Growing chamber?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • Sticks
    Chieftain
    • Dec 2016
    • 1922

    Growing chamber?

    Upper is a PF Neptune VIII, 18" Barlitien barrel, PF NiB BCG.

    I always take a few random samples of my brass when I get back from shooting to examine them before sorting. Aside from what seems like excessive scuffing. My brass typically measures 1.221 for Factory ammo, 1x or 2x fired reloads FL sized back to 1.117.

    This last round the brass measured 1.225, both new ammo and reloaded. I verified against some other 1x fired brass that has not been molested yet and they still measure 1.221.

    If I can keep consistent on my end (final firing position) I am still getting .4 moa groups.

    I doubt this is normal, I have never read anything like this as a problem before.

    Any place in particular that I should be looking for a start?
    Sticks

    Catchy sig line here.
  • grayfox
    Chieftain
    • Jan 2017
    • 4295

    #2
    Couple of random thoughts:
    Maybe chamber temps have an effect? Has cycling timing changed?
    My fired AR brass seems to range from 1.222 to 1.226 routinely, for either AR I pick.
    Honestly I hadn't given it much thought.
    Next couple of times I shoot them I'll double check... I'm shooting a couple ARs now in Grrr.
    Reason I've checked in the past is AR brass comes out a bit longer for me than my Howa brass.
    1.222+ etc vs 1.218 or so, as-fired (speaking from memory).
    "Down the floor, out the door, Go Brandon Go!!!!!"

    Comment

    • Sticks
      Chieftain
      • Dec 2016
      • 1922

      #3
      Originally posted by grayfox View Post
      Couple of random thoughts:
      Maybe chamber temps have an effect? Has cycling timing changed?
      My fired AR brass seems to range from 1.222 to 1.226 routinely, for either AR I pick.
      Honestly I hadn't given it much thought.
      Next couple of times I shoot them I'll double check... I'm shooting a couple ARs now in Grrr.
      Chamber temps, and ambient have actually been cooler. My cyclic rate is slowing down a bit, but the rifle seems to be wanting an adjustment of the gas block. Starting to run a bit fast and tossing the brass forward.

      Reason I've checked in the past is AR brass comes out a bit longer for me than my Howa brass.
      1.222+ etc vs 1.218 or so, as-fired (speaking from memory).
      3 diffferent Howa's (The Horde) and they all measure 1.213 on average (+/- .0005). I have to keep them separate. No way am I gong to size that far back for my AR. Waste of brass life.
      Sticks

      Catchy sig line here.

      Comment

      • grayfox
        Chieftain
        • Jan 2017
        • 4295

        #4
        Same for me on the howa, I use 2 separate sizing dies - 1 for the HB - other for the ARs, so I don't have to adjust back n forth...
        Possibly if the cycle rate is slowing down then more stretch-time on the brass before ejection, plus it might be somewhat warmer so more ductile (maybe some, don't know how much but we're talking 0.001's, so...). Just a thought.
        "Down the floor, out the door, Go Brandon Go!!!!!"

        Comment

        • Sticks
          Chieftain
          • Dec 2016
          • 1922

          #5
          I should have less cryptic. My cyclic rate, not the rifle, is slower, meaning I am not taking shots as fast, and taking longer breaks between strings of 5.

          The Rifle however seems to be running faster kicking the brass off the deflector and forward.
          Sticks

          Catchy sig line here.

          Comment

          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #6
            Faster cyclic rate from the action is the culprit in longer shoulder datum for fired cases because there is less time to heat sink into the chamber, and the case is being extracted earlier.
            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

            • Sticks
              Chieftain
              • Dec 2016
              • 1922

              #7
              Thank you LRRPPF52. I will go through the GB adjustment again, then verify results.
              Sticks

              Catchy sig line here.

              Comment

              • grayfox
                Chieftain
                • Jan 2017
                • 4295

                #8
                Guess I had it backwards, thanks '52, glad to learn.
                Sticks on the other point above (howa vs AR shoulder lengths) today I measured several of my howa's and one set from AR, the howa's came out 1.2165-1.2175 after firing and the AR was 1.2205-1.2210, so need to update my memory cells...
                "Down the floor, out the door, Go Brandon Go!!!!!"

                Comment

                • Sticks
                  Chieftain
                  • Dec 2016
                  • 1922

                  #9
                  Thank you grayfox.
                  Sticks

                  Catchy sig line here.

                  Comment

                  • LRRPF52
                    Super Moderator
                    • Sep 2014
                    • 8569

                    #10
                    Maybe we should change the thread title to "Brass growth in Semi auto vs bolt gun" and put it in reloading section...

                    An actual growing chamber is a major problem where the tennon is stretching or the chamber walls are expanding in a poorly-designed or manufactured containment vessel.

                    White Oak developed a barrel extension to deal with this for Service Rifle shooters who are pushing 90gr VLDs hard.

                    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

                    • Sticks
                      Chieftain
                      • Dec 2016
                      • 1922

                      #11
                      Originally posted by LRRPF52 View Post
                      Maybe we should change the thread title to "Brass growth in Semi auto vs bolt gun" and put it in reloading section...
                      I keep track of my brass after shooting. When I get home and am sorting them out after a session, I take a few random cases and give them a good look over and take some measurements. This is when I noticed that my brass in that rifle is starting to get longer. Red flag for me, I am wanting to find out why in case I have a serious issue developing.
                      Sticks

                      Catchy sig line here.

                      Comment

                      • ricsmall
                        Warrior
                        • Sep 2014
                        • 987

                        #12
                        52 is correct. Cyclic rate speeding up is the culprit. My guess is the rifle is smoothing out or breaking in, or the gas block adjustment is moving, or gas port is eroding (not likely unless high cyclic rate and high round count). Another explanation could be lack of escaping gas after a few hundred rounds due to carbon build up sealing off gas block and bolt tail.
                        Member since 2011, data lost in last hack attack

                        Comment

                        • Frontier Gear
                          Warrior
                          • Nov 2017
                          • 772

                          #13
                          Originally posted by ricsmall View Post
                          Another explanation could be lack of escaping gas after a few hundred rounds due to carbon build up sealing off gas block and bolt tail.
                          ^^^ +1 vote for the gas block leak. Ever install a gas block and shoot about 50 rounds then remove the gas block? It gives you a good idea of how well it was sealed.
                          Engineer, FFL and Pastor

                          Comment

                          • Texas
                            Chieftain
                            • Jun 2016
                            • 1230

                            #14
                            I agree with the gas block sealing and that should be varifiable by the shoulder being moved forward as well.

                            Comment

                            • Sticks
                              Chieftain
                              • Dec 2016
                              • 1922

                              #15
                              It's not a gas block leak. Not bedded, but it was sealed well, if crooked.
                              Sticks

                              Catchy sig line here.

                              Comment

                              Working...
                              X