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.308 Win Reloading pressure observation in manuals.....

Discussion in 'The Ammo & Reloading Forum' started by bluesea112, Jul 18, 2007.

  1. bluesea112

    bluesea112 Active Member

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    I have not yet begun reloading, because I have spent all of my free time reading reloading manuals. I now have Lee, Lyman, Hornady reloading manuals, and after reading each of them, I have made an interesting observation that does not make sense to me.
    When comparing load information for .308 Winchester in a 180gr jacketed bullet, I noticed that IMR4895 lists a maximum load pressure of 50,900 with a velocity of 2540fps. The H-VARGET maximum pressure is listed at 59138 with a velocity of 2661. If the .308 pressure can safely be 59,000, why don't they increase the IMR4895 grains slightly to raise the velocity. Why stop 10,000 psi short when loading with IMR4895? That extra 10,000 psi could dramatically increase bullet velocity.
    I'm sure I am missing something here, but I cannot figure out what it is. Maybe I just need to stop studying and actually start doing. I would probably learn the reason very quickly.

    Bluesea112
  2. bluesea112

    bluesea112 Active Member

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    After making that post I looked down at my manual and the answer stuck out like a sore thumb. The IMR4895 is a compressed load! Whew, I feel much better now. I knew there had to be a logical reason.
    Now that I know that, I think I will use IMR4895 until I learn a little bit more about reloading. If compressed IMR4895 only reaches 50,000psi, there is a 10,000 psi safety built into the reloaded round. There will be no possible way for me to overcharge/overfill a 180gr bullet, correct?
  3. Mark

    Mark New Member

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    You will probably notice that different manuals list different velocities with the same amount and type of powder. Remember this information is what they found with their rifles. You have to remember not every firearm holds the cartridge the same. For example, a Mauser 98 has an unsupported section at the base of the cartridge. The Rem. 700 does not. Even though both rifles may handle 59K, the brass cartridge will start to flow at pressures lower than this. Manual maximums are what the publishers found in their test firearms. They will vary.

    Your firearm is an individual. The one coming right behind it on the line may appear the same, but they are not identical. There is nothing in the rules that states both rifles will handle the same load exactly the same.

    You are doing the right thing to read and notice differences. Manuals are a guide, and provide a place to start. Be safe.
    Mark
  4. LASSIE

    LASSIE New Member

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    Location:
    terlton, OK.
    Bluesea112
    While you are looking at IMR 4895 here is a load that is very accurate in my Savage bvss.
    168 Sierra match king
    IMR 4895---39.5 grains
    Winchester Brass
    CCI 200 primer
    2450 FPS
    less than .5 group @ 100 yds. 10 shots
  5. Popgunner

    Popgunner New Member

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    One difference you may see is that some load manuals use the system where they load a combination of components till the case expands .001" & then they reduce the powder charge a standard amount-say 6% or whatever they decide. they then publish the -6% load as maximum. A 6% reduction of different powders would not always result in the same pressure.
  6. LDBennett

    LDBennett Well-Known Member

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    You need multiple manuals as each has a litttle different coverage of reloading. To get it all you need to read them all.

    Several things make reloading more of an art than science when using reloading manual data. No two manuals use the same gun or universal receiver or same barrel length or same twist or same brass or same primer or same almost anything. Add to that the intermixing of Copper Units of Pressure (CUP) and the Pounds per Square Inch (PSI), which are not interchangeable at all.

    CUP is the crushing of a copper cylinder by the case pressure in a specially prepared case and tooling. It measures the work done to crush the copper cylinder. A calibrated chart is used to go from inches of crush to the CUP number. It is kind of an average work done measurement. PSI is an electronic pressure transducer (converts force to voltage) where an oscilloscope picture of the pressure over time is recorded. The reported pressure is the peak. So when CUP and PSI are compared we would be comparing work done with peak pressure..... not things that should be compared. The CUP system was first and slowly the reloading industry is converting to PSI but today the manuals mix the numbers. So be careful of which a specific piece of data is.

    I find a manual load that kind of matches what I want to use (powder or bullet or ? ). I stay below their max and start at their starting load. The velocities that they acheive are good for comparison in their manual but not much good for comparison to other manuals.

    LDBennett
  7. bluesea112

    bluesea112 Active Member

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    Thanks for the feedback. I am still learning, so I appreciate all the tips I can get.
  8. DWARREN123

    DWARREN123 New Member

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    Also, quite often the max load is not the most accurate load.
    I understand that CUP and PSI is not the same but I also understand that commercial testing uses a sensor in the center of the chamber while the military puts the sensor at the case mouth area, if so then the pressures would be different for the same or similar cartridges (i.e. 5.56X54mm and 223 Rem).
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