Observed ballistic coefficient of 123 AMAX

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  • Drifter
    Chieftain
    • Mar 2011
    • 1662

    #16
    Originally posted by bwaites View Post
    As for using .1 Mil for spindrift, well, I can't tell 1-1.5 inches at 600 yards is due to spindrift or my hold!
    Valid point. The slight breeze that I sometimes get at 600 is always left-to-right, and coupled with a small righthand spin drift, it can sometimes be enough to cause a miss on 10" steel at that distance. Adjusting 0.1-mil left is usually enough to keep me on the steel without having to guess the wind. I might be slightly left or right, but on target nonetheless. I hate missing...
    Drifter

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    • terrywick4

      #17
      Originally posted by bwaites View Post
      As for using .1 Mil for spindrift, well, I can't tell 1-1.5 inches at 600 yards is due to spindrift or my hold! I don't use any spindrift adjustment out to 1200 yards with my 7mm WSM, because I can't calculate that into my numbers, its simply to small a value in comparison to wind, barrel variation, my hold, etc.
      What kind of recipe do you use for your 7 WSM? I was/am using 120 grain A-Max and have had great success out to 575 yds. I am looking to go with maybe 139 grain or maybe little heavier.

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      • LR1955
        Super Moderator
        • Mar 2011
        • 3355

        #18
        Originally posted by BjornF16 View Post
        LOL…well, using "Ballistic" (JBM Ballistics iPhone app) for AA factory loaded Nosler 120 BT shot from my bolt Grendel at targets ranging from 375-700 yards resulted in a consistent .25 MOA delta between theory and actual…that was using the G1 BC on a "mild" boat tail bullet. Just lucky I guess.

        I will say that it wasn't nearly that close when I made a trip to Whittington and shot factory Hornady 123 A-Max on the high power silhouette range (200 - 500 meters) with my AR Grendel. I wasn't sure if it was due to zero'ing at 100 yards then swapping to meters (not likely) or optimistic G1 (on "moderate" boat tail bullet) across the Grendel velocities (more likely).

        I'll be upgrading my "Ballistic" program to the "AE" version in order to get Litz's G7 coefficients on my iPhone.
        Bjorn:

        You may notice differences past 600 because many programs use two algorithms. One to about 600 and another past 600.

        I use these things to get me close but don't expect them to be perfect. I also don't wonder why there may be differences between reality and these programs. I go with what I shoot.

        LR1955

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        • bwaites
          Moderator
          • Mar 2011
          • 4445

          #19
          Originally posted by terrywick4 View Post
          What kind of recipe do you use for your 7 WSM? I was/am using 120 grain A-Max and have had great success out to 575 yds. I am looking to go with maybe 139 grain or maybe little heavier.
          I shoot 168 Bergers over 62 gr of H4831 SC at about 3000 FPS or 180 Bergers over 64 gr of H1000 at 2950 FPS. Both are stunningly good to 700 and the 180s are slightly better at 1000.

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          • BjornF16
            Chieftain
            • Jun 2011
            • 1825

            #20
            Originally posted by LR1955 View Post
            Bjorn:

            You may notice differences past 600 because many programs use two algorithms. One to about 600 and another past 600.

            I use these things to get me close but don't expect them to be perfect. I also don't wonder why there may be differences between reality and these programs. I go with what I shoot.

            LR1955
            LIFE member: NRA, TSRA, SAF, GOA
            Defend the Constitution and our 2A Rights!

            Comment

            • calshipbuilder

              #21
              Originally posted by Drifter View Post
              Comprehensive list of Sources of Ballistic Program Inaccuracies on this link:



              The closing statement on the link is noteworthy:

              "When someone says that their un-tuned ballistic program was "right on at 1000 yards", I generally conclude that if they are telling the truth, they were lucky enough to have offsetting errors."
              Thanks for that link. I use the Shooter App. It has been great for my 300 win mag using Litz's G7 - got a second round hit at 1270 and only missed because I didn't call the wind right.

              Also, at 1065 yards it took 45.75 MOA of elevation to hit an IPSC target. Using a .247 G7 gave me 43.6 and a G1 of .475 said 44.0

              My guess is that as the 123 AMAX is into the transonic zone (~1200 FPS) at this distance, drag is increasing rapidly and killing my BC.


              1065 yards- Distance target was shot.
              2450 fps- Muzzle velocity
              45.75 MOA- Come up (elevation) increase from zero
              100 yards- Zero distance
              2200'- Elevation
              27.52- Pressure
              84.5 F- Temp
              31%- Humidity
              none- Wind speed and direction
              1:8.75"- Barrel twist

              2.5"- Sight Height (above bore)
              Last edited by Guest; 05-15-2013, 07:56 PM.

              Comment

              • bwaites
                Moderator
                • Mar 2011
                • 4445

                #22
                Originally posted by calshipbuilder View Post
                Thanks for that link. I use the Shooter App. It has been great for my 300 win mag using Litz's G7 - got a second round hit at 1270 and only missed because I didn't call the wind right.

                Also, at 1065 yards it took 45.75 MOA of elevation to hit an IPSC target. Using a .247 G7 gave me 43.6 and a G1 of .475 said 44.0

                My guess is that as the 123 AMAX is into the transonic zone (~1200 FPS) at this distance, drag is increasing rapidly and killing my BC.


                1065 yards- Distance target was shot.
                2450 fps- Muzzle velocity
                45.75 MOA- Come up (elevation) increase from zero
                100 yards- Zero distance
                2200'- Elevation
                27.52- Pressure
                84.5 F- Temp
                31%- Humidity
                none- Wind speed and direction
                1:8.75"- Barrel twist

                2.5"- Sight Height (above bore)
                That initial velocity is more than 200 FPS slower than what I used to determine that .247, so it may indeed be off a bit. Sierra quotes variable BC's based on velocity, some programs use a second calculation rate over 600 yards, so there is no true, exact BC that will work 100% of the time.

                They are estimates, use the figures you derive from experience. That's why it is so critical to keep a good record!

                Comment


                • #23
                  I found the G7 BC that the German guy uses for the 123gr A-MAX, and it is .218 out to 950m for him. He said that the 140gr A-MAX published BC works perfectly as-is, and I think this is out of a 6.5x284 bolt gun.

                  Comment

                  • Drifter
                    Chieftain
                    • Mar 2011
                    • 1662

                    #24
                    Originally posted by calshipbuilder View Post
                    Thanks for that link...

                    My guess is that as the 123 AMAX is into the transonic zone (~1200 FPS) at this distance, drag is increasing rapidly and killing my BC.
                    I was thinking that when posting. When I looked for some backup information online so that you wouldn't have to take my word for it, I ran across that list. Seemed appropriate to simply share all of it instead of just the small portion that was miraculously in my brain.

                    Originally posted by bwaites View Post
                    That initial velocity is more than 200 FPS slower than what I used to determine that .247...
                    At 2500 MV using the 123 A-max, your .247 G7 number agrees with my results out to 600. I notice that using your G7 BC in JBM shows ~0.5-mil more drop at 1k compared to running the numbers with the listed G1 BC.

                    Thanks for sharing your G7 estimation, as it may prove to be more accurate than the G1 at extended distances. I hope to see for myself eventually...
                    Drifter

                    Comment

                    • bwaites
                      Moderator
                      • Mar 2011
                      • 4445

                      #25
                      Originally posted by LRRPF52 View Post
                      I found the G7 BC that the German guy uses for the 123gr A-MAX, and it is .218 out to 950m for him. He said that the 140gr A-MAX published BC works perfectly as-is, and I think this is out of a 6.5x284 bolt gun.
                      Litz says the Berger 120 is .232 and the Sierra 123 is .260, and he measures them, doesn't estimate. .218 would suck! That would make the Amax quite a bit less aerodynamic than the Berger 120!

                      Comment

                      • calshipbuilder

                        #26
                        Here is a banded G1 that I am going to test out:

                        2450-1900 .51
                        1900-1275 .475
                        1275-1129 .45
                        1129-0 .4
                        Last edited by Guest; 05-16-2013, 07:45 AM.

                        Comment

                        • calshipbuilder

                          #27
                          Got some drops today, worked up a nice shooting load that matches the hornady AMAX load pretty well

                          123 Amax 2450 FPS, BLC(2), 18 inch barrel, lapua case

                          600 ft Elevation
                          29.26 inHg
                          78deg F
                          49.6% humidity
                          light crossing wind

                          100 yard zero

                          Yards - MOA
                          300 - 4.5
                          480 - 11
                          538 - 13.75
                          602 - 17.75
                          672 - 22
                          770 - 27.5
                          850 - 33.25
                          890 - 37

                          I confirmed each with at least 3 shots per distance.

                          I'm trying to fit a BC to it, but it drops off so fast at long range its hard to get something right. 233 G7 works OK, but my banded G1 doesn't

                          The 4.5 MOA 300 yard drop has also been confirmed on 2 different scopes (NF NSX and Sightron SIII)

                          Somebody tell me whats going on here
                          Last edited by Guest; 09-10-2013, 04:57 AM.

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                          • #28
                            I'm glad that I stumbled into this thread. I used the ballistics calculator on Hornady's website to figure out my come-ups. I plugged in all of the data (BC of .510 according to their website), then came to the G1/G7 selection. I wasn't sure of what this was so I looked it up. When I read that G7 was used for high BC bullets, I chose that one. The resulting ballistics chart looked fantastic (with a .510 G7)! I sure would have wasted a lot of ammo trying to figure out why my come-ups were so far off.

                            I just re-ran the data using a G7 of .247. The numbers look a lot more realistic now.

                            Comment


                            • #29
                              A .510 G7 would be insane. You would only need 3 scope hold-overs close to each other: Short, Medium, and Long. Getting into the .3's is high G7 BC territory, which the 140gr Secant bullets do in 6.5mm.

                              When I shot out to 1200yds with the 16" earlier this summer with the factory 123gr A-MAX, it was close enough to be just off the bottom edge of target.
                              Last edited by Guest; 09-10-2013, 07:16 PM.

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                              • calshipbuilder

                                #30
                                just ran my MV on a magento speed, averaged 2500 FPS, this confuses me even more

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