Question on ballistic app data inputs

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  • jackwagon
    Warrior
    • Jul 2017
    • 127

    Question on ballistic app data inputs

    Hey guys, I downloaded the Strelok app and was starting to input my data when I realized the 2580 fps for hornady black 123 gr is for a 24'' barrel, I am shooting an 18''.
    So the question is. Without a chrono is there a formula or base reduction for different barrel lengths?
    or anyone else with an 18'' that has used hornady black and has chrono data. I am just looking to get close.
    thanks.
  • VASCAR2
    Chieftain
    • Mar 2011
    • 6219

    #2
    When I've chronographed factory 123 grain A-Max it averaged 2464 FPS out of a Brownell's 18" Grendel II chamber (Satern/Liberty barrel) 1:8 twist on a 70 degree day. The Hornady 123 grain SST Factory averaged 2490 the same day with Magneto Speed Chronograph.

    Here is a picture of the velocity curve LRRPF52 has posted from the Grendel handbooks.
    Attached Files
    Last edited by VASCAR2; 09-14-2017, 01:29 AM.

    Comment

    • jackwagon
      Warrior
      • Jul 2017
      • 127

      #3
      Vascar2, the hornady SST are also listed at 2580 and you chrono-ed at 2490. So you lost around 15 fps per inch. The graph you listed looks like its around 10fps ? maybe. This should give me a starting point that's closer, thanks for the help.

      Comment

      • Sticks
        Chieftain
        • Dec 2016
        • 1922

        #4
        I am shooting a 18" Barlitien, which is stabilized at 2475 for ELD, Amax, and SST (123gr).
        Sticks

        Catchy sig line here.

        Comment

        • jackwagon
          Warrior
          • Jul 2017
          • 127

          #5
          Originally posted by Sticks View Post
          I am shooting a 18" Barlitien, which is stabilized at 2475 for ELD, Amax, and SST (123gr).
          Thanks Sticks. Is your barrel a 1:8 twist also?

          Comment

          • grayfox
            Chieftain
            • Jan 2017
            • 4295

            #6
            To get real good data... might as well admit it... try to get a chrono. I know there are several but I use a magnetospeed and it's been super.
            And range-friendly and sun/clouds-INsensitive.
            Barrels can and do differ, I have 1 18"-er that's fast (the Amax and SST's run 2510 in mine) but the Hdy Black runs slower, I don't know why but that's what it is.
            So the chrono is really worth it to you. Especially if you want to reload.
            Just a thought.
            "Down the floor, out the door, Go Brandon Go!!!!!"

            Comment

            • VASCAR2
              Chieftain
              • Mar 2011
              • 6219

              #7
              What part of Indiana are you in Jackwagon? I live close to Vincennes Indiana only on the other side of the river. I have a PACT chronograph and a Friend has a Magnetospeed chronograph.

              Comment

              • Sticks
                Chieftain
                • Dec 2016
                • 1922

                #8
                Originally posted by jackwagon View Post
                Thanks Sticks. Is your barrel a 1:8 twist also?
                Yes it is

                Originally posted by grayfox View Post
                Barrels can and do differ, I have 1 18"-er that's fast (the Amax and SST's run 2510 in mine) but the Hdy Black runs slower, I don't know why but that's what it is.
                So the chrono is really worth it to you. Especially if you want to reload.
                Just a thought.
                Best advice here. A simple Chrono will run you $99 or so, then you will have accurate info on what your rifle does with each ammo. Extrapolating data from other users with the same barrel length, twist, and hopefully the same mfg as yours will get you close, then you can dial it in shooting long range (500y or more).
                Sticks

                Catchy sig line here.

                Comment

                • jackwagon
                  Warrior
                  • Jul 2017
                  • 127

                  #9
                  Originally posted by grayfox View Post
                  To get real good data... might as well admit it... try to get a chrono. I know there are several but I use a magnetospeed and it's been super.
                  And range-friendly and sun/clouds-INsensitive.
                  Barrels can and do differ, I have 1 18"-er that's fast (the Amax and SST's run 2510 in mine) but the Hdy Black runs slower, I don't know why but that's what it is.
                  So the chrono is really worth it to you. Especially if you want to reload.
                  Just a thought.
                  Thanks guys. A chronograph is on my list, but as i'm heading to the 750 yd range this weekend I thought I would try to get the data a little closer .

                  Comment

                  • jackwagon
                    Warrior
                    • Jul 2017
                    • 127

                    #10
                    Originally posted by VASCAR2 View Post
                    What part of Indiana are you in Jackwagon? I live close to Vincennes Indiana only on the other side of the river. I have a PACT chronograph and a Friend has a Magnetospeed chronograph.
                    I am in the South Bend area, up by the Mi state line.

                    Comment

                    • jackwagon
                      Warrior
                      • Jul 2017
                      • 127

                      #11
                      Originally posted by Sticks View Post
                      Yes it is



                      Best advice here. A simple Chrono will run you $99 or so, then you will have accurate info on what your rifle does with each ammo. Extrapolating data from other users with the same barrel length, twist, and hopefully the same mfg as yours will get you close, then you can dial it in shooting long range (500y or more).
                      That was the plan.... As I need all the help I can get.

                      Comment

                      • grayfox
                        Chieftain
                        • Jan 2017
                        • 4295

                        #12
                        Also... get the Grendel handbooks vol 1 and vol 2.

                        We just started a new print run of Volume I (4th Printing) and Volume II (2nd Printing). No changes were made to Volume I from the 3rd Printing, which includes the updated Western Powders data from 2014. Some slight changes were made to Volume II. We fixed a small typo on page 48 referring to figure 6.7 when it should


                        Best Grendel book $$ you can spend.

                        I grew up in Marion, went to Scout camp just east of Warsaw.
                        "Down the floor, out the door, Go Brandon Go!!!!!"

                        Comment

                        • J.Boyette
                          Unwashed
                          • Nov 2017
                          • 8

                          #13
                          @jackwaggon,

                          Typically 50fps per inch is the normal measurement for going up or down for barrel est...

                          Comment

                          • Klem
                            Chieftain
                            • Aug 2013
                            • 3507

                            #14
                            What you could do that is more precise is shoot groups at your 750yd range and note the drop.

                            Zero for 100 and then record the drop for each 100 beyond that. Or, if ammo and time is a factor shoot a few groups at 300 and 700yds. Then play around with Strelok to predict the velocity by matching the actual drops to a particular velocity. Normally we determine velocity first and use that to predict drop at various distances. This way you are doing it the reverse.

                            Kestrel's with Applied Ballistics have a feature where you enter the chronographed velocity, shoot at a known distance and notice the difference between the predicted drop and actual drop. Then return to the kestrel and enter this difference to fine-tine your velocity. This is because all chronographs come with a margin of error. The Chony I use states it can be up to 5% error. Add to that any further error from the way it is set up on the day and it's unlikely the chronograph is going to exact. 5% of 2,500fps is 125fps which is a fair error and might explain why your bullets don't land exactly where your ballistics program says they should land. I don't know if Strelok has a similar feature to Applied Ballistics and maybe someone else can chime in here.

                            But...the other guys are right, you will need a chronograph at some stage if you ever want to do meaningful load development.

                            Comment

                            • LR1955
                              Super Moderator
                              • Mar 2011
                              • 3355

                              #15
                              Originally posted by J.Boyette View Post
                              @jackwaggon,

                              Typically 50fps per inch is the normal measurement for going up or down for barrel est...
                              Boyette:

                              I think you are confusing elevation changes with barrel length.

                              I believe that barrel length is something like 25 or 30 fps per inch and isn't linear.

                              It is generally considered that a 50 - 60 fps difference in velocity equate to one minute of elevation.

                              LR55

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