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How does shoulder angle affect cartridge performance?

Discussion in 'Handloading and Reloading' started by Uncle Richard, Nov 25, 2012.

  1. Uncle Richard

    Uncle Richard Well-Known Member

    How do different shoulder angles affect cartridges? Specifically, how would the performance of a cartridge vary if it had a small shoulder slope of 10deg compared to steeper slope of 60deg, keeping all other dimensions relatively the same?
  2. Plain Old Bill

    Plain Old Bill Well-Known Member

    Ok, the correct answer to that question for me is "I don't know." BUT- if I were going to research it, I'd take a look at the wildcats that were formed by a differing shoulder angle from standard calibers. I know that .30-06, .25-06 and .270s have had their shoulders angled up or down from standard, but would have to do some research to see what they were called, and then how similar loadings in the standard calibers did as opposed to the wildcat. I'd be a bit suspicious of the wildcat info as no one likes to admit they just went to a great deal of expense and time to create a wildcat caliber that requires special dies, specially formed brass, and lots of money without appreciable differences in results.
  3. Fatelvis

    Fatelvis Well-Known Member

    Just an obvious observation of mine, and I'm by no means an expert:
    It seems that the higher pressure/performance cartridges have sharper/ more defined shoulders. "Milder" cartridges such as 22 Hornet, 22 Jet and such, seem to have shallower angled shoulders. Of course there will be exceptions, but I think the shallow shoulder is seen to "waste" cartridge capacity, and I think that is why when a cartridge is "improved", the shoulder is almost always blown out to some degree. The Weatherby series throws us a real curveball with it's radiused shoulders! I'm interested to see if anyone (of knowledge) can chime in and explain!
  4. rcmodel

    rcmodel Member in memoriam

    There is no evidence to support anyones claim that a steep shoulder angle, or Weatherby's double radius venturi has any effect at all on performance.

    What the steeper shoulder angles do is increase powder capacity of the case, which in turn can give higher velocity.

    It also prolongs the life of the brass because the steep shoulder helps prevent as much case stretching.

  5. Swampman

    Swampman Old Fart

    +1 for what rcmodel said, it's not the steep shoulder that increases velocity in Ackley Improved cartridges, it's the increased case capacity.
    While steep shouldered rounds decrease case stretching, they also do a good job at hiding some excess pressure signs.
    Be careful.
  6. Slamfire

    Slamfire Well-Known Member

    Some shoulder is important. I have a 35 Whelen and the cartridge has very little shoulder. As such I am of the opinion that the slight shoulder contributed to the misfires and hangfires I had in that rifle. I think a slight shoulder cushions the firing pin blow.

    Guys have run tests on case capacity, that has a more important effect on pressures and velocities than shoulder angle.

    How much taper a cartridge case has is very important. Straight cases don't feed well, don't steer well, and don't come off the chamber walls well.
  7. KevinR

    KevinR Well-Known Member

    The straighter the case is from base to mouth the better the transfer of pressure.
  8. rcmodel

    rcmodel Member in memoriam

    Can you document that?

    If you can, that would be something I have never seen in print anywhere else.

    And if it were true, HV tank & artillery shells would be 6 foot long and straight sided, but they are not..

  9. kelbro

    kelbro Well-Known Member

    I have read that the Ackleyized cartridges are also easier on throats. Not sure how to confirm or quantify that. maybe it was just empirical results that someone noticed.
  10. Uncle Richard

    Uncle Richard Well-Known Member

    2nd rcmodel....

    Actually, you will get a better and more efficient use of pressure with a non-straighted walled case. The smaller diameter neck creates a higher pressure and faster velocity pushing the bullet out. As diameter decreases, velocity and flow increases.
  11. Kachok

    Kachok Well-Known Member

    The shoulder makes a focus point of the hot gasses beyond which there is an eddy flow that moves faster then the gasses at any other point of the system. These faster moving gasses/unburnt powder create more errosion via heat and abrasion, so using a sharper shoulder absorbes more of that abrasive energy on the neck of the cartrage rather then the throat because the eddy flow is moved reaward. Sharper neck angles seem to help accuracy as well, much debate has gone into this but the fact remains that nearly every top level long ranged rifle in the past two decades has had that cartrage design. 6.5-284, 280AI, 7mm WSM, and 300 WSM most noteably, they all have 35 degree or sharper shoulders.
  12. J-Bar

    J-Bar Well-Known Member


    For a case that headspaces on the shoulder, would not a sharp shoulder give more precise headspacing?

    Second speculation/question:

    Are not the old British cartridges for dangerous African and Indian game gently tapered to ensure easier extraction of the fired cartridge? I mean the last thing you want when you are facing an animal that can kill you is a case stuck in the chamber!
  13. rcmodel

    rcmodel Member in memoriam

    The old British cartridges were tapered because they were first loaded with stick cordite powder.
    Which closely resembles uncooked spaghetti.


    The only way they could get it in the case was by using the slight taper of the .300 & .375 H&H.
    That or put the cordite in the case and then form the shoulder later like they did on the .303 British.

    That is also why they first used a belted case to headspace from.
    Because there was no shoulder, and unlike the 303, and they were rimless cases..

    A side benefit was the slickest feeding of any cartridge design since, & easy extraction.

  14. J-Bar

    J-Bar Well-Known Member



  15. Uncle Richard

    Uncle Richard Well-Known Member

    "eddy flow"......reminds me of my college days studying chemical engineering
  16. wv109323

    wv109323 Well-Known Member

    Another twist on the shoulder angle is that the benchrest cartridges of .22 PPC and 6mm PPC both had sharp shoulder angles. These were designed for maximum accuracy.
    A disadvantage to the sharp shoulder angle is that it is more difficult to feed through auto loading actions. Most sharp angle cartridge rifles are bolt action.
  17. rcmodel

    rcmodel Member in memoriam

    I think I knew Eddy Flow.
    He hung around with Arther Ritis didn't he?

    Never did like either one of them punks.

  18. Uncle Richard

    Uncle Richard Well-Known Member

    Never met those guys.... thankfully I’m still young.
  19. fguffey

    fguffey Well-Known Member


    Eddy: Eddies are found behind rocks in a stream, the rock causes a vacuum behind the rock, water passes on both sides of the rock and after passing curl back, so, I would say the reduced diameter of the neck is more like a venturi.


    Reducing case taper increases powder capacity, the long tapered case was necessary in the old days when forming cases, the sharp shoulder of wildcats complicate the manufacturing of ammo and there is the stretch and flow, or is that stretch and or flow, then there are do-nuts, I create do-nuts, I make do-nuts, when forming 30/06 cases to 6MM Remington expect do-nuts, when forming 6MM Remington to 22 Remington Ackley improved wildcat something or the other I make do-nuts, if it was not for the sharp shoulder I would not expect do-donuts, thick necks? Yes, but not do-nuts.

    F. Guffey
  20. ranger335v

    ranger335v Well-Known Member

    A sharp shoulder resists forward case movement from pin impact and primer detonation so they resist the shoulder movement that allows case stretching during firing. Tapered shoulders push forward easily, that's why so many tapered cases have rims or belts.

    Venturi effect occurs when high speed gas flow moves from a small diameter to large.

    Straight wall cases do tranfer pressure more efficently than bottle neck but that efficency is irrelivant for anything but small cases in short barrels such as handguns. Bottle neck cases hold much larger amounts of much slower burning powder and that allows the pressure:time curve to be extended for much higher velocity. At a pressure of 55,000 psi the gas is some 3,700+ times as dense as air so it's about as viscous as honey as it flows out of the case. (High viscosity is part of why so little pressure is lost at the cylinder gap of revolvers.)

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