High Pressure Loads in 700 LA

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Big-un, Mar 19, 2006.

  1. Big-un

    Big-un New Member

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    I am running a pretty stiff load of Retumbo in my Sendero STW. Is there anything the smith can do when I send it in to make it more able to handle these high pressure loads a little more safe?

    Thanks
    Big-un
     
  2. Varmint Hunter

    Varmint Hunter Well-Known Member

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    Yeah - Have it rechambered to 7RUM. Better than blowing the rifle apart. /ubbthreads/images/graemlins/grin.gif
     

  3. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    What do you mean "Handle these high pressure loads a little more safe?"

    Are you seeing problems as a result of high pressure? Only thing to really do is rebarrel with a very tight spec chamber, tighten up the bolt nose to barrel recess fit, Bush the firing pin hole for a smaller diameter pin(Helps prevent primer cratering).

    Other then that, there are reasons we watch for pressure signs, to keep us out of serious trouble. No quality smith in the world will take on this job so you can up the pressure even more then you can. There is a limit in which you should load any rounds.

    Take the advice offered. If you want more performance, get a bigger engine, 7mm RUM would be a decent start but there is more out there!!! /ubbthreads/images/graemlins/grin.gif

    Kirby Allen(50)
     
  4. davewilson

    davewilson Well-Known Member

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    i would say the only way to "handle the high pressure loads a little more safe" would be to put the barrel on a stronger action.

    all kidding aside, back your loads off, you're heading in the wrong direction.
     
  5. Bart B

    Bart B Well-Known Member

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    Forget doing anything to make the receiver or even the barrel stronger to handle high pressure loads safely. Your rifle will easily handle loads producing up to about 130,000 psi. They all will do that. The problem doesn't exist with the steel in the rifle.

    The problem is brass cases. Nobody makes cartridge cases that handle pressures higher than about 70,000 psi. That's the point they start extruding back into the bolt face through the ejector hole/slot and expanding primer pockets such that they won't hold primers any more.

    One solution is to have some high quality steel cases made that will withstand the high pressures you want. These cases won't be able to be reloaded, but at least you'll reduce the chance of having a case rupture and let high pressure gas blow back into your face and ruin your day.

    A better one is to back your loads off or use a larger cartridge case big enough to get the muzzle velocity you think you need.

    To answer you question: Yes, your 'smith might be able to make some steel cases for you to use......once, then throw them away.
     
  6. budlight

    budlight Well-Known Member

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    [ QUOTE ]
    I am running a pretty stiff load of Retumbo in my Sendero STW. Is there anything the smith can do when I send it in to make it more able to handle these high pressure loads a little more safe?

    Thanks
    Big-un

    [/ QUOTE ]

    What exactly is your load and what is it doing to case right now? I'm an long time 7STW man.
     
  7. Varmint Hunter

    Varmint Hunter Well-Known Member

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    [ QUOTE ]
    Forget doing anything to make the receiver or even the barrel stronger to handle high pressure loads safely. Your rifle will easily handle loads producing up to about 130,000 psi. They all will do that. The problem doesn't exist with the steel in the rifle.


    [/ QUOTE ]

    I am NOT a gunsmith so excuse me if I'm off base here. Doesn't running 100,000psi+ loads set locking lugs back, cause metalugical stress fractures and eventual fatigue &amp; failure? I'm guessing that your claim may have been misleading.
    No flame intended.
     
  8. sullijr

    sullijr Well-Known Member

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    No.I think you are trolling.
     
  9. Bart B

    Bart B Well-Known Member

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    You're not off base and I don't have a fire extinguisher ready. You bring up a good point.

    The tensile strength of most modern centerfire bolt actions is in the 120K to 150K range. Remington and Winchesters are in the middle of that range. I remember this from an article many years ago. Bolt lug hardness and steel type is typically enough for about 140K ppsi.

    Proof pressure for the .308 Win. is about 90,000 ppsi but it's normal operating max pressure is about 63,000 ppsi. Many modern cartridges have similar numbers. That's a ways from setting the bolt lugs forward or recess faces back even if several proof loads are fired. I've seen some fired proof load cases and they wouldn't hold a primer.

    Dan Lilja's web site has some info on bolt strength.
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    VH,

    Most cases will have their primer pockets loosen up at around 65,000 psi depending on the chamber fit to some degree. Some will loosen at a bit less, some a bit more. The 338 Lapua case from Lapua is probably the strongest case I have every used and it will even loosen primer pockets at around 70,000 to 75,000 psi no matter how tight the chamber is fitted.

    Point being, you are correct, the case and primer are the weak link here. All will fail well before 100,000 psi, which is a good thing.

    Another tid bit of information. In gunsmithing school the topic of detonation came up. If you learn about this occurance with large capacity case designs you would NEVER push a load to primer pocket loosening levels ever again.

    Basically what happens is that once the internal pressures reach a point of around 70,000 to 75,000 psi, detonation occurs. What detonation is is when all the remaining powder in the chamber and bore burn nearly instantaneously because of this pressure level.

    In most cases, there is not a dramatic amount of powder remaining when this occurs so the results are not dramatic, generally a loosened primer pocket.

    In extreme cases where there is a very large case capacity and relatively small bore, serious strain can be imposed on a receiver.

    Using the correct burn rate of powder will greatly control any serious happenings but if you use a powder that is a bit quicker then it should be for a specific case volume you can get into trouble.

    Actually using a burn rate slightly slower then needed will generally always keep you out of trouble. The reason why, because you simply can not reach this 75,000 psi range with the amount of powder you can fit in the case with proper weight bullets used.

    Point being, load to pressures that are under what will loosen a primer pocket. If your getting at least 3 firings per case without loosening primer pockets your in good shape, top load levels but good shape.

    If you need more performance, get a larger engine to do the work.

    I would tend to agree with you 100%.

    Kirby Allen(50)