Does less barrel length = less accuracy due to the shooter, or the barrel? (pistol length)

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  • teratos

    My hair is amazing
    MDS Supporter
    Jan 22, 2009
    46,989
    Bel Air
    I’m Irish. Very low pressure in the chamber. 2 kids, first month of trying, both times.
     

    smokey0118

    2A TEACHER
    Jan 31, 2008
    28,398
    It has been said that the way to define horsepower Vs. Torque is...

    HP is how hard you hit the rock wall.
    Tq is how deep you go into the rock wall.

    The point in the RPM where most engines produce the same numbers in tq and hp... (where the lines cross on the graph) is around 5225 rpm.

    That aside...
    With respect to the topic of barrel length...


    https://gunmagwarehouse.com/blog/does-barrel-length-affect-bullet-performance/
    states...



    Cool, they're also wrong. Pressure spikes early in ignition to its peak and then rapidly falls. The bullet moving down the bore increases the volume of the cylinder behind the bullet containing the pressure. This(and the rate of converting powder to gas) means pressure spikes early on and then rapidly falls. Pressure does not "build" in longer barrels.

    As stated before, pressure spikes early and then falls. It takes a while for pressure to fall to a low enough differential from the pressure in front of the bullet for acceleration to slow to zero. Longer barrels produce more velocity because this acceleration due to the pressure differential acts on the projectile for a longer duration, even though acceleration is reduced the further down the barrel the projectile goes.


    Screenshot_20220515-190557_Gallery.jpg
     
    Last edited:

    Pinecone

    Active Member
    Feb 4, 2013
    27,846
    Cool, they're also wrong. Pressure spikes early in ignition to its peak and then rapidly falls. The bullet moving down the bore increases the volume of the cylinder behind the bullet containing the pressure. This(and the rate of converting powder to gas) means pressure spikes early on and then rapidly falls. Pressure does not "build" in longer barrels.

    As stated before, pressure spikes early and then falls. It takes a while for pressure to fall to a low enough differential from the pressure in front of the bullet for acceleration to slow to zero. Longer barrels produce more velocity because this acceleration due to the pressure differential acts on the projectile for a longer duration, even though acceleration is reduced the further down the barrel the projectile goes.


    View attachment 366457

    Don't confuse RD with facts. He will go crazy trying to back pedal and claim he did not say what he said.

    And RD, the DEFINITION of HP is HP = Torque x (RPM/5225)

    So the point where the HP and torque are equal numbers is EXACTLY 5225 RPM.
     

    Bohemian

    Junior Member
    Nov 7, 2009
    60
    I know a longer barrel improves accuracy, but is there more to it (as in bullet stabilization) than just the ability of the shooter to deal with barrel length? Some people can shoot a snubbie with accuracy, while most probably cannot. Does the longer barrel, at handgun length, improve accuracy even for those who can shoot a snubbie accurately?

    here's a visual for you, at 25 feet at a indoor range I could see the .45 Long Colts tumbling before they hit the paper target when fired from my bond arms derringer. This was further supported by diagonal projectile punches in the target. The same was not true for the same .45 long colt ammo fired from my 4-3/4" Colt SAA Revolvers. The hole punches were round and perfect and I could not see the round at all when fired.
    So in a nut shell shorter barrels do not give much time for powder to burn, and slow the velocity down, and there's less twist/rifling in a shorter barrel which impacts projectile stability and accuracy. The inverse is true for longer barrels.

    That being said derringers and snubbies are great for up close and personal, like less than 10 feet, like in your house or if someone bum rushes you in a parking lot, etc.

    Size matters, I would not carry anything for self defense smaller than a .380 acp aka 9mm short. Anything smaller than that is a nose gun, great if you're grappling with someone and you can't get to anything else.

    In the home my preference is revolvers and 12 gauge pump shorty's. Revolvers never have a failure to feed like anything with a magazine can. Once less failure point when subseconds count.

    I have a S&W .357 Magnum 686 snubbie on the nightstand and a Mossberg 12 Gauge Shockwave next to that.
     

    Mark75H

    HVAC Expert
    Industry Partner
    MDS Supporter
    Sep 25, 2011
    14,527
    Outside the Gates
    Revolvers can fail several ways, fail to rotate/lock up, fail to draw hammer back, fail to release hammer, hammer fail to contact primer. On well made guns these failures are rare, but not impossible.
     

    teratos

    My hair is amazing
    MDS Supporter
    Jan 22, 2009
    46,989
    Bel Air
    well like a fish who does it in the water and the female swims through it?
    :lol:

    More like throwing a hotdog down a hallway (no offense to my better half) and hitting a bullseye everytime. I’m like one of those long range rimfire shooters.
     

    lazarus

    Active Member
    Jun 23, 2015
    8,752
    I think he's referring to peak pressure, which happens very early on in internal ballistics. Velocity is a result of a pressure differential accelerating the projectile for a longer duration. Peak pressure isn't higher in a longer barrel.

    That unburned powder you mention is one of the reasons I mentioned that longer barrels can have more consistent powder burn(and therfore velocity) in comparison to a shorter barrel.
    He is.

    Roaddawg, look at a pressure curve chart. The peak is within a few hundred micro seconds. Basically right after the bullet separates from the casing and begins to be accelerated down the barrel. If you get short enough, yes peak pressure will be low enough. But you'd need to be in the realm of a barrel +/- about the length of the bullet past the throat. So most guns you are talking between half an inch to an inch and a half (as you measure a revolve. Semis are measured from the bolt/slide face, so the COAL+ .5-1.5").

    Longer than that and the pressure is dropping.

    Yes, you have unburned powder. Longer barrels allow that powder to completely burn, but the bullet is traveling down the barrel and increasing the combustion chamber volume faster than pressure can build from powder combusting. Same reason peak pressure in an engine combustion chamber is achieved milliseconds after ignition even though the gas doesn't really fully burn immediately. The rising piston increases chamber volume faster than combusting air and fuel can increase pressure.

    The longer barrel allows the pressure to act for longer, as well as more time for a slower burning powder to KEEP the pressures higher than a fast burning powder would. Within reason, you'd achieve maximum energy imparted to a bullet if you could combust all of the powder instantly. You'd also explode any gun. Compare a rifle and handgun. Most rifles have both more powder and more powder fill than a handgun. With a few exceptions, you do NOT do 100%+ powder filles on a handgun with a pistol powder. That's a bomb in your hand. Rifles frequently use powders that call for compressing the loads because they have >100% fills. This is because they powder burns slower. If you used a pistol powder in a rifle case, filled it to say, 105% compressed charge and set it off, you might have 140, 150, 160k PSI of pressure generated. If the combustion chamber COULD contain that, you'd have significantly more energy in the bullet.

    But since you can, you reduce the burn rate of the powder to keep peak pressure at what the case and chamber can handle and allow it to continue combusting as the bullet travels down the barrel. The continued combustion keeps pressures higher so there is less drop off in pressures. That pistol powder, if it has the same energy, would generate maybe 150k PSI at ignition and maybe 10k PSI as the bullet uncorks from a 20" barrel. A slow burning rifle powder might only hit 50k PSI peak, but also still have 10k PSI when it uncorks. So significantly less energy imparted in to the bullet. But because everything is going to blow up if you try that, you'd have to reduce how much powder you use that is fast burning to reduce the peak pressure to 50k PSI. Well NOW, that pistol powder is generating the same max peak pressure, but it might only be generating 3500PSI when the bullet uncorks. So the imparted energy is significantly lower (you integrate below the pressure curve, multiply by the bullet base diameter and reduce by the friction of the bullet traveling down the barrel and there is your imparted energy. Simplified of course).

    A Bullet is going to have more energy the longer the barrel is up until the point that the friction of the bullet traveling down the barrel exceeds the force of the pressure behind the bullet. There is no realistic barrel length where this will be true for 99.9% of cartridges. An exception is a 22lr, which has very low pressures and a very small initial combustion chamber. Most standard velocity and subsonic leads generate peak velocity/energy out of between a 14-18 inch barrel and will begin dropping after that point.

    You could probably contrive some other situation where that would be true, like maybe a 30" barreled .45acp or 32acp or something else very low pressure.

    A revolver and semi-auto will not generate the same peak pressures because of the revolvers cylinder gap. The barrel length has nothing to do with it. A 2.5" 9mm will generate the same peak pressure as a 6" 9mm.

    Changing powder types will shift when that peak pressure occurs though, even if it is still microseconds after combustion begins. But it might be as the bullet is 1.2" down the barrel versus .6" down the barrel for fast pistol powders.
     

    Mark75H

    HVAC Expert
    Industry Partner
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    Sep 25, 2011
    14,527
    Outside the Gates
    The rising piston increases chamber volume faster than combusting air and fuel can increase pressure.
    Since we are nitpicking, rising piston DECREASES chamber volume. Pretty sure that was just a typo, but internal combustion engines are a lot different - and Diesels and gas engines are different from each other. Would have been better just to leave them out as a comparison.
     

    lazarus

    Active Member
    Jun 23, 2015
    8,752
    Since we are nitpicking, rising piston DECREASES chamber volume. Pretty sure that was just a typo, but internal combustion engines are a lot different - and Diesels and gas engines are different from each other. Would have been better just to leave them out as a comparison.
    Yup typo. I meant decreasing.

    Not different in that they all obey the ideal gas law and thermodynamics.
     

    Mark75H

    HVAC Expert
    Industry Partner
    MDS Supporter
    Sep 25, 2011
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    Outside the Gates
    They are the same in desiring peak cylinder pressure at optimum crank angle, but they differ in when begins ignition and flame rate.
     

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