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Signs of pressure

rotaxpowerrotaxpower Member Posts: 215 ✭✭✭
Does anyone have any good, detailed pics of primers that have been subjected to high pressure loads? I new reloader so I dont have very much experance with pressure, and I always keep my loads very mild too. Thanks!

Comments

  • bpostbpost Member Posts: 32,220 ✭✭✭✭
    edited November -1
    A flat primer may not be a true indicator of excessive pressure. A primer that has flattened to the point where it fills the entire primer pocket making an almost smooth base on the case is a pretty good indicator that pressures are getting out of hand.

    If you shoot mild lods listed in the book you have nothing to worry about.
  • nononsensenononsense Member Posts: 10,934 ✭✭✭✭
    edited November -1
    rotaxpower,

    bakdout.jpg

    Backed out primers: This condition is predominately caused by low chamber pressure rather than oversized primer pockets. When struck, the ignition pressure of the primer compound drives the primer slightly from the cartridge case. The powder charge is then ignited and, under normal operating pressures, the case will follow the primer to the breech face of the firearm, seating the primer, resulting in a normal fired case/primer appearance.

    When a power charge does not generate sufficient pressure, the primer charge will still back the primer out, but there will be insufficient pressure for the cartridge case to follow and the primer will be left protruding slightly from the case. If the problem were a loose primer pocket, the case would still have enough pressure to be driven back flush with the primer.

    Not that this has ever happened to me, but as you can see from the lifelike artist rendering on the right - The rim looks normal, the primer is backed slightly from the primer pocket but retained a normal fired appearance. There is no flattening of the primer face or signs of leakage.

    crater1.gif

    Cratered or extruded primers: "Cratering" is the result of primer material being extruded or pressure formed into the firing pin opening on the recoil face of the slide. Very minor narrow ring around a firing pin indentation is typically caused by excessive clearance between the firing pin and firing pin opening in the slide. Larger areas of cratering, as illustrated in the picture on the right is generally caused by excessive pressure.

    DSC03183-copy.jpg

    Flattened Primers as a function of pressure: Flat primers exist in degrees, and the degree determines cause. As seem to the right - a primer flattened around the face and firing pin indentation would normally be viewed as a primer exposed to high pressures, as long as the radius along the perimeter of the primer was intact. A primer flattened across it's entire surface where the normal gap between the cartridge case and primer radius is essentially gone, is usually attributed to head spacing.

    All in a row:

    primesamp.jpg


    Best.
  • JustCJustC Member Posts: 16,055 ✭✭✭
    edited November -1
    here is one of excessive headspace and flattening that nononsense described. The left is correct headspace and the right in too much.

    100_0251.jpg
  • n/an/a Member Posts: 168,427
    edited November -1
    quote:Originally posted by JustC
    here is one of excessive headspace and flattening that nononsense described. The left is correct headspace and the right in too much.

    100_0251.jpg


    Hey JustC...what exactly distinquishes this primer from a high pressure primer??? From looking at your pic there, I would have assumed that pressures were running a little high...I would not have thought it to be a head space problem. I've had many primers that flat before. Any help here would be appreciated!![:)]


    EDIT: Never mind...I see now. The radius is filled in. Thanks! Although...I still think I've had primers that flat before.[^]
  • rotaxpowerrotaxpower Member Posts: 215 ✭✭✭
    edited November -1
    Awsome, Thanks for the pics, and the help![:)]
  • JustCJustC Member Posts: 16,055 ✭✭✭
    edited November -1
    Eric,..look just ahead of the casehead on number 2 case. You will see the shiny line across that casehead that shows an incipient casehead seperation due to the excessive headspace. These 1x fired cases are from my rifle (left pic) But the right hand case showes excessive HS fired in what seems to be an excessive headpaced chamber. Too much headspace will yield this look every time. My rifle with that brass is fine, but the rifle those cases were fired in shows excessive headspace. That is the difference. Same load,..different chambers.
  • steve4102steve4102 Member Posts: 186 ✭✭✭
    edited November -1
    JustC, I apologize for my ignorance, but, I don't see any diff. between the two.

    quote:look just ahead of the casehead on number 2 case. You will see the shiny line across that casehead that shows an incipient casehead seperation due to the excessive headspace.

    I see a shiny ring around the case just ahead of the casehead on #2, but, I also see the same ring in #1 it just seems a bit closer to the head. The only diff. I see between #1 and #2 is, #2 looks to have more of a flattened primer.

    Please don't think I am flaming you or anything like that, I just have a tough time with pressure signs and head space and cup and psi and I just want to make sure I know what I am looking at and what to look for.
    Thanks
  • deceedecee Member Posts: 456 ✭✭✭
    edited November -1
    What exactly is headspace?
  • nononsensenononsense Member Posts: 10,934 ✭✭✭✭
    edited November -1
    decee,

    Headspace is the measurement between two points in a rifle's chamber. These points are the boundaries of cartridge movement when a cartridge is chambered. In strict SAAMI terms headspace is the distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.

    OR this is what has been used here on Gunbroker before:

    In simple terms, headspace is the dimension of the chamber of your rifle, the gap between the face of the bolt and the stopping surface for the cartridge. On a rimless cartridge such as the .308, the stopping surface is the shoulder. To be precise, it is the distance between the face of the bolt and the datum line, which is a circle of stated diameter, along the slope of the shoulder of the cartridge.
    On a rimmed cartridge like the .30-30 or .303 British, the headspace is the gap for the rim.

    On a belted magnum, headspace is the gap for the belt. Since not every rifle or cartridge can be made to exact dimensions, with perhaps the best custom rifles being one exception, headspace is deemed to be correct if it is within a certain range.
    With rimmed cases, the rim keeps the case from moving forward at the blow of the firing pin. Similarly, the belt on belted magnum cases maintains headspace. That's one reason why wildcats based on the belted H&H magnum case became so popular.

    These are the types of gauges that we use to check headspace:


    headspacegauges.jpg


    This is an example of headspace for a rimless cartridge:

    Headspacerimless.jpg
  • JustCJustC Member Posts: 16,055 ✭✭✭
    edited November -1
    Steve, look at the primer on the right. That primer has filled in the primer pocket from side to side with little or no radius left on the primer. However, this primer shows NO cratering around the firing pin strike. That coupled with the bright ring just ahead of the rim/extractor groove, tells me it is a headspace issue and the case grew in length enough to thin out in 1 firing (hence the shiny ring) and the primer was slammed back against the boltface as the round was ignited. That is what flattened the primer, not pressure.

    Pressure will usually be accompanied by shiny ejector marks, stiff bolt lift, and/or some cratering around the firing pin strike.
  • n/an/a Member Posts: 168,427
    edited November -1
    quote:Originally posted by JustC
    Eric,..look just ahead of the casehead on number 2 case. You will see the shiny line across that casehead that shows an incipient casehead seperation due to the excessive headspace. These 1x fired cases are from my rifle (left pic) But the right hand case showes excessive HS fired in what seems to be an excessive headpaced chamber. Too much headspace will yield this look every time. My rifle with that brass is fine, but the rifle those cases were fired in shows excessive headspace. That is the difference. Same load,..different chambers.


    I saw the ring...but I would not have been able to tell that it was a head space problem from the primer alone. Quite a few of my loads flatten the primer till they fill most of the pocket...without the ring of course...and with no other high pressure signs, such as a sticky bolt, etc. If your case did not have that ring on it, I would not have been able to tell there was a problem...
  • JustCJustC Member Posts: 16,055 ✭✭✭
    edited November -1
    Eric,..I more or less knew it because I saw some that had actually cracked, and knew they had only been fired once (factory ammo)[;)]
  • deceedecee Member Posts: 456 ✭✭✭
    edited November -1
    Thank you Nononsense.

    I take it the most common problem is excessive headspace as opposed to the reverse. Could this be simplified into saying that the cartridge had a loose, sloppy fit in the chamber?


    What is the cause of this? Is it an incorrect chamber size or incorrect brass size?

    I would think that as brass is reused, it lengthens and creates a smaller headspace. Wouldn't brass fired in the same rifle form itself to the chamber?
  • JustCJustC Member Posts: 16,055 ✭✭✭
    edited November -1
    it will only stay formed to the chamber if you neck size of partial full length size. If you FL resize, it is made smaller than the chamber every time you size it. This overworking of the brass will cause the case-head seperation situation much faster.

    too little headspace and the bolt won't close.

    too much, and the case is actually driven foreward by the firing pin strike, and when it ignites, it is slammed back against the bolt face and flattens the primer which at that point, has started to back out of the primer pocket because there was initially no boltface there to hold it in place.
  • RCrosbyRCrosby Member Posts: 3,793 ✭✭✭
    edited November -1
    Keep in mind also that primers vary greatly in the characteristics (hardness, etc.) of the cup material, and that while one primer might give what many would clearly interprete as borderline pressures well before the point of any real problem, others may look "normal" despite dangerously high pressures.
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