Page 1 of 4 123 ... LastLast
Results 1 to 20 of 80

Thread: Pressure signs

  1. #1
    Member Bullelkklr's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage Alaska
    Posts
    4,841

    Default Pressure signs

    I am reading an old reloading book by (1949) by Phillip Sharps. Complete Guide To Handloading.

    He goes into detail about head spacing and if I read it correctly, he craters my thoughts of what I always thought excessive pressure signs in my primers really is. Flattened primers or primers that are pushed out a little from the case he attributes to bad head spacing.

    I know that the book is old, but the physics are the same.

    What is everyone's thoughts on what is really happening when our primers are flat? (I haven't had this happen since my college days when I tried to make my 30.06 a 30.06 magnum).

    How do YOU know when you have excessive pressure signs?


    I was a bit worried about running 73.5 grains of RL19, 225 grain Barnes TTSX, WLRM primers, OAL= 3.3375 in my .338wm ...but it shoots fine and I can't see any excessive pressure signs. When you pull the trigger it "feels" like a heavy load. I started at 69 and worked up 5 round tests at .5 gr steps. The 73.5 had the best grouping, I didn't have my chrono with me at the time. The Griz I shot in the sternum at 70 yards did not argue either.

  2. #2
    Moderator
    Join Date
    Jan 2005
    Location
    Midwest
    Posts
    4,431

    Default

    He's right of course but the thing to do is load your ammo in cases fired in your chamber and don't size them fully and push the shoulder back. This creates that little bit of excess headspace that can allow the primer to move back at ignition. If the case is touching at the headspace datum, it will not have slop to move in the chamber so the bolt head will be in contact with the case head. This can also be caused by primer pockets that are deeper than spec and when seated to the bottom they are a bit too much below the case head.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  3. #3
    Member Bullelkklr's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage Alaska
    Posts
    4,841

    Default

    I always just neck size my brass and all brass is kept separated per rifle. I started with a Lee load all in 1983 for my 22.250.............

    What are the first signs of pressure then, assuming that it is a second round reload neck sized from the same rifle? I always assumed that it was a hard(er) working bolt upon extraction and/or flattened primers. None of my heavy loads since about 1994 have had any issues.

    I even got that ole 30.06 savage 110E "magnum" shooting pretty good groups again after I found a little bulge in the tip of the barrel and whacked that off and started lengthening my loads to be as close to the lands as I can get them and still get em in/out of the mag.

  4. #4
    Member
    Join Date
    Feb 2008
    Location
    Fairbanks
    Posts
    301

    Default

    If getting flatened primers on a starting loads, than they may be due to headspace.

    If later in load development I got flatened primers after starting loads had primers still flush with the case, I would call it a pressure sign. That said personally I do not think slightly flatened primers are a major pressure sign, given that most factory loads have slightly flatened primers, they are one of many things to look at though.

  5. #5
    Member
    Join Date
    Aug 2007
    Location
    Eureka MT
    Posts
    3,048

    Default

    Sticky bolt lift is a sure sign that you are over the top. Flattened primers and cratered primers can be signs of high pressure as well as higher velocity than expected but other things can cause these effects as well.

  6. #6
    Moderator
    Join Date
    Jan 2005
    Location
    Midwest
    Posts
    4,431

    Default

    I believe the most reliable way to determine over pressure to measure the case webb expansion before and after firing. 60,000 psi will generally expand case webb diameter .0008" to .0010". This should be done with brass that has been fire-formed at about 75% pressure peak then make measurements. The maximum allowable expansion for a bolt action rifle should be no more than .0010". You need a good mike.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  7. #7
    Member
    Join Date
    Jan 2008
    Location
    Anchorage
    Posts
    895

    Default

    What is the "Webb" of a case. I have never heard that used before in relation to brass.

  8. #8
    Member
    Join Date
    Feb 2007
    Location
    Los Anchorage
    Posts
    481

    Default

    when I start loading for a rifle I usually start at the bottom of the scale with a cheap bullet usually sierra. I break the barrel with these ect. Once those are fire formed to the chamber I measure the case with the hornady brass gauge "for lack of better terms". I then set back the shoulder .020. From there is where I really start loading for the rifle. I don't measure case web, but it is something that I might start doing. All my rifles are hunting, but I try to get every bit I can out of them.

  9. #9
    Member
    Join Date
    Apr 2006
    Location
    SwampView AK, Overlooking Mt. Mckinley and Points Beyond.
    Posts
    8,816

    Default

    I operate on the premise that the best way to safe pressures is with a chronograph. Velocities should be in keeping with

    expected velocities of the cartridge for that bullet weight.

    Absence of pressure signs doesn't assure safe pressures, and the presence of pressure signs very likely indicates way more than a little too much.

    With a chronograph, higher than normal velocity can be a pressure sign that is more accurate than the others for indicating unsafe pressure.

    For example, if you're gittin 300 Mag speeds out of a 30-06, you are over-pressure, even if you don't see Other, pressure signs.

    I've not had lots of experiences with pressure signs, but hopefully doin it like that, the way I've outlined, will keep it that way.

    That's about all I use my chrono for. To keep my loads safe, not to wring the last fps in my loads.

    Smitty of the North
    Walk Slow, and Drink a Lotta Water.
    Has it ever occurred to you, that Nothing ever occurs to God? Adrien Rodgers.
    You can't out-give God.

  10. #10
    Moderator Paul H's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    5,594

    Default

    Quote Originally Posted by Smitty of the North View Post
    I operate on the premise that the best way to safe pressures is with a chronograph. Velocities should be in keeping with

    expected velocities of the cartridge for that bullet weight.

    Absence of pressure signs doesn't assure safe pressures, and the presence of pressure signs very likely indicates way more than a little too much.

    With a chronograph, higher than normal velocity can be a pressure sign that is more accurate than the others for indicating unsafe pressure.

    For example, if you're gittin 300 Mag speeds out of a 30-06, you are over-pressure, even if you don't see Other, pressure signs.

    I've not had lots of experiences with pressure signs, but hopefully doin it like that, the way I've outlined, will keep it that way.

    That's about all I use my chrono for. To keep my loads safe, not to wring the last fps in my loads.

    Smitty of the North
    Extremely well put, there are no free lunches when it comes to velocity and "pressure signs" are really over-pressure signs.

    The problem with the conventional suggestion of looking for pressure signs then backing off is often those signs don't show up until about 73,000 psi, well over the 65,000 psi limit. The published data correlated with a chrono is the best approach. If you're really concerned, invest in a piezio electric pressure trace strain gauge unit.
    Those that are successful in Alaska are those who are flexible, and allow the reality of life in Alaska to shape their dreams, vs. trying to force their dreams on the reality of Alaska.

    If you have a tenuous grasp of reality, Alaska is not for you.

  11. #11

    Default

    there is a quick and dirty way of headspacing
    you take a spent primer and just barely seat it in an empty case
    chamber the case, measure the primer protrusion and you have head space

    as for signs of pressure, you have primer pop from low loads, you have it from excessive loads, bad head space etc.
    so, YOU best know your signs and how your gun works, as there isn't ONE cause, there are a few.

  12. #12
    Member
    Join Date
    Aug 2007
    Location
    Eureka MT
    Posts
    3,048

    Default

    Murphy
    I suspect your method is quite accurate but I'm a little unclear as to proceedure. You fire form a 75% load and measure it. I assume you then neck size only and fire a full load and remeasure with .010 being the upper limit. I also assume the measuring point to be at the fattest point of the case just ahead of the web of the case. Am I thinking correctly?

  13. #13
    Moderator
    Join Date
    Jan 2005
    Location
    Midwest
    Posts
    4,431

    Default

    No. Measure the Webb and max is .001". Not .010". You need a good precision micrometer with .0001" accuracy.
    The bulge in the case body is from chamber size vs brass diameter. Quite common. Think of the thrust of the pressure pushing the brass plug back against the bolt head. It is bulging that solid brass billet in the base of the case.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  14. #14
    Moderator
    Join Date
    Jan 2005
    Location
    Midwest
    Posts
    4,431

    Default

    Quote Originally Posted by Shadow7D View Post
    there is a quick and dirty way of headspacing
    you take a spent primer and just barely seat it in an empty case
    chamber the case, measure the primer protrusion and you have head space

    as for signs of pressure, you have primer pop from low loads, you have it from excessive loads, bad head space etc.
    so, YOU best know your signs and how your gun works, as there isn't ONE cause, there are a few.
    Good tip. Very true.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  15. #15
    Moderator
    Join Date
    Jan 2005
    Location
    Midwest
    Posts
    4,431

    Default

    Quote Originally Posted by Daved View Post
    What is the "Webb" of a case. I have never heard that used before in relation to brass.
    That solid billet of brass where the case head and primer hole are. Below the hollow body. It's about .220" thick on most rifles. It is the gasket that keeps gas from blowing out the base of the brass. It starts to expand at about 50,000 psi.
    It is similar to the copper slug used in copper crusher systems. (CUP). There is some predictability in expansion of this "solid" under pressure.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  16. #16
    Member
    Join Date
    Aug 2007
    Location
    Eureka MT
    Posts
    3,048

    Default

    Ok,got it. It was late when I read your post. I think I need to pay more attention to the decimal point. I have good mics that will measure .0001. Does this expansion continue in an even progression as the case is fired again and again or do I need to start with new brass?

  17. #17
    Member ekberger's Avatar
    Join Date
    Oct 2009
    Location
    Indiana, only because that's where the check came from...
    Posts
    150

    Default Techniques for measuring the case web

    As pointed out by Murphy, I use case webb measurements when I suspect that I may need to pay attention to pressure signs. You need blade micrometer and the ability to accurately measure the same spot with some consistency. This URL has an article on one method that I find works for me to get consistent measurements (see Base Diameter). http://riflemansjournal.blogspot.com...ring-case.html

  18. #18
    Member
    Join Date
    Aug 2007
    Location
    Eureka MT
    Posts
    3,048

    Default

    ekberger
    Thanks for the link. It all makes perfect sense now that I think about it for a bit. Simple enough to do as well as probably being about the best way to indicate pressure without very expensive equiptment. Is there much variation from brand to brand of brass as in one brand is harder than another and will give less expansion for a given pressure? On belted cases can you measure the belt?

  19. #19
    Member ekberger's Avatar
    Join Date
    Oct 2009
    Location
    Indiana, only because that's where the check came from...
    Posts
    150

    Default

    Thanks, "Simple enough" yes, but consistency and accuracy are the key. I don't want to imply in this next statement that it pertains to you, however, as a general comment...one needs to be able to use a measuring instrument in the same way each time and take that measurement from the same place on the brass. It's really a skill and I know in my own case a machinist friend drilled that into me. As pointed out, a blade micrometer is designed for this type of measurement. When your reading said instrument down to the 0.0001 or fourth decimal place it takes a little practice, a digital instrument makes that a bit easier, however, it too has the same requirements.

    To your question, the answer is yes hardness does vary between brands and at times lots, that's just the nature of the beast. However, at the webb the brass is much thicker than what you find as you go up the case wall. Your question is relevant however, I don't have have an answer for you. The thing you're trying to do is measure the relative case webb expansion on your individual rounds from your reference point prior to firing. If you have an overpressure situation it should be noted. I really don't think this is brass dependent, however, the only way to test this would be with a controlled experiment comparing the different brands with a statistically relevant sample size. That would be a lot of work.

    On belted cases you measure just above the belt. If you cut one of these cases longitudinally, you'll see the where this is but it's not necessary.

  20. #20
    Member ekberger's Avatar
    Join Date
    Oct 2009
    Location
    Indiana, only because that's where the check came from...
    Posts
    150

    Default

    Another reference for how to take these measurements can be found in Glen Zedikers's book, "Handloading for Competition, Making the Target Bigger". The discussion in the book begins on page 246. A comment that I think pertains to your question is "A shooter needs to needs to know what is normal for his rifle and brass, and that he's accurately able to measure it". You want to be able to compare a new load to the expansion after the first and subsequent firings.

Page 1 of 4 123 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •