Pressure signs?

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  • Pressure signs?

    I'm trying to figure out why I have primers that are flattening out. Usually, I consider this to be from excess pressure, or excess headspace. As I mic the rounds after firing them, and only set the shoulder back about .002 for each rifle, I don't think it is excess headspace.

    I'm using 30.4 grains of AA2520 with a 123 grain Lapua Scenar. Brass is trimmed after every sizing before loading, so I know I'm not jamming the neck into the throat.

    I have cleaned the rifles with Sweet's 7.62, used a brush, cleaned again to insure I have all carbon, copper, and powder fouling out of the barrels.

    The bullet was seated to 2.260, but unfired rounds came out of the rifle with the rifling engraved onto the bullet. So, I have seated the bullet deeper into the case. I check bullet depth by using candle soot on dummy rounds to find the right depth for the bullet.

    Both my AA Shilen barrel, and my Lothar Walther barrel show the same primer flattening. I switched to AA2520 because my load of W748 showed the same thing, even with velocity at 2430 fps out of my 19.5 inch barrel (30.3 grains).

    I'm using Lapua cases, CCI450 primers, Lapua 123 grain scenar bullets. Velocity through the 19.5 inch AA Shilen barrel is 2482, 2498, 2502, 2505 fps. The factory load is over 2600 with a higher powder charge. Velocity through the 18 inch Lothar Walther barrel is about 45 fps lower.

    Primer pockets remain really tight, and brass loss from cracked necks and other causes is the same as it has always been. The brass has been reloaded a number of times, and necks have been annealed.

    My velocity levels indicate that I am right where I should be with that powder charge. If I were over pressure, I would at least think I would be getting more velocity. I load for accuracy, not velocity if that matters.

    Any ideas on what is happening? Maybe some minor primer flattening is normal, and I shouldn't worry about it. The primers aren't completely flat, none are pierced, none flow back into the firing pin hole.

  • #2
    please post pictures of the flattened primers.

    Comment

    • bwaites
      Moderator
      • Mar 2011
      • 4445

      #3
      Right or wrong, I have completely disregarded minor primer flattening signs in the AR, and particularly the Grendel, as meaning anything significant.

      I have seen factory 5.56, .223, Grendel, and .308 all show primers that I would consider dangerous in a bolt gun. I've seen cratering, sharpened edges, flattening, etc. in loads that I loaded that were at minimum or only slightly above that.

      If they aren't filling the primer pocket, there is no piercing, and no flow back, then I just deal with it and shrug my shoulders.

      That said, 2520 has some interesting properties, and many of us are somewhat suspicious of it when it comes to temperature changes, which we often see in the spring.

      Comment


      • #4
        1. I don't have the ability to load photos.
        2. This is my first time using 2520 in the Grendel. The same thing happened with my load of W748, and velocity was only around 2430 fps with the same bullet.
        3. My friend Infidel470 says that as the summer warms up, he continually reduces his load of 2520 down toward 30 grains. If it gets really hot (over 90F) he would consider even lower. My loads probably won't see the end of june though, and that will be in the Puget Sound area of Washington state where temperatures would top out around 70F. So I'm thinking that this load should be OK.
        4. My COAL had to be set back quite a bit more than with the last lot of 123 Scenars so that I wouldn't have the bullet jammed into the rifling. The COAL is now around 2.250 nominal. At 2.260 I could clearly see the lands engraved on the bullets of unfired rounds, so I set them back.
        5. I realize that bullets intruding into the powder space increases pressures somewhat. But given the choices of either bullets jammed into the rifling VS bullets intruding into the powder space, I'll avoid the excess pressure spikes associated with bullets jammed into the rifling in favor of seating the bullets with some jump to the start of the rifling.
        6. I haven't had any pierced primers, blown primers, primers flowing into the firing pin hole, completely flattened primers, or primers with the circular flow marks on them.

        Wouldn't the velocity, and the consistency of the velocity indicate that I am within normal pressure limits? I would think that excess pressures would be shown by rather radical spikes in velocity, or quite large swings in the velocity readings.

        Comment


        • #5
          The slight amount of flattening you describe is normal, I have noted it with every factory rnd....AA-123, wolf-120&123, and Hornady fired thru my AA/Shilen. No reflection on you I just prefer pictures to ensure we prevent misunderstandings.... fire away and enjoy!

          Comment


          • #6
            Recently, when I went a half grain step or two too far, my velocity SDs tightened up to only 3 or 4. They're usually in the low teens when I'm getting my best groups. As the others said, there's going to be some flattening. I don't worry as long as there is some shoulder left on the primer.

            Hoot

            Comment


            • #7
              There is some shoulder left on the primer, but not much. I have had primers come out of other rifles when doing load development that actually had a burr where the shoulder used to be. Needless to say, I pulled the remaining bullets, and went with the lower powder charges. These primers are no where close to being that flattened.

              Because I like to err on the side of caution, I thought I should at least ask for some other input. In addition to the opinions offered in this thread, the things that would cause me to be less worried about the possibility of excess pressure are:
              1. The velocity is well within what would be considered "reasonable" for this load at 2500 FPS out of a 19.5 inch Shilen barrel from AA. The factory load with this powder listed in the printout I have from AA shows a velocity of 2630 with 30.7 grains.
              2. Velocity doesn't show any unusual "spikes". My extreme spread for velocity is 23 fps, so that isn't too bad.
              3. Primer pockets don't show any unusual loosening, no primers pierced, flowing back into the firing pin hole, or popped out of the primer pocket.

              Thanks very much for the help. I appreciate the input. This is one of the reasons I enjoy this forum so much. Almost everyone on this site is helpful, while on some boards people seem to act like they are just lurking and waiting to denigrate other people on the site. Thanks again!

              Comment

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