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.
Optimal Barrel Time (OBT) vs Optimal Charge Weight (OCW)
- Thread starter SplittingHairs
- Start date
When I first bought QuickLOAD I back tested loads I knew to be accurate, most from OCW or ladder tests.
Results were spot on.
Results were spot on.
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.
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.
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.
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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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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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.
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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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.
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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?
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.
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
Cheers,
Jim
Given the way this thread is drifting, I should add that QuickLOAD also lead me to different powders that gave me up to 100 fps additional,velocity with the same pressure or to a powder with very little,published data. Reloder 26 in my .300 Win Mag is a good example.
QuickLOAD is "only" a guide, but I'm finding it a very useful one.
Try it and see. You won't be disappointed.
Old thread, but here we go:
I have a OBT calculator I have written. Will take negative node values as well.
The data can be saved as a text file on your computer.
Link: OBT Calculator
I have a OBT calculator I have written. Will take negative node values as well.
The data can be saved as a text file on your computer.
Link: OBT Calculator
Interesting you brought back this OBT thread. I just did some obt testing with some interesting results. I have previously done testing with OBT with another cartridge but haven’t paid too much attention to it in this 6.5 prc I’m doing now.
So few months back, i put a 6.5 prc barrel in my savage action and just loaded up max loads for it. Did a pressure test to make sure it’s safe and just used that load. Shot many rounds through it in multiple sessions and they were all turds. 2.5 inch groups. After checking various torque settings and ensuring my loading steps were right, the groups just did not tighten up.
So this week I decided to calculate the obt node and go with that while simultaneously test many other reloading variables. Also got a A&D fix 300in to check weights of primers and powder. Thank the other thread with the tips on the scale on eBay!
Anyways. I just tested the loads today in windy rainy weather.
All of my groups shot way better groups compared to my previous load. Regardless of which variable in the load was changed, the group was better. The SD overall is better than the prior load but some variables were better than others, but also gets contradictory sometimes.
I guess what I’m trying to say is, I feel OBT works especially regarding group size.
My load is slightly out of alignment to the exact obt node but then none of this is exact given the ability to measure any of it. It’s all based on quick load predictions and estimated powder burn rates given the powder used is not in quick load.
Next is to test a load that’s slightly higher and slightly lower. The higher weight should get me closer to the calculated obt node and the lower weight should be the anti obt node.
If obt is really correct, I should expect the higher load to be even better than todays load, and the lower load to be worse.
So few months back, i put a 6.5 prc barrel in my savage action and just loaded up max loads for it. Did a pressure test to make sure it’s safe and just used that load. Shot many rounds through it in multiple sessions and they were all turds. 2.5 inch groups. After checking various torque settings and ensuring my loading steps were right, the groups just did not tighten up.
So this week I decided to calculate the obt node and go with that while simultaneously test many other reloading variables. Also got a A&D fix 300in to check weights of primers and powder. Thank the other thread with the tips on the scale on eBay!
Anyways. I just tested the loads today in windy rainy weather.
All of my groups shot way better groups compared to my previous load. Regardless of which variable in the load was changed, the group was better. The SD overall is better than the prior load but some variables were better than others, but also gets contradictory sometimes.
I guess what I’m trying to say is, I feel OBT works especially regarding group size.
My load is slightly out of alignment to the exact obt node but then none of this is exact given the ability to measure any of it. It’s all based on quick load predictions and estimated powder burn rates given the powder used is not in quick load.
Next is to test a load that’s slightly higher and slightly lower. The higher weight should get me closer to the calculated obt node and the lower weight should be the anti obt node.
If obt is really correct, I should expect the higher load to be even better than todays load, and the lower load to be worse.
