The first sign of excessive pressure is...

Discussion in 'Reloading' started by buckbrush, May 28, 2009.

  1. buckbrush

    buckbrush Well-Known Member

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    ...flattened primers? Then ejector marks? Then sticky bolt?

    Just curious. I am working 7 mag loads and am already 1 grain hotter than the Berger manual and the primers look like they did before firing (with the exception of the firing pin dent of course).

    Thanks.
     
  2. Seven Oaks

    Seven Oaks Well-Known Member

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    Do your case heads have rings on them? If they don't, the primers aren't flattened and your not having difficulty lifting the bolt, I would guess your ok.

    But if your over what the manual says you can bet your getting real close...

    Be aware that if you try to seat your bullets farther out touching the lands or let your brass necks get to long and it crimps the bullet when you close your bolt you could be in for a suprise. Either of these will cause a dramatic spike in pressure and since your already at the edge
    there is no room for error. Keep a close eye on you brass neck length and bullet seating.
    Best,

    Dee
     
    Last edited: May 28, 2009

  3. AJ Peacock

    AJ Peacock Well-Known Member

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    I use velocity as the first sign of excessive pressure. You don't get velocity without pressure and higher pressure nearly always means higher velocity. If you shoot over a good Chronograph and keep the velocity in the expected range (and use appropriate powder/bullet combo's), you will stay in the safe zone.

    Just remember, there aren't any 'magic' combinations that give super high velocities with low pressures. There is no free lunch.

    AJ
     
  4. jimbires

    jimbires Well-Known Member

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    I use a blade micrometer . measure the case head before you fire and measure it again after you fire . it should be expanded about .0005 max . that's half of a thousandths . make sure to put the mic in the same location . I align the one blade up with the " 7 " on the head stamp . my 7 rem mag makes the federal primer look like a top hat with the minimum starting load , so I have used case head expansion for my pressure indicator . on the belted case I measure right on the belt . Jim
     
  5. AJ Peacock

    AJ Peacock Well-Known Member

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    Jim,

    In the past, I also used visual inpection of the brass, case head measurement and bolt lift/extraction as pressure signs. A couple years ago, I read an article about pressure and it changed my entire perspective on pressure/velocity and pressure signs. The author shows that from a statistical perspective, throwing a dart at a wall is about as good to indicate pressure as case head expansion is.

    Here is a link to the paper.
    http://www.shootingsoftware.com/ftp/...%2019%2004.pdf

    I still monitor my brass and extraction, but I rely more on velocity. As long as I'm using an appropriate powder/bullet combination for the rifle, with published loads to compare velocities with; I trust the velocity I'm getting is a very good indicator that I am in a safe zone.
     
  6. jimbires

    jimbires Well-Known Member

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    AJ , I'll check the article out . I'm sure the measuring method , that I use , is not 100% . one flaw I see is , as the brass work hardens it will not expand as easily . thanks Jim
     
  7. AJ Peacock

    AJ Peacock Well-Known Member

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    He discusses both measuring difficulties as well as brass hardening in the article. I was very impressed with the article and it changed the way I did things. I'll be interested to find out what your impression of the information is.

    Take care,
    AJ
     
  8. Michael Eichele

    Michael Eichele Well-Known Member

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    I am with AJ for the most part here.

    I shoot most of my rounds over a chrony and ALL of my developmental loads over a chrony. The first thing I see before even lifting the bolt is the velocity reading. Most of the time I can predict whether or not the bolt will be sticky.

    There are times however that I have pressure signs at lower than expected velocities and absolutly NO pressure signs at higher than expected velocities. It all depends on the primers, bullets, barrel quality, chamber demensions, twist, barrel length, how far off the lands you are AND whether or not all of these and more factors like the burn rate of the powder youre feeding it.

    Pressure curves are also another complicated issue. You can still have HIGH pressure without pressure signs.

    For me, I stop the ladder test as soon as I feel an abnormal bolt lift. It doesnt have to be sticky, just abnormal. Then I look for ejector marks, cratered primers and flattened primers. I pay no attention to the case head. Another BIG sign is loose primer pockets. Not neccesarily after many firings but if after one or 2 firings you dont have any resistance when seating a primer, it is time to back way the heck off. If I have even one sign, I stop and back off to the next charge weight below the last and I use that as a reference as my "max" load. Then I usually pick the most accurate load from the session below that one for "breathing room". In some cases, I will use a lower charge than max for most of my shooting and hunting but a max load where I know temps will be well under the mark when I developed the loads provided the accuracy is good at max. Most of the time it isnt.
     
  9. royinidaho

    royinidaho Writers Guild

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    AJ and Michele seem to have developed a good process. My process is quite similar but depends on the chamber.

    I've passed on the primer flattening though it is a bit of an indicator of things to come.

    The shiny extractor mark is an indicator that says I've gone to far. I don't think the cartridge can 'fire' straight with the bump on one side.

    On my REM 721 if there is the slightest of clicks as the bolt handle reached the top of its movement is the indicator that I use on that rifle. Any more powder than that needs one tap very firm tap to the rear by the hand to extract the case the first short amount.

    I hate an early discard of brass which determines my working velocities.

    Also, the RSI lab is a neat tool for factory cartridges where ball park pressures are published. Between the RSI and a good chrono you have it pretty much nailed.

    On a wild cat it takes a little more shooting to determine an max pressure goal.
     
  10. jimbires

    jimbires Well-Known Member

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    the article is very informative . it sure gives me more to think about . I feel like the rug was pulled out from under me . LOL I have noticed that it is hard to measure tenths on the case head , you have to be really on your game . I made a little block of wood to hold the case so I had both hands free .
    I don't want to hijack the thread but this is what the original guy was asking and this info should or could help him too . you said you look at velocity as your primary pressure indicator , and I see your point of view . I've been playing with a 300 wby so it's still fresh in my head , and I have all my notes yet . I'm using a nosler ballistic tip 180 grain , with H1000 powder . my Nosler book says that starting load is 85.0 @ 3012 fps , and max load is 89.0 @ 3146 fps . I've found a node at 87.8 that shoots about .5" @100, and good extreme spread . it shows nice pressure signs . primer looks good . I'm using winchester mag primer ,I can get them easier . bolt works good . case head expansion is about .0003 . I use a chrony beta ,but my velocity is 3170 fps . by your method this load is too hot , because I have exceeded the book max velocity with a lesser amount of powder . am I correct ? I have not shot any of the brass cases enough to find the point of primer pocket stretch . thanks Jim
     
    Last edited: May 28, 2009
  11. AJ Peacock

    AJ Peacock Well-Known Member

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    I had a Chrony Beta that was consistently 2%-3% too fast. It consistently read 2-3% higher than Quickload estimated. When I changed to a CED M2, my velocities immediately started matching within 1% or closer to the estimates!

    AJ
     
  12. boomtube

    boomtube Well-Known Member

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    "
    The first sign of excessive pressure is...
    ...flattened primers? Then ejector marks? Then sticky bolt?"

    Those are the usual major signs but they don't give us the courtesy of showing up in predictable sequence. So...we just check for them all and note it when one shows up. What we do with that note depends a whole lot on how smart we are.
     
  13. buckbrush

    buckbrush Well-Known Member

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    Wow.

    A lot of great info here. Since my load is roughly 50 fps less than what Berger calls for and I am 1.6 gr hotter than their max load any thoughts on how much higher I can go?

    Berger calls for 66.4 gr of Retumbo yielding 2849 fps. I just checked my load data and I am at 68.0 gr of Retumbo getting right around 2800 fps. I worked up from 65 grains and the groups keep tightening up as the load gets hotter.

    Thanks to all who replied.
     
  14. montana_native

    montana_native Well-Known Member

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    I am very interested in your findings. I am working on a 7 mag too. When I used Berger's max data (I was actually at 66.5 gr rather than 66.4 gr of Retumbo) I was 100 fps lower than what they claim. I too had no pressure signs and am using CCI 250 primers.