Light Primer Strikes Problem

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  • keystone183
    Warrior
    • Mar 2013
    • 590

    Light Primer Strikes Problem

    Over the weekend I had trouble with light primer strikes. Was shooting several different types of ammo and the results were thus:

    - Hornady A-Max and SST factory loaded ammo = goes bang every time.
    - AA loaded 120 Noslers = goes bang every time
    - Wolf steel case = dimples only, no ignited primers in 5 rounds.
    - AA loaded 129 SST's = dimples only, no ignited primers in 8 rounds

    Both the AA loads were pretty old. Bought them at least a year and a half ago, probably 2.

    This was in two separate rifles, also. Two different triggers, hammers etc. One is running a PF bolt in a JP BCG with a Hiperfire trigger/hammer. The other is running a PF bolt in a Crosshill Tech BCG with a JP trigger/speed hammer, yellow springs. Anybody got any ideas?
  • LRRPF52
    Super Moderator
    • Sep 2014
    • 8569

    #2
    Full power hammer spring is the solution I think. The JP yellow spring is notorious for light primer strikes, especially in cold weather. The speed hammer helps, but you really need more momentum from the hammer. I like the brown AR10 hammer springs that come with the JP kit, but a full power hammer spring really will reliably ignite your primers, even in extreme cold.

    This is another reason to look at Geissele.
    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

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    • keystone183
      Warrior
      • Mar 2013
      • 590

      #3
      That is what i thought, too, but it should have been gtg on the hiperfire (at least according to their marketing). And it was cold, but not that cold....45 in Texas. What has me boogered is that there was no in between. Not a single ignition on two separate types of ammo, across two lowers, and 100% reliability for 3 other types across the same two. Seems improbable if it were just a problem of hammer fall energy? I have another lower with a mil spec parts kit i guess i'll slap on to see if that solves the problem.

      Comment

      • LRRPF52
        Super Moderator
        • Sep 2014
        • 8569

        #4
        Were the springs installed correctly? I'm used to running high volume in extreme cold, like -30 C, waaaaay below freezing. The only guns I have seen with FTFire are AK's in those conditions.
        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

        • keystone183
          Warrior
          • Mar 2013
          • 590

          #5
          Problem solved.... Slapped on another lower with a milspec parts kit in it. And, as Slappy would say......BANG BANG. I'll have to check which set of springs i have in the Hiperfire. I think it was the middle weight set, but not sure. i'll have to try the highest power and see if that helps. This is very disappointing, as i love that trigger other than this...

          Comment

          • keystone183
            Warrior
            • Mar 2013
            • 590

            #6
            Anybody have any insight in to what the difference might be in the primers in the two AA loadings?

            Comment

            • RangerRick
              Bloodstained
              • Sep 2014
              • 46

              #7
              A light primer strike can also indicate that the bolt isn't fully locked into battery with the carrier all the way forward.

              The 129 is a long bullet and the Wolf steel case may be too, or if the ogives may be fat. If these bullets are engaging the rifling and keeping the bolt from fully locking you can have high pressure problems.

              So getting a bigger hammer (spring) may not be the best solution to the problem!

              The AR is designed so that if the bolt is not locked with the carrier all the way forward, the primer can't get a good hit because the hammer hits the front edge of the slot in the bottom of the bolt carrier. That (hopefully) keeps rounds from firing with an unlocked bolt.

              To be extra safe I'd check the space between the front of your carrier and the barrel extension with the bolt closed without, then with one of the rounds that won't fire.

              With the chamber empty there is a small gap between the front of the carrier and the barrel extension. With a round in the chamber, the gap is a little wider, but should not be much wider.

              Also chamber the rounds that only get a primer dent and see if they are hard to extract. Look for rifling marks on the bullet after you extract them.

              If the carrier isn't all the way forward, the bolt isn't fully rotated and your bolt lugs may not be fully rotated behind the lugs in the barrel extension.

              Should the primer ignite with the light strike, this is at the very least not good for your bolt and at the worst, leaves the bolt unlocked when it fires.

              That last little bit of forward motion of the carrier is what causes the bolt to rotate. The bolt stops moving forward but the carrier keeps going forward.

              The cam pin sticking through the bolt rides in the slot at the top of the upper so the bolt can't rotate until the cam pin gets to the big open space in the front top of the upper by the gas tube.

              The diagonal cam pin slot in the carrier then causes the cam pin to rotate, and since it is sticking through the hole in the side of the bolt, it levers the bolt over causing it to rotate.

              The cam pin riding in the slot at the top of the upper keeps the bolt lugs lined up with the slots in the barrel extension until they slide through. It's why you have to extend the bolt all the way out in the carrier so you can put the assembled bolt and carrier in the back of the upper.

              If the bolt isn't extended, the rectangular top of the cam pin can't go in the slot at the top of the upper because it isn't top dead center on the carrier under the gas key.

              If you see a big difference between the space at the front of the carrier with and without a round in the chamber, you should check your head space and/or make sure the bullets aren't jammed in the rifling.

              If you have LBC 264, or other non Grendel spec chambers, or a Grendel chamber not reamed out enough (seems to happen somewhat frequently), you might get a bullet jammed in the lands.

              If you are using a 7.62x39 bolt in a barrel head spaced for a Grendel bolt or vice versa, you could have an unsafe situation.


              RR
              Last edited by RangerRick; 11-21-2014, 12:35 AM. Reason: typo

              Comment

              • RangerRick
                Bloodstained
                • Sep 2014
                • 46

                #8
                This is also why there is a forward assist. Whacking it can cause the carrier to slide the last little bit if the chamber is dirty or a round is bent, thus allowing the rifle to fire.

                Not a good idea, though, if all you are doing is pounding the bullet into the lands.


                RR

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