Looking for pressure signs and effect on gun

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  • 1911man
    Warrior
    • May 2015
    • 482

    Looking for pressure signs and effect on gun

    So some of you may have seen my last thread on my CFE 223 chrono numbers. I also had a thread earlier about factory hornady Amax showing pressure signs in my rifle. Based on my own thoughts and the advice of others on this board I decided to ignore the signs and keep shooting those factory loads anyway.

    My question is what are the signs that should actually scare you? and what are the results going to be of those signs? I have some factory hornady brass with super flat primers and even had one pierced primer. Now on my CFE 223 loads I am working up pretty high and I am not seeing these signs. Why should I be concerned with those loads over the factory hornady loads?

    Attached are some pictures from my most recent trip out. I have 10 rounds of 31.5 CFE, 10 rounds 31.8 CFE, 10 rounds of 32.1 CFE, and 10 rounds factory hornady amax in the box flipped over so you can see the primers. What do you guys see here? What I see is no flattening of the primers on 31.5 and 31.8 ( one primer in 31.8 was slightly edged). I then see the primers on the 32.1 slightly flattening. I also see that the stamp is a little more worn on the case head but these cases have been reloaded twice compared to the new hornady cases. Is there any ejector swiping? The craters look about the same throughout. I went ahead and punched out the primers on the cases that looked the most suspect and took pictures of them. The hornady primers are really flat, much more flat than any of the CFE 223 primers.

    Am I missing anything? What am I risking if I keep going up in charge on the CFE 223? I would really like to see what 32.4 grains and maybe even 32.7 grains would yield in terms of velocity. I am also not seeing any big spikes in velocity as I have gun up so far.

    Thoughts?
    Attached Files
  • Doon
    Bloodstained
    • Jan 2015
    • 81

    #2
    Are they ejector marks on your brass, if so I would back off.

    Comment

    • 1911man
      Warrior
      • May 2015
      • 482

      #3
      I have extractor marks on the brass but no ejector marks. The extractor is kind of gauging the rim of my brass, I am guessing I need to tune it to prevent this?

      Comment

      • rasp65
        Warrior
        • Mar 2011
        • 660

        #4
        1911 One of the things that can cause primer flattening is if the case is sized too much the fireing pin pushes the cartridge forward off the bolt face. When the primer ignites the charge it is then pushed back against the bolt face before the case fully expands to the chamber dimensions. The resulting case will have a very flat primer. Factory ammo is made to fit any chamber that is head stamped for the cartridge. As a handloader you set the dies so you size the brass only enough to allow proper function in YOUR firearm. As Doon said check for ejector marks also brass flow into the ejector recess. You might try filing off the sharp edges of your extractor that will help. I know over the years I have tried to clean up all the areas of the rifle that leave marks on the brass. It is much better that it was originally but it still leaves marks, it is the nature of the beast.

        Comment

        • LRRPF52
          Super Moderator
          • Sep 2014
          • 8569

          #5
          Gas guns need some play between the bolt lock up with the extension, we typically see slight flattening on primers on some guns, and none on others.

          Keep in mind that the working pressure of the Grendel is about 50,000psi, which is well below the point you would see primer flattening from excessive pressure.

          Additionally, primer flattening is not a reliable method for determining pressure, especially across a range of different primer types.

          Your chronograph is your best indicator of pressure, compared against published loads.
          NRA Basic, Pistol, Rifle, Shotgun, RSO

          CCW, CQM, DM, Long Range Rifle Instructor

          6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

          www.AR15buildbox.com

          Comment

          • Klem
            Chieftain
            • Aug 2013
            • 3509

            #6
            Another sign of overpressure is when the brass extrudes slightly into the extractor gap - that area of the bolt head which is not supporting the rim. This is not immediately noticeable until you resize the case and drop it into a rifle gauge. If it drops in but gets hung up at the rim run your finger around and you will feel a slightly raised bump. You can get rid of this bump by spinning the offending cases in a drill press while shaving it down with a file. You don't want to make a habit of doing this however.

            The trouble with overpressure is that there might not be any indicators until something breaks. As you say, primer cups are different metals and thicknesses so comparing what happens to them is fraught.

            Given Quickload is notoriously conservative I use it for determining max loads but always work up. This might sound a bit daft but the first round in a batch approaching peak pressure is fired from the hip...just in case. I trust Quickload's peak pressures more than their predicted velocities. I also record chrono readings and match that with what other posters are getting to determine what is the ballpark highest load, then work back from there to find the most accurate load.

            I guess it depends what your definition of safety is and then weighing that against what those extra few feet-per-second is worth.

            Comment

            • 1911man
              Warrior
              • May 2015
              • 482

              #7
              Thanks for the input guys.

              Comment

              • JASmith
                Chieftain
                • Sep 2014
                • 1620

                #8
                I did a fair bit of research into the mechanics of case head expansion coupled with a few tests and found some interesting things.

                I could not detect expansion of Hornady brass at Grendel pressures. Later, I learned that the yield strength of strain-hardened cartridge brass is frequently well above 50,000 psi.

                This brings one to the bottom line conclusion that reading brass for pressure might work for cartridges rated for 55,000 to 65,000 psi.

                Gas gun mechanics make effective use of brass abuse even more challenging because any visible expansion near the base is generally caused by early bolt unlock.

                Marks on the base are somewhat more viable because these appear where slight irregularities on the bolt face cause local stress concentration and allow creating visible marks with pressures below the nominal yield strength. The challenge here is that a pressure inference based on the marks becomes more of an art than a science because the markings are frequently unique to the rifle.

                The techniques can also work for the Grendel if one understands that seeing bonafide signs of pressure in the brass means that the pressures are already dangerously high and that one needs to back off a fair bit or make other adjustments.

                If factory loads show these signs, then one needs to check to see if the bullet engages the lands when going into battery. Engaging the lands before the shot can add several thousand psi to the peak pressure. That suggests trying a different factory load with the same bullet. The results would then tell one whether to approach the rifle maker or the ammunition manufacturer for assistance or corrective action.
                shootersnotes.com

                "To those who have fought and almost died for it, freedom has a flavor the protected will never know."
                -- Author Unknown

                "If at first you do succeed, try not to look astonished!" -- Milton Berle

                Comment

                • lwminton
                  Warrior
                  • Nov 2014
                  • 143

                  #9
                  Originally posted by LRRPF52 View Post
                  Gas guns need some play between the bolt lock up with the extension, we typically see slight flattening on primers on some guns, and none on others.

                  Keep in mind that the working pressure of the Grendel is about 50,000psi, which is well below the point you would see primer flattening from excessive pressure.

                  Additionally, primer flattening is not a reliable method for determining pressure, especially across a range of different primer types.

                  Your chronograph is your best indicator of pressure, compared against published loads.
                  What do you look for in chrono results to indicate excess pressure.

                  Comment

                  • LRRPF52
                    Super Moderator
                    • Sep 2014
                    • 8569

                    #10
                    Originally posted by lwminton View Post
                    What do you look for in chrono results to indicate excess pressure.
                    Velocity way outside what you would expect from published loads with the same barrel length.

                    Excursions in velocity that exceed the trend you see in charge weight incremental increases. Example, I normally see about 18-25fps with .3gr of CFE under a 123gr, all of a sudden, I see a spike of 40-60fps or more with the same charge weight increase. Time to stop and call the ladder test limit.

                    Faster speeds are generally synonymous with more pressure.
                    NRA Basic, Pistol, Rifle, Shotgun, RSO

                    CCW, CQM, DM, Long Range Rifle Instructor

                    6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                    www.AR15buildbox.com

                    Comment

                    • lwminton
                      Warrior
                      • Nov 2014
                      • 143

                      #11
                      Originally posted by LRRPF52 View Post
                      Velocity way outside what you would expect from published loads with the same barrel length.

                      Excursions in velocity that exceed the trend you see in charge weight incremental increases. Example, I normally see about 18-25fps with .3gr of CFE under a 123gr, all of a sudden, I see a spike of 40-60fps or more with the same charge weight increase. Time to stop and call the ladder test limit.

                      Faster speeds are generally synonymous with more pressure.
                      If you examine primers at that point, do you see confirmation - always or not always

                      Comment

                      • JASmith
                        Chieftain
                        • Sep 2014
                        • 1620

                        #12
                        Originally posted by lwminton View Post
                        If you examine primers at that point, do you see confirmation - always or not always
                        You should not see significant pressure flattening unless the pressures are above 55,0000 psi.

                        Confusing matters more, not all primers are bullt the same way, so there could be differences of several thiusand psi for the onset of noticeable flattening.

                        We can be reasonably sure, however, that flattened primers suggest that the pressure is higher than recommended for the Grendel.
                        shootersnotes.com

                        "To those who have fought and almost died for it, freedom has a flavor the protected will never know."
                        -- Author Unknown

                        "If at first you do succeed, try not to look astonished!" -- Milton Berle

                        Comment

                        • LRRPF52
                          Super Moderator
                          • Sep 2014
                          • 8569

                          #13
                          Originally posted by lwminton View Post
                          If you examine primers at that point, do you see confirmation - always or not always
                          You will often see flattened primers in gas guns due to the extra headspace slop needed to keep them reliable.

                          A lot of my factory ammo shows flattened primers, but speeds well within expectations. What should I assign more weight to?

                          * Actual muzzle velocity?

                          * Flattened primers?

                          Since I understand that gas guns have slop, and the speed is right where it should be, the flattened primers are noted, but not indicative of excessive pressure in that case.
                          NRA Basic, Pistol, Rifle, Shotgun, RSO

                          CCW, CQM, DM, Long Range Rifle Instructor

                          6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                          www.AR15buildbox.com

                          Comment

                          • JASmith
                            Chieftain
                            • Sep 2014
                            • 1620

                            #14
                            Originally posted by LRRPF52 View Post
                            You will often see flattened primers in gas guns due to the extra headspace slop needed to keep them reliable...
                            Point taken ... Earlier post refers to bolts and single shots.
                            shootersnotes.com

                            "To those who have fought and almost died for it, freedom has a flavor the protected will never know."
                            -- Author Unknown

                            "If at first you do succeed, try not to look astonished!" -- Milton Berle

                            Comment

                            • 1911man
                              Warrior
                              • May 2015
                              • 482

                              #15
                              Originally posted by LRRPF52 View Post
                              You will often see flattened primers in gas guns due to the extra headspace slop needed to keep them reliable.

                              A lot of my factory ammo shows flattened primers, but speeds well within expectations. What should I assign more weight to?

                              * Actual muzzle velocity?

                              * Flattened primers?

                              Since I understand that gas guns have slop, and the speed is right where it should be, the flattened primers are noted, but not indicative of excessive pressure in that case.
                              Ill second what LRRPF52 said. My Grendel is the first gas gun I have ever loaded for so it took me a while to learn what to look for. A good chronograph is probably the most important tool for measuring pressure in a gas gun. Also, this highlights the importance of working your way up in pressure. If the max is 28.5 grains dont start at 28.3. If you work your way up you will get a feel for how much increase in velocity you should be seeing as you increase the charge. Now combine that with signs in the brass and you have a good formula. Another thing I have noticed is felt recoil can be a good indicator. For example when I first starting shooting the Grendel the Factory Hornday Amax load was different. It was much softer recoil, no flattened primers, and the velocity was much more consistent. The first time I shot a box of their new formula the recoil was much harder and I should have taken note of it. After five boxes of the new stuff I blew an extractor and I haven't shot another box of factory amax. Also, the accuracy went down the toilet with the new formula. The point is dont just look at one indicator.
                              Last edited by 1911man; 02-06-2016, 02:31 AM. Reason: Spelling

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