excess pressure?

Discussion in 'Reloading' started by bigry26, Feb 7, 2012.

  1. bigry26

    bigry26 Well-Known Member

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    how much is too much? I have some very faint ejector marks and there is some brass specks on the bolt face with 92 grains of retumbo. This is brand new Lapua brass. I like this load but I dont want to screw anything up. How much shouldI back down from here? The mark is just below the trademark L. Ryan
     

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  2. webs

    webs Well-Known Member

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    What bullet are you shooting?
     

  3. bigry26

    bigry26 Well-Known Member

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    I am shooting 300 grain smk's in a savage 110 fcp. Ryan
     
  4. Hookturnr

    Hookturnr Well-Known Member

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    I normally back up .2 and call it a day if Im doing my load dev, in the summer, if not then I'll back up .2 at a time as temp goes up until I'm at my max average ambient air temp with no ejector stamp
     
  5. Mikecr

    Mikecr Well-Known Member

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    Not knowing anything about the cartridge, and solely based on the picture, I don't see any problem.
    Is there difficult extraction?
    Any issues in sizing this brass?

    A little brass on the bolt face, slight ejector marks, flattening of primers(not failing),, seems normal and fine to me.
    I get this with a bunch of cartridges that are NOT loaded to high pressures, and the brass is lasting forever.
     
  6. backwoods83

    backwoods83 Well-Known Member

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    Most everything 85% of what I shoot are savage rrifles and a lot of them will leave just a slight ejector mark, especially when they are newer and the ejector spring has heavy tension. As long as bolt lift is still easy I see no reason to change it, there are no obvious signs of pressure on the primer so I wouldn't change it. I get that mark on mild plincking loads sometimes, if you can't find anyother sign of pressure then its likely just the ejector.
     
  7. Reloader222

    Reloader222 Well-Known Member

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    I copied this from some site - sorry I did not make a note of where to find:

    "The way to tell if the pressure is low:

    1. Unburned powder in the barrel pretty much always means low.

    2. Primer backed out of the primer pocket (i.e., not flattened) usually means low.

    3. What does the manual say? If you're at the lower end of recommended loads, then the pressure is probably low.

    The way to tell if the pressure is high:

    1. Sticky ejection. If ejection is sticky in a clean firearm in good mechanical condition then the pressure is high.

    2. Primer flattened clear out to the edges.

    3. Loads at the upper end of those recommended in a manual.

    4. Blown or pierced primers.

    5. Rapidly expanding primer pockets on reloading and/or poor brass life. Defective brass can also cause these signs.

    6. Group sizes that have been decreasing as a load is increased and then start to widen again.

    7. Cases from a semiauto that have been landing in about the same place and then start to be thrown erratically to markedly different places.

    8. Cases from a semiauto on which scuff marks start to appear on the body of ejected cases.

    9. Extractor marks swaged into the case head.

    I've probably missed some.

    You have to know an individual gun as well because different guns and different actions types will show signs of pressure in different sequences.

    Now I'm sure you've all heard about light powder charges in large capacity cases using slow powders (it can happen with fast powders as well). The result can be high pressure signs like flattened primers, splintered stocks and sticky ejection as well as hang fires. What happens is that the bullet starts to engage the bore but the pressure isn't quite high enough to push it clear through. The powder is still burning and the pressure keeps rising until it's high enough to push the bullet that was kind of stuck, out of the bore. As we all know, it takes quite a bit less pressure to get a bullet going down the bore with a little jump between the bullet and the lands than to start a bullet that is already engaging the lands. You might think of it as the closest you can get to a squib load (a load with which the bullets remain in the bore) without having a squib load.

    So, in the latter case, though the load is light, the pressure is quite high. In other words, case head smearing, sticky bolt lift, very flattened primers are signs of high pressure even if the powder charge is low unless the chamber is dirty or there is some mechanical defect in the firearm."


    According to my observation you do not have a high pressure sign. The primer is not smeared in the primer pocket and is not flattened. I would say this is a good pressure load given that all other conditions are favourable. Lastly when you press the primer out and you look at it with multiplyer glasses and you see a "flat-hat-top" you have high pressure, but when the top of the "hat" is still rounded, pressure is still fine.
     
  8. boomtube

    boomtube Well-Known Member

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    I've reloading for a very long time and usually load pretty 'hot' but have never blown up anything nor had a head seperation. Some things I've learned about pressure are:

    * primers are such poor indicators of pressure I hardly pay them any attention. Excessively flat primers are most often a sign the case shoulders have been set back too far. Pierced primers most often signify a bad firing pin or one that's too small for the bolt hole. Primers that blow out at the edge of the pocket usually have defective cups OR the hole's radius is too large.

    * ANY visable sign of high pressure on the case head is too hot, it takes a lot of pressure to make even a faint impression at the ejector/extractor location.

    * Any measureable expansion of the head diameter just forward of the extractor groove says the load is too hot.

    * A case with no obvious sign of over pressure but the primer pockets get looser each firing IS over loaded.


    There's no magic 'back off' number for the charge; back off until you're consistantly below where the signs appear.
     
  9. Mikecr

    Mikecr Well-Known Member

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    I start load development by finding MY 'max load' with given components.
    This has nothing to do with any load manual or velocity goal.
    It's based on max load being a reloading problem, or not.
    A defining line.

    Bring calipers to the range when working up to find max. Pick a spot nearest the webs that you can consistently measure at(I use the webline ~.2 forward of extraction groove).
    As you go up in pressure this datum will step change to a larger diameter that represents chamber minus springback. It'll hold at this diameter for further increments, but at some higher charge will step change again another .0005"(1/2thou). This represents the point of brass yielding and where FL sizing will be required. Barely above this you get popping extraction as the brass is left at an interference fit because the chamber sprung back fully, while the brass did not(yielded).

    Primers,,, bolt turn,,, head marks,, brass life,, could do anything, or nothing, through the range -with your action, your chamber, your dies, and what you're willing to accept. Many point blank BR shooters accept only 2-3 firings of brass life with extreme pressure loads. But you can't accept their pressures with hunting cartridges. Too much area for pressure applied. You will run into real problems way lower in pressure.
    Your chamber is your best die, and you're sizing in it (upsizing). So this will show any real problems, or not.
    That's what you wanna watch.
     
  10. bigry26

    bigry26 Well-Known Member

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    could the oal be a factor in the pressure? Ryan
     
  11. Mikecr

    Mikecr Well-Known Member

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    A lot of things combine to produce different pressures with a given load.
    OgvOAL matters in that pressure step changes upward as a bullet contacts the rifling lands.
    Bullet seating depth matters in that deeper seating increases load density a small amount, but in an extreme can compress a load. Also an extreme is seating to put bullet bearing into the neck-shoulder junction, where tension(bullet grip) sharply increases.

    These are not always 'problems'. Many develop great loads with bullets jammed into lands, or seated deeply due to magazine restrictions.
    But they can cause your pressures/velocities to differ from book listed.
    Many other things can as well.
     
  12. CogburnR

    CogburnR Well-Known Member

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    I have pretty much ended up doing the same thing as Mikecr with measuring the cases.

    FWIW, I measure the case head expansion on factory loads and then I usually end up with slightly less expansion in my hunting loads.


    I have a rifle that makes a ring around the primer with loads that are not overpressure. I found that it is very sensitive to case length and likes cases to be closer to trim length than the published length.
     
  13. Bart B

    Bart B Well-Known Member

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    I asked SAAMI about this some years ago when I started reloading for my first belted magnum. The rep said most cartridge brass starts extruding into bolt face cutouts (ejector holes, slots, etc) at about 65,000 CUP. If any signs of it happen, you're near the edge of the safety cliff and you better back your charge weight off if safety is any concern whatsoever.

    The picture clearly shows signs of it.

    Cutting your charge back 2 or 3 grains may be all that's needed. Maybe more. Depends on how much of a safety margin you want.
     
  14. lloydsmale

    lloydsmale Well-Known Member

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    If i dont get at least 5 firings out of brass before the primer pockets open up to much i will back it down till i do.