough resources, and enough failures, any damned fool can build a bridge to take a tractor with a bale trailer across a creek. If you need it done in a timely manner, with limited resources, and capable of carrying a given maximum load repeatably, you better higher an Engineer, who actually understands what the hell he’s doing.
     
    Dallas53 likes this.
  10. JTJ

    JTJ Well-Known Member Supporter

    12,931
    6,773
    113
    I should have noted my revolvers are 357 magnum not 38 spl and capable of handling the higher pressure. The reason that round is not commercially available is it would fit in a 38 spl that is not able to handle the pressure.
     
  11. dgang

    dgang Member

    44
    7
    8
     
  12. dgang

    dgang Member

    44
    7
    8
    I agree. Should have said a little difference because of the different case lengths, and resulting pressure.