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Optimal Barrel Time (OBT) vs Optimal Charge Weight (OCW)

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  • Optimal Barrel Time (OBT) vs Optimal Charge Weight (OCW)

    I was wondering if anyone has used Quickload OBT and compared this with OCW to see how if they result in similar load data. I have shot my most accurate / smallest groups using OBT.

  • #2
    When I first bought QuickLOAD I back tested loads I knew to be accurate, most from OCW or ladder tests.

    Results were spot on.

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    • #3
      I've found OBT to correspond to good nodes, after truing data in Quickload. The flip side is that OBT doesn't capture all possible nodes. There's a huge gap between the high node and the low node, and with some bullet/cartridge combos you can't hit the high node without pressure. There are good nodes between that often will work well.

      These days I use chrono data looking for velocity flat spot in conjunction with OCW approach looking for consistent POI on target. Find a good node that encompasses both of those, tweak seating depth if needed to tighten up groups further. That's been very effective for me.

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      • #4
        What Sheldon said, OBT captures the largest nodes and if you have good input data you tend to get great results out of it. I did OCW after the fact and found other use able nodes but they were not as big nor quite as good as those found with OBT.

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        • #5
          I appreciate each of your responses. I have a excel file with each load I have reloaded and chronograph data for the days I took that equipment to the range. I reload for 25-06, 308 Win, 5.56 Nato, 300 Blackout, 6.5 Creedmoor, 458 SoCom, 12 GA shotgun and 9mm, 45 ACP, 40 S&W, 357 Magnum. It has developed into quite a hobbie!

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          • #6
            Here is a sample of the data I have collected

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            • #7
              How many decimal places on the OBT is important. Chart goes to four and the obt calculator goes to three. Seems like two should be adequate because it sort of starts to fall apart at the lower and higher ambient temperature range when compared to the temperature on the day you gathered your data and called it.
              “The problem with quotes on the Internet is you never know if they are genuine.”
              ― Joseph Stalin

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              • #8
                Originally posted by Culpeper View Post
                How many decimal places on the OBT is important. Chart goes to four and the obt calculator goes to three. Seems like two should be adequate because it sort of starts to fall apart at the lower and higher ambient temperature range when compared to the temperature on the day you gathered your data and called it.
                Think in terms of significant figures. It's not trivial getting better than 2 sig figs in many real world measurements. Getting to 4 typically means there is quite a bit of control in the system. In terms of a calculator, there's no harm in using one or two more digits than the data variability supports as long as you understand the last one or two may be insignificant.

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                • #9
                  We'll, .001 is one millisecond. In QL they show it as 1.000 m/s. So, that third spot is thousands of a m/s. A fourth place would be ten-thousands of a m/s. What is the confidence level of the OBT calculation, 90%? If so, they overlap. There needs to be some sort of +/- of it. Even the creator says it is a calculated estimate but doesn't give an estimated error rate.
                  “The problem with quotes on the Internet is you never know if they are genuine.”
                  ― Joseph Stalin

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                  • #10
                    I forgot to state that both the 308 & 6.5 CM data is being shot from 24" long barrels. As shown on the sample data, not all of the OBT are aligned to the natural barrel frequencies. I started searching for accurate loads by reading and then loading load ladders. I found this to use up a great deal of components, without much success. So I read some more, learned about the OCW approach and the OBT approach. I decided to buy a copy of Quickload and pursue the OBT approach. I have yet to investigate seating depth variations, while using OBT loads, to see if that kind of minor adjustment can improve a group size for me. I will admit that I still have much to learn, but I am enjoying the journey.

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                    • #11
                      Unfortunately, OBT is in hypothesis stage no different than OCW and other similar methods. All have unexplained variables that prevent proving why they do or don't work. When it does work the coincidence bug-a-boo is ignored. Not exactly the scientific method. When it doesn't work the person believes he did nothing wrong. Like a Stradivarius will sound the same as a high school violin given the same set of strings and bow.
                      Last edited by Culpeper; 09-19-2017, 06:36 AM.
                      “The problem with quotes on the Internet is you never know if they are genuine.”
                      ― Joseph Stalin

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                      • #12
                        Originally posted by Culpeper View Post
                        Unfortunately, OBT is in hypothesis stage no different than OCW and other similar methods. All have unexplained variables that prevent proving why they do or don't work.
                        And what are those?

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                        • #13
                          Please don't quote me out of context. I did give that explanation with sufficient detail. But for those that can't see the elephant in the room, Bad shooting, good shooting, lousy rifle, good rifle, a good day, a bad day, good reloading, bad reloading. And so on and so forth. When it does work it is usually reported just for that day or one particular group and calling it never to be posted again. Next time out something other variable is screwing up the groups. They are not theories that have been proven and probably never will be. They are just hypothesis with plenty of of shooters reporting success or failure with nothing to explain why or why not. It just does or does not is all that is explained. What would be interesting is getting three identical rifles and posting results. Then get three different rifles and posting results. A node is a node is a node. Right?
                          “The problem with quotes on the Internet is you never know if they are genuine.”
                          ― Joseph Stalin

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                          • #14
                            Originally posted by Culpeper View Post
                            What is the confidence level of the OBT calculation, 90%? If so, they overlap. There needs to be some sort of +/- of it. Even the creator says it is a calculated estimate but doesn't give an estimated error rate.
                            I'm not surprised there is no error estimate given. If you've read the Litz books, you can get a feel for how hard it is to link mathematical models to real shooting results, especially at long range. For shorter range like if you are doing OCW or OBT at 100 yards, an excellent shooter would have a decent chance at modeling uncertainty. For many people, operator error is a very significant part of the equation.

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                            • #15
                              Yes, I've read a couple of them.
                              “The problem with quotes on the Internet is you never know if they are genuine.”
                              ― Joseph Stalin

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                              • #16
                                I look at both methods as good tools. I like to start out with OBT using Quickload to get close then I will do an OCW to dial it in tighter and in the end OAL to get the most out of the load as I can. This has worked well for me but there are lots of methods that work well for others.

                                Cheers,

                                Jim

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