Quickload for optimum load selection, or not.

[big5ifty]

It's been mentioned a couple of times to me, that QL is an economical way to find optimum loads, or loads that are POI stable in spite of moderate temperature changes.

I've done some reading on the subject, and from the information available by people who have done this, the subject of Optimum Barrel Time is involved.

To begin formulating an indicative prediction from QL, you have to measure your case capacity. This is typically done with water.

Then, you have to true the powder burn.

Then, you have to test a small range of charges around the QL prediction, to verify it is actual.

The concept of optimum barrel time is complicated.

OBT Explained

This statement by the author is important :

"I was able to arrive at the optimum charge weight almost without any workup, as I could start just below the weight predicted, and observe the groups as the charge was slowly increased. "

And leaves me to conclude that the mathematics involved in OBT are to explain why the OCW method works.

I'm not sold on load development with the Quickload OBT idea. There are many critical variables, and with anything complicated, something easily goes wrong.

Firstly, measuring case capacity is difficult and time consuming. Try it yourself, measure the same case capacity 5 times.

Secondly, you have to shoot some rounds to determine maximum safe pressure.

Third, you have to shoot groups around the QL prediction, to verify it is true.

Getting close to a predicted node and testing charges around it is in fact what OCW is for.

I can find an OCW node in 16 rounds. 4 rounds per charge, 4 charges, spaced 0.5% apart. I don't have to care about measuring case capacity, and I don't have to fire test rounds to true the powder burn for QL.

I will then use 12 more rounds to confirm the node by loading 4 rounds each at the mode, and 0.25% above and below.

It could be argued that the number of shots can be reduced to 3, I prefer to use 4, in case something goes wrong with 1 shot, then three remain to paint the picture.

Can a QL predicted accuracy node be developed and proven on target in 28 rounds ?

If you use QL that way, please share the details of your process, with attention to the total number of rounds required to reach a conclusion.

[Tripodmvr]

Have a look at the attached calibrated calculation. I pre-calculated charges using the default value of 0.500 for the Burning Rate Factor. We loaded 3 cartridges with 69, 70 and 71gr of S355. These were shot over the chrony and I then did the calibration (changing only the BRF to get the speed recorded), loaded ten more at 71gr and shot 5 more shots. This gave a MOA group at 100m. My friend then hunted with these loads and was very successful. Total of 8 shots to get going.

Measuring the water weight of a case is easy. Weigh empty case and then fill to level with the case mouth. Soapy water helps to break surface tension to get a level water line. Weigh again and get the H2O volume needed. Repeat with two to four others to get a mean.

I have done about 1500 calculations that have achieved a 95% success rate. Accurate and consistent measured speed is essential as well as low ES.

[big5ifty]

You've matched your QL output to your node 5.

That seems simple enough, thanks for the explanation.

How will that barrel time change with say a 10 degrees Celcius increase and decrease in powder temperature ?

[Tripodmvr]

A node has a certain bandwidth that can be about 1 grain wide. If you then load to the upper part in summer, then the lower temps and burning rate in winter might still keep you within that accuracy band. The charge then would not need to be adjusted. With target shooting you can always shoot from a cool bag where you can keep an even temperature.

[big5ifty]

Having found the correlation between a possible actual result and the predicted GRT OBT in 12.7x99, I re-looked at my load data for .375 RUM.

GRT predicts my velocity to within 20 fps of actual, with no parameter changes.

I had what I belived to be an OCW node at 93.5 grains N555, and according to the software, my barrel time is 0.09 ms slower than the predicted OBT.

To my mind then, it indicates that calculated OBT is a reasonable mathematical equivalent of the OCW method.

I like to be sure about things, which is why I like to see the group dispersion and center changes on paper as well, so I can't see myself replacing my OCW tests with just what GRT tells me.

Using both is proving very useful, because with the 12.7x99, I could see I was near a node both at 243.5 grains 24N41 and 236.5 on paper, I just wasn't sure if I was before or after the node at that charge.

GRT indicates that it's just shy of the node, and because I don't want to go higher with the charge, I will re-test on the lower node.

[Againstthegrains]

I have used Gordon's Reloading Tool, and have come unstuck quite a few times, as the powder burn rates are not quite right for the prediction, or the batches of powder vary wildly. Whichever it is. The bottom line, is that to measure is to know, so the OBT nodes correspond very well with the barrel length and measured velocity combos.

To use the OBT method, I use the program to tell me what speed I need for my barrel length to reach a particular node. I then use their powder charge weight as a guide, and test powder charges above and below the predicted, until I reach the velocity I want, which is invariable on the node.

You must do this with a chrony, otherwise, you are working in the dark.

[Tripodmvr]

I have used Gordon's Reloading Tool, and have come unstuck quite a few times, as the powder burn rates are not quite right for the prediction, or the batches of powder vary wildly. Whichever it is. The bottom line, is that to measure is to know, so the OBT nodes correspond very well with the barrel length and measured velocity combos.

To use the OBT method, I use the program to tell me what speed I need for my barrel length to reach a particular node. I then use their powder charge weight as a guide, and test powder charges above and below the predicted, until I reach the velocity I want, which is invariable on the node.

You must do this with a chrony, otherwise, you are working in the dark.

Did you not use the OBT feature where you can give the actual speed and it calibrates the burn rate and adjusts that to fit the figures. Now you can calculate the charge to achieve the node. In Quick Load I have to do that manually.

[Treeman]

Did you not use the OBT feature where you can give the actual speed and it calibrates the burn rate and adjusts that to fit the figures. Now you can calculate the charge to achieve the node. In Quick Load I have to do that manually.
[/quote]
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Please give more about this OBT feature ?

[Tripodmvr]

I am not a GRT fundi so bear with me. This is a screen print of GRT with details of a load with my Ruger 243. The speed should read as 2837fps. I will now try and show how to get there.

[Tripodmvr]

This is a new window that opens when the clock, with OBT in the middle, at the top is clicked.

[Tripodmvr]

I changed the speed to 2837 and then clicked the compute OBT button.

[Tripodmvr]

The actual barrel time (BLT) is shown and the OBT time as well. If I now click compute node charge adjustment then the charge is displayed as well as the calculated speed at the top. To amend the initial calc and save the calibration click on Create grtload file.

Hopefully I have the sequence correct for you to follow. With Quick Load I calculated 41,55gr and node speed of 2924fps. Pressure of 53K psi.   

[janfred]

How does the GRT caculation agree with your QL results?

[Tripodmvr]

I have confused myself with the figures presented as I used 2 different lots of S365 with a big variation in burning rate. The principles shown however depict the correct method.

Node 5
GRT   40,3gr = 2850fps
QL    41,55gr = 2927fps

[Treeman]

Now that is bedondered interesting !
Like seriously "wow!"