What creates a strong cartridge?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by laserflat, Jan 19, 2013.

  1. laserflat

    laserflat Well-Known Member

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    Specifically, what allows a cartridge such as the .338 Lapua handle such high pressure? Is it just the thickness of the case web/primer pocket area or the quality/hardness of the brass or both?

    Thanks
     
  2. Joe King

    Joe King Well-Known Member

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    No compromise quality control and damned good engineering.
     

  3. Greyfox

    Greyfox Well-Known Member

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    I believe that it is both, with two independent aspects that create a strong cartridge. First is the inherent design, the second is quality of the of the manufacturing process. The high pressure, magnum cartridges generally are designed with attention to case head thicknes, case expansion dynamics, web, primer pocket etc. The design can be excellent, but if the manufacturing process doesn't meet the design specifications, like dimensional specs, hardness, and the composition of the brass itself, the design benefit is lost. If the manufacturing process is poor, this might not show up at all on the first shot with the cartridge, but certainly will once you begin the reloading process. I have experienced this on several occasions, with well designed cartridges. With their focus on not only cartridge design but also the reloading after market, Lapua does an excellent job with both, as demonstrated with he 338 Lapua.
     
  4. woods

    woods Well-Known Member

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    Here is a list of SAAMI pressures for different cartridges

    Max Chamber Pressure - SAAMI Specs

    Notice the 338 Lapua listed no standard pressure, but I would be surprised if anyone was running a load much over the 65,000 psi standard for modern high pressure calibers like the RUM's and WSM's. IOW the 338 Lapua case should not have to withstand anymore pressure than a 338 RUM, or a 300 WSM or even a 270 Winchester

    Pressures are regulated by the amount of powder, burn rate of powder, chamber dimensions, bullet weight and bore size so that it would not matter if you were loading 91 gr of RL22 in a 338 RUM or 69 gr in a 300 WSM you would get the same approximate pressures.

    Therefore the pressure on the brass is the same in both

    Now if someone can show me where the accepted pressure for the 338 Lapua is more, say 75,000 psi, then I would say that Lapua has a metalurgical secret that they use in the their "super brass"
     
  5. lloydsmale

    lloydsmale Well-Known Member

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    got to agree. Weatherby been loading to that level for years and there brass is nothing special. Id say its a combination of the fact that guns are made with better steal quality then they were many years ago and liability has scared the ammo manufactures into neutering most of there ammo so a guy thinks it takes something real special to do what was done 40 years ago with guns that werent as good as there selling right now. Most of the guns out there chambered for it are quality factory guns or customs that are built no expense spared so im sure there not so gunshy about publishing loads up to its true potential. Not much chance someones going to chamber an old 93 mauser in a round like that!
     
  6. laserflat

    laserflat Well-Known Member

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    Im not saying its anything magical. But I didnt think it was a secret that .338 Lapua brass, and all Lapua brass for that matter, holds up under many repeated full-tilt loads better than most other brass..

    Thanks for the replies yall, anyway, I was wondering if you took, say, the .50 BMG, which is fairly low pressure compared to modern magnum rounds, and doubled the thickness of the brass throughout most of the case, and had very high quality brass used, would it make very much difference in how much pressure it could handle? Assuming you have an action that can handle it of course.. Or does the case head size dictate that theres going to be so much bolt thrust, that case thickness doesnt matter much at that point?

    Thanks again
     
  7. Beng

    Beng Well-Known Member

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    The production process, especially the right mix of case hardening via forming and anealing gives a case the right properties.
    The less steps you take, the less the cost, but also the less ductile the case will usually be.
    Thickness and brass' (educt) quality are of course important too.
     
  8. Mikecr

    Mikecr Well-Known Member

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    In Quickload, the 338LM is SAAMI max at 60Kpsi, which implies that it's not a 'high pressure' design compared to many other cartridges.

    There would also need to be further qualification of the inquiry "handle such high pressure" -to answer the question. After all, what do you mean by HANDLE?
    Handle as in lasting brass life?
    Easy extraction after a few stiff loads?
    Not blowing up with stupid loads?
    Primer pockets staying tight?
     
  9. Beng

    Beng Well-Known Member

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    The .338 Lapua had a max pressure of 450Mpa (About 65 kpsi) for a long time, it was decreased a few years ago though.
    As far as I heard, the problem was not the case itself but the force acting on the bolt face, due to the big base diameter and thus area (F=p*A).
    The european proofing might have had an influence on that, rifles are proof fired with a 125% pmax load. Actions not suited to cases that big had problems handling the forces applied to the boltface (increasing headspace &c).
    Military loads were not affected though.
    The load the british military uses in their L115 sniper rifle is still a high pressure load which propels the 250gr LockBase bullet to about 3050fps.

    A lot of this is hearsay I must admit, I read it on forums, though it makes sense to me and the people who gave the information were as reliable as Shawn Carlock (experienced wildcatters with good connections to the industry).
     
    Last edited: Jan 24, 2013
  10. Greyfox

    Greyfox Well-Known Member

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    I responded previously on this thread with the standard answer of basic design, quality control etc. While this is certainly important and everyone is pretty much saying the same thing, I have thought more about it. Given those basics, after many years of working with lots of different rounds, the strongest, longest lasting cartridges have been the ones that give me the required accuracy, velocity, and distance, when my load is built to work well within the maximum SAMMI pressure of the cartridge, and, importantly, the rifle chamber has the correct dimensions. I have had 308's and 223's that a 100 box of Lapua brass gets me over 1500 rounds down the barrel with maybe a few annealings required. One the other hand, I have just stretched slightly the limits of the same cartridges and they fall apart in a few reloads with case head separation, loose primer pockets, etc. and the initial pressure signs were not always obvious. I have a buddy that uses one box Lapua of brass per barrel with his 6BR. Overall, I think that given the basic design and manufacturing process is sound, the specific load and rifle combination is what creates a strong cartridge.IMHO.
     
  11. lloydsmale

    lloydsmale Well-Known Member

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    the right answer