COAL and "Free" Velocity Gains

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  • BluntForceTrauma
    Administrator
    • Feb 2011
    • 3897

    COAL and "Free" Velocity Gains

    There are some who claim that increasing the COAL (Cartridge Over All Length) in an AR from the standard 2.260 to 2.300 will net an increase in velocity. Technically, it's true. No less a ballistics authority than Bryan Litz would agree — up to a point.

    In Litz’s article on the Berger Bullets website he states, “In fact, the extra powder you can add to a cartridge with the bullet seated long will allow you to achieve greater velocity at the same pressure than a cartridge with a bullet seated short.”

    This is all well-and-good as we seek “free” velocity gains, but the amount of difference in COAL in two otherwise equal loadings is key. For example, the Accurate Powder website FAQ #23 states: "However, [1.0mm] in the case of a rifle caliber, which is much longer, will have a very small to insignificant effect.”

    In the case of an AR, the difference between a COAL of 2.260 and 2.300 is, yes, 1.0mm.

    Now, what I found really interesting in a recent announcement about the ABM line of ammunition developed by Litz himself is the minimal gain in velocity from two otherwise identical loads having differing COALs.

    Litz has two new .308 Win. loadings, one at 2.950 and the other at 2.80 — difference of 0.150 or 3.8mm.

    How much velocity does he gain from loading the one almost 4mm longer than the other?

    The longer gets 2628 fps from a 24” barrel and the shorter gets 2608 — difference of 20 fps.

    What to conclude? If you can load long within your magazine constraints in the hope of gaining “free” velocity, do so — every little bit helps — but don’t knock yourself out. Unless 20 fps is meaningful to you, you’re largely wasting your time buying expensive magazines that allow for longer loading or cutting the fronts out of magazines. Those seeking to turn a mediocre-performing cartridge into a superb performer by increasing the COAL by 1.0mm are quite possibly barking up the wrong tree.

    Discussion? Any real-world data on how much the 6.5 Grendel can expect to gain loading 2.300 vs. 2.260?
    :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

    :: I Drank the Water :: Revelation 21:6 ::
  • cory
    Chieftain
    • Jun 2012
    • 2985

    #2
    When comparing two different COLs with the same charge I'd completely agree. However, you can only get so much powder into a COL of 2.26". Only increasing the COL to 2.3", I'd agree that the velocity gains may be marginal.

    Optimally I'd like a receiver and mags that'd allow me to load out to 2.36". I think they'd be a substantial amount of case capacity gained with the 127gr+ bullets.
    "Those who sacrifice liberty for security, deserve neither." Benjamin Franklin

    Comment

    • JASmith
      Chieftain
      • Sep 2014
      • 1620

      #3
      The added velcoity will still be less than one hopes for.

      Nonetheless, there are times when 50 fps makes a difference that means something in terms of maximum range for bullet expansion. Much less frequently are reductions in wind drift for competitive target shooters.

      To check this out, try running the 140gr Lapua Naturalis at 2200 and the. 2250 fps and check where the bullet drops below 2000 fps and the 10mph drift at 200 yards for the two muzzle velocities.

      Then, repeat for the 129 gr ABLR at 2300 and 2350 and see where this bullet drops below 1600 fps and the 10 mph drift at 500 yards for the two muzzle velocities.

      Last, decide for yourself how well you can dope wind. Most of us would think 2 mph is a calm wind, others moght be able to guess that a 10 to 15 mph wind is really about 10 mph, leaving 5moh uncertainty.

      The difference in drift resulting from the 50 fps is not likely to make much difference in one's ability to hit the vital zone at typical hunting ranges of under 300 yards, but might make a difference in score for the serious competitive target shooter at 600 yards.

      These observations are part pf the back story when you see folks advise going for an accuracy node near max (~100 fps?) instead of max velocity. The difference in accuracy from tuning the load may be greater than any gains realizable from the added powder.
      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

      • lrgrendel
        Warrior
        • Jul 2013
        • 662

        #4
        Great topic! Very interesting.

        This is pretty obvious to most, but those who are loading to a "COAL" or a magazine length and don't know where their "lands" are, and then read this. Just don't load out to 2.300" or longer without knowing where the rifling is. If you "jam" a bullet there could be an issue.

        Comment

        • rickOshay
          Warrior
          • Apr 2012
          • 784

          #5
          I did a calculation last year on this. The real world gains are very small, and perhaps indistinguishable for the average hunter.

          Just received an email from Satern saying they are now offering a Grendel II chamber.Can anyone elaborate on this? My understanding is the reamer takes out the compound throat. How many more different Grendel variants can we get!? Kind of getting annoying. This barrel will be used primarily for lighter bullets including Nos

          Comment

          • BluntForceTrauma
            Administrator
            • Feb 2011
            • 3897

            #6
            Excellent analysis, Greg, I had forgotten about that. And you even gave a full 0.100!

            Seems the only "free" velocity gains for a given cartridge are higher BCs or lighter bullets or — what I am questing for and people like GS Custom do a good job fulfilling — BOTH!

            The only other way to increase velocity is more pressure.
            :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

            :: I Drank the Water :: Revelation 21:6 ::

            Comment

            • cory
              Chieftain
              • Jun 2012
              • 2985

              #7
              I second the great analysis. I took the 1.4gr additional capacity and extrapolated my real world data out to an additional 1.4grs. Then for s**ts and giggles I stretched it out to 2grs.

              At 1.4gr I'm seeing an additional 100fps. That's 4" of free barrel length.

              From my real world date, my max loads were as follows.

              H.SST.140 - 31.4gr
              H.HPBT.140 - 30.8gr
              N.ABLR.129 - 30.2gr
              B.LRX.127 - 31.1gr



              It seems that extra 0.100" could make the 127gr LRX a feasible hunting option in the Grendel.
              "Those who sacrifice liberty for security, deserve neither." Benjamin Franklin

              Comment

              • FW Conch
                Warrior
                • Nov 2014
                • 289

                #8
                So ... where are you fellas getting the "free" powder?

                Just Askin ... :-)

                Comment

                • Variable
                  Chieftain
                  • Mar 2011
                  • 2403

                  #9
                  If I could pack in an additional 1.4 grains of powder without a ton of inconvenience--- I certainly would.
                  Life member NRA, SAF, GOA, WVSRPA (and VFW). Also member WVCDL. Join NOW!!!!!
                  We either hang together on this, or we'll certainly HANG separately.....

                  Comment

                  • Von Gruff
                    Chieftain
                    • Apr 2012
                    • 1078

                    #10
                    Whether there is any relevance or not my 6.5 Grendel Max that has the shoulder pushed forward by .050and the 123gn bullet seated out so there is a COAL of 2.405 has given a capacity increase that allows me to get the A Max to 2700fps with 32.6gn CFE 223 and exceptional accuracy for a light sporter 21inch barrel.
                    The 100gn ttsx ran at 2946fps over 34.1gn CFE 223

                    This has been a perfect upgrade for the Grendel in a micro action mini mauser in my estimation for my purposes.

                    Edit to add that I wasn't chasing max velocity but the accuracy node that best made use of all available capacity and components, it just happened to fall in the higher velocity zone
                    Last edited by Von Gruff; 06-28-2015, 01:02 AM.
                    http://www.vongruffknives.com/

                    sigpic Von Gruff



                    Grendel-Max

                    Exodus 20:1-17
                    Acts 4:10-12

                    Comment

                    • KentuckyBuddha
                      Warrior
                      • Oct 2012
                      • 972

                      #11
                      It is awfully nice that those solutions overlap though! I already kind of wish I had done my bolt action in Grendel Max.

                      Comment

                      • Von Gruff
                        Chieftain
                        • Apr 2012
                        • 1078

                        #12
                        Just for illustration

                        The 7.62x39, 6.5x39, Grendel, Grendel-Max(123gn A Max to 2.405) and the Grendel-Max with cast bullet

                        http://www.vongruffknives.com/

                        sigpic Von Gruff



                        Grendel-Max

                        Exodus 20:1-17
                        Acts 4:10-12

                        Comment

                        • BluntForceTrauma
                          Administrator
                          • Feb 2011
                          • 3897

                          #13
                          Excellent data, Gruff. I'd like to see a production "micro" bolt-action 65G that allowed for COAL of about 2.405.
                          :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

                          :: I Drank the Water :: Revelation 21:6 ::

                          Comment

                          • KentuckyBuddha
                            Warrior
                            • Oct 2012
                            • 972

                            #14
                            There is always fabricating. : )

                            Comment

                            • Variable
                              Chieftain
                              • Mar 2011
                              • 2403

                              #15
                              Originally posted by BluntForceTrauma View Post
                              Excellent data, Gruff. I'd like to see a production "micro" bolt-action 65G that allowed for COAL of about 2.405.
                              I don't know---- Then you'd have folks complaining about the massive jump to lands that factory Grendel fodder would have to make....
                              Life member NRA, SAF, GOA, WVSRPA (and VFW). Also member WVCDL. Join NOW!!!!!
                              We either hang together on this, or we'll certainly HANG separately.....

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