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over pressure/under gas issue with new upper


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  • over pressure/under gas issue with new upper

    Just put together a new 24" bull barrel upper. Has rifle length gas system with standard lo-pro block. Took it the range today to sight in and had some issues with it. I got it on paper with Remington 55gr fmj and it did fine. I then switched to some hand loads to zero and work up a load for it. It short stroked every hand load I put through it. Some times it would eject the spent case and some times it would not. It would never cycle the bolt back far enough to grab a new round from the mag. Even when I worked up to max charges it would still do this.

    The load work up was Rem brass, XBR and 75gr HPBT. Even when at 23.8gr, I still had to manually load every round. Also, 23.8gr was the only charge that shot good, but I started to get ejector marks on the brass at 23.5gr. Every other .223 I have likes this combo somewhere between 23.5 and 23.8gr without any pressure signs. This is the only barrel I have that has a Wylde chamber if that matters.

    Will an adjustable gas block add more gas to cycle the action while decreasing the pressure?

    Any help would be great.


  • #2
    Your gas block is linef up properly? You removed it to check?


    • #3
      Since you just put on a gas block, and you have gas problems? That's where I'd be looking.

      You said it shot fine with Rem. 55s. What does that mean? Cycled from the magazine fine? Does any ammo work firing one round from the mag and it locks open? Where did it eject brass to? 1 0'clock? 4 o'clock?

      Whose brand barrel and gas block? Did you check the headspace with the bolt you're using? Is it a new BCG? Are the bolts on the key staked properly? Are you sure it's short stroking (not enough gas) or is it cycling (too much gas) too fast to pick up a round?

      If you're undergassed it sounds like the port in the barrel is too small so no, an AGB isn't going to add gas to make it cycle.

      Do you have a tool to measure the headspace of your fired Remington cases? What does that compare to your reloaded brass? Was it FL sized? New or fired in another rifle? Do you know the distance to the lands with the 75s? What's the OAL?


      • #4
        Originally posted by Southwind View Post

        Will an adjustable gas block add more gas to cycle the action while decreasing the pressure?
        No. An adjustable gas block can only restrict the amount of gas getting to your bolt carrier. It can't give more gas, and it has nothing to do with decreasing case pressure.

        Sounds to me like something is wonky with your setup or your load. If it cycles Remington 55gr, it should cycle that 8208 load just fine.


        • #5
          What lower did you use. Standard buffer and springs?