Question on ballistic app data inputs

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  • LRRPF52
    Super Moderator
    • Sep 2014
    • 8569

    #16
    Originally posted by VASCAR2 View Post
    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.
    That's right where most 18" have chrono'd for me as well with that load and conditions.

    Usually in the high 2400s-low 2500s with a factory Hornady 123gr, and low 2500s with an AA 123gr Scenar load.

    There are a bunch of threads with scores of chrono samples already that I've posted across many different 18" barrels that I personally did, along with posts from others with their 18" data as well.
    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

    • jackwagon
      Warrior
      • Jul 2017
      • 127

      #17
      Originally posted by Klem View Post
      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.
      So just to update since this original post was awhile ago. I ended up using 20 fps/per inch, sat down at the 500 yard bench, dialed in the mils listed on the Strelok app and took 3 shots that went to the dead center of ??? Since I couldn't see where they went with my 10x42 I dialed back to my zero. I had a holdover card from last range trip that was out to 350yds so using that and 3 more rounds I found 500. I wasn't able to get to the 750 yd bench as SAMMY SNIPER AND HIS SEAL TEAM must have made reservations for the whole day. Due to the 3 hour drive each way and trying to test 2 many things( by myself) at each range trip it is certainly a challenge, but im enjoying it. Thanks to all on here for your help.

      Comment

      • Klem
        Chieftain
        • Aug 2013
        • 3507

        #18
        '3-hr drive each way', that's dedication.

        What did you have to dial to get on 500? And where did it land relative to the Point of Aim?

        Comment

        • jackwagon
          Warrior
          • Jul 2017
          • 127

          #19
          Originally posted by Klem View Post
          '3-hr drive each way', that's dedication.

          What did you have to dial to get on 500? And where did it land relative to the Point of Aim?
          Klem, the Strelok app says 3.92 MRAD /70.55''/ 39.2 clicks I dialed this in initially but never saw any signs of impact, instead of wasting ammo I went back to zero on the scope and held at the 4 mil mark ( SWFA 10X42) so none of my hits were dialed. When I held at the very tip of the triangle at 4 mil mark I was hitting every time. Precision...probably not, acceptable to me...yep

          Comment

          • LR1955
            Super Moderator
            • Mar 2011
            • 3355

            #20
            Originally posted by jackwagon View Post
            Klem, the Strelok app says 3.92 MRAD /70.55''/ 39.2 clicks I dialed this in initially but never saw any signs of impact, instead of wasting ammo I went back to zero on the scope and held at the 4 mil mark ( SWFA 10X42) so none of my hits were dialed. When I held at the very tip of the triangle at 4 mil mark I was hitting every time. Precision...probably not, acceptable to me...yep
            JW:

            So you went back to your 100 yard zero? If so, 4 mils come up should be a hit at 500.

            It isn't magic. Most every modern target cartridge today needs 12 - 14 minutes of elevation between 100 and 500. The differences between cartridges exists but is measured in the 1 minute or so range when shooting at 500 yards. Past 500 yards is where a person sees enough difference that they need to be pretty precise in their elevation. However, if they get a solid zero at 500 yards my bet is that if they indexed another 14 minutes on the elevation that they would get hits at 750 yards on a two minute target.

            Anyway, once you get some chrono data and input it into your app, and then shoot and compare things, I bet you will be around 14 minutes of elevation between 500 and 750 with your Grendel cartridge and that you will get hits on a two minute 750 yard distant target.

            LR55

            Comment

            • Klem
              Chieftain
              • Aug 2013
              • 3507

              #21
              Originally posted by jackwagon View Post
              Klem, the Strelok app says 3.92 MRAD /70.55''/ 39.2 clicks I dialed this in initially but never saw any signs of impact, instead of wasting ammo I went back to zero on the scope and held at the 4 mil mark ( SWFA 10X42) so none of my hits were dialed. When I held at the very tip of the triangle at 4 mil mark I was hitting every time. Precision...probably not, acceptable to me...yep

              Jack, is your SWFA a Mils/Mils scope or a Mils/MOA? if you are using a SWFA 10*42 which has a Mildot reticle and 1/4MOA clicks on the turrets that might explain why you can hit with the reticle but not when using the turrets.

              I understand you dialled-up but missed the target at 500. Then dialled back to zero and used the Mils reticle to hit the target. Strelok's Mils and inches are correct but the 39.2 clicks are configured for a 0.1Mil scope. Your Strelok is configured for a Mils/Mils scope and you might have a Mils/MOA model.
              Last edited by Klem; 11-13-2017, 04:17 AM.

              Comment

              • bj139
                Chieftain
                • Mar 2017
                • 1968

                #22
                Klem,
                SWFA scopes are available in MIL/MIL. I have two as well as one MIL/MOA.
                Maybe you already know Jack has a MIL/MOA. I couldn't find anything in his post to indicate he does.

                Comment

                • Klem
                  Chieftain
                  • Aug 2013
                  • 3507

                  #23
                  Originally posted by bj139 View Post
                  Klem,
                  SWFA scopes are available in MIL/MIL. I have two as well as one MIL/MOA.
                  Maybe you already know Jack has a MIL/MOA. I couldn't find anything in his post to indicate he does.
                  I don't know for certain what model he has. No doubt he will chime in when he reads this. A Mils/MOA scope would explain why he hit the target using the reticle but could not if he dialled up the 39.2clicks on an 1/4MOA MOA turret.

                  Comment

                  • JASmith
                    Chieftain
                    • Sep 2014
                    • 1620

                    #24
                    Harking back to the OP -- there are calculators to estimate change in barrel length. I created the referenced chart using the velocity estimator app I wrote a few years ago.

                    You can get to it through the Grendel load data in ammoguide.com using reference load data already existing in the data base. The over 600 loads for the Grendel there cover almost all reasonable powder and bullet combinations. (yes there are a few not there!!!)

                    Alternatively, you can enter your own reference load here: Velocity Estimator
                    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

                    • jackwagon
                      Warrior
                      • Jul 2017
                      • 127

                      #25
                      Originally posted by Klem View Post
                      Jack, is your SWFA a Mils/Mils scope or a Mils/MOA? if you are using a SWFA 10*42 which has a Mildot reticle and 1/4MOA clicks on the turrets that might explain why you can hit with the reticle but not when using the turrets.

                      I understand you dialled-up but missed the target at 500. Then dialled back to zero and used the Mils reticle to hit the target. Strelok's Mils and inches are correct but the 39.2 clicks are configured for a 0.1Mil scope. Your Strelok is configured for a Mils/Mils scope and you might have a Mils/MOA model.
                      So I do have the mil/mil scope, and I used 2475fps. I think that I may have found part of the problem
                      as I went back over the strelok data I have 2.25'' scope height on my phone, and 2.5'' input on my tablet which I took to the range last time, I don't remember off the top of my head which is right( possibly neither since I think I got the info from u tube) will have to research this more.

                      So I think when I dialed the scope it was possibly just high - probably why I didn't see anything. I did consider dialing the scope again but with no zero stop/no spotter I was afraid of getting lost...

                      Comment

                      • terrywick4
                        Warrior
                        • Sep 2014
                        • 181

                        #26
                        +1 to LR1955. I use 22 fps per inch and usually it is close to the labradar.

                        Originally posted by LR1955 View Post
                        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

                        Comment

                        • Klem
                          Chieftain
                          • Aug 2013
                          • 3507

                          #27
                          A difference of .25" for sight height is not going to make much difference. If you enter both heights into your program; 2.25" and 2.5' and keep everything else the same, the difference in drop is only 1" at 500yards. I use 2.5" as a default for AR's.

                          If you hit the target using a 4mil hold-over on the reticle but missed when you dialled the same on the turrets then maybe the wind got you, or dare I say it, a more ordinary reason.

                          How big is your target?
                          Last edited by Klem; 11-13-2017, 10:39 PM.

                          Comment

                          • jackwagon
                            Warrior
                            • Jul 2017
                            • 127

                            #28
                            Originally posted by Klem View Post
                            A difference of .25" for sight height is not going to make much difference. If you enter both heights into your program; 2.25" and 2.5' and keep everything else the same, the difference in drop is only 1" at 500yards. I use 2.5" as a default for AR's.

                            If you hit the target using a 4mil hold-over on the reticle but missed when you dialled the same on the turrets then maybe the wind got you, or dare I say it, a more ordinary reason.

                            How big is your target?
                            You can say it... I certainly thought it. The target was 8''

                            Comment

                            • Klem
                              Chieftain
                              • Aug 2013
                              • 3507

                              #29
                              Originally posted by jackwagon View Post
                              You can say it... I certainly thought it. The target was 8''
                              There's your answer. An 8" target at 500yards is way too small for load development. Great for target practise when you square away your sights and ammo but right now you need a target that is as big as possible to see what's going on.

                              Especially when starting out with new loads and gun. The gun may only be capable of 2MOA which means the average group size at 500yards will be 10". Some bullets will always miss the target and there's not a damn thing you can do about it. Plus you don't yet know the velocity of your bullets.

                              I would suggest a minimum of 3ft square at that range. You can always 'borrow' a Corflute plastic sign on the side of a road if looking for something that big. Retailers sometimes leave them out at night...

                              Comment

                              • bj139
                                Chieftain
                                • Mar 2017
                                • 1968

                                #30
                                Originally posted by Klem View Post
                                There's your answer. An 8" target at 500yards is way too small for load development. Great for target practise when you square away your sights and ammo but right now you need a target that is as big as possible to see what's going on.

                                Especially when starting out with new loads and gun. The gun may only be capable of 2MOA which means the average group size at 500yards will be 10". Some bullets will always miss the target and there's not a damn thing you can do about it. Plus you don't yet know the velocity of your bullets.

                                I would suggest a minimum of 3ft square at that range. You can always 'borrow' a Corflute plastic sign on the side of a road if looking for something that big. Retailers sometimes leave them out at night...
                                There are a few election signs around here that need removing.

                                Comment

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