OCW method - second rifle test

I think you know that I have been into Quick Load for a long while. It would be interesting to evaluate your results using QL to see if there is a correlation between the two methods. Did you record speed whilst shooting? If so, I can do calculations to try and assist with load development.

The speeds I recorded on the day looked odd, it's possible that between the identical numbers the reading wasn't picked up due to muzzle blast.

These numbers were round robin, so in order of the columns, not rows : 2337, 2337, 2777, 2777, then column two, etc.

101 - 2737, 2789, 2766
102 - 2737, 2777, 2789
103 - 2777, 2777, 2770
104 - 2777, 2803, 2842

I'm really not concerned with the velocity yet, I did tests previously measuring virgin brass after firing with a 1/10,000 micrometer, and the N570 gave highest velocity for the least case head expansion, and 104 grains is the most expansion I want to have on the brass.

What distance was the chrony at?

and 104 grains is the most expansion I want to have on the brass.

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could you please tell us more about this ?
Perhaps even start a thread detailing this matter of expansion, what, why and how.

and 104 grains is the most expansion I want to have on the brass.

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could you please tell us more about this ?
Perhaps even start a thread detailing this matter of expansion, what, why and how.

You can refer here :

Measuring for pressure .

What distance was the chrony at?

5 meters. Most likely too close.

5 meters. Most likely too close.

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There I was thinking I was overdoing it a tad, 5 m + then ???? :o :o

With an optical chronograph the escaping gases can trigger the light sensors and give a false reading. My suggestion has always been 5m especially when the big powder burners are used. The RUM, burning 104gr of propellant has a massive gas emission and it might be a good idea to place the chrony at say 10m. Actual speed at the muzzle is easy to calculate.

What barrel length does the 375RUM have?

What barrel length does the 375RUM have?

30"

What barrel length does the 375RUM have?

30"

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My word :o I never knew there were rifles with barrels that long, I wonder if I have ever even seen one that long?

I've had good results with this OCW method across 3 different caliber target rifles.

This is for my 308 Norma, my 168 Bergers are finished, now I'm going to use 155 Nosler CC, and change powder from IMR to Vihtavuori. This result clearly illustrates what the OCW test is about.

I went according to the load data for the cartridge, the max load is 0.2 grains over book, and the charge increments are 0.3 grains, or 0.5% of charge weight.

What is very interesting is that the first group is the largest, in OCW it's called the scatter node, and the fifth group is exactly 1.5% higher powder charge from that.

I've seen the same principles manifest on paper in each of the tests I've done, it just happens that this particular test records clearly and obviously from the scatter node to the OCW node on the same paper.

The top left shot in group 4 I'm treating as pulled, as well as the bottom right in 6. That leaves 14 shots across a charge difference of 0.6 grains, or 1%, all grouping around the same point.

Thanks for the write-up very interesting! Do you shoot 1 shot per charge weight, repeated 4 times?

Do you use QL and if so how does this correlate to QL?

That's a very nice target to use for the exercise - where is it from as never seen them?

Round robin, 1 shot per charge, 4 shots per string, 5 minutes to cool down, repeat.

This is not using QL or GRT, just the load data in the book for the max load, and charge weight jumps that covers about 2% of the charge weight.

The target is what they sell at the Guns@Work range.

I do use GRT to compare case fill and burn rate of various powders, but I do not rely on the software to find a load, just what's on the target.

These are very good value for money and work well for this kind of test.

3" splatter target

Th

Round robin, 1 shot per charge, 4 shots per string, 5 minutes to cool down, repeat.

This is not using QL or GRT, just the load data in the book for the max load, and charge weight jumps that covers about 2% of the charge weight.

The target is what they sell at the Guns@Work range.

I do use GRT to compare case fill and burn rate of various powders, but I do not rely on the software to find a load, just what's on the target.

Thank you for the info. Why are you not using GRT to find a load?

My offer of 6 June is still open

I think you know that I have been into Quick Load for a long while. It would be interesting to evaluate your results using QL to see if there is a correlation between the two methods. Did you record speed whilst shooting? If so, I can do calculations to try and assist with load development.

Thank you for the info. Why are you not using GRT to find a load?

I would not do that, because I am a programmer by trade, and I know that no code ever written can predict the real world, it can only approximate.

GRT is not always correct.

For example, the load I worked up with N570 in my 375 RUM comes up over 100 fps short in GRT.

I know I can go and tweak the burn rate to improve the software model, but I prefer not to go test loads to collect data just to do that, as it is not necessary.

The way I end up choosing a load is simple, and gives results within 30 rounds.

I would not do that, because I am a programmer by trade, and I know that no code ever written can predict the real world, it can only approximate.

GRT is not always correct.

For example, the load I worked up with N570 in my 375 RUM comes up over 100 fps short in GRT.

I know I can go and tweak the burn rate to improve the software model, but I prefer not to go test loads to collect data just to do that, as it is not necessary.

The way I end up choosing a load is simple, and gives results within 30 rounds.

I have done close to 1500 calculations with QL, of which about 95% gave accuracy at the predicted speed. The best I have achieved so far was to calculate and get confirmation for a load with a 375HH. It only took 8 shots to get the hunting load and that included a grouping of 3 shots. With the cost of your calibre's components, that will be a big saving. Nodes are normally a band and QL gets you close. Actual shooting with increments of say 0,3gr will establish the band width and show the best accurate load.

I should have qualified my statements above.

1. Predictions for loads using defaults on QL are not accurate and might be useful to check supplied factory loads.
2. My calculations are done using the following data :
a) Measured barrel length
b) Measured water case capacity of a fired case
c) COL of cartridge from base to tip of bullet (used to calculate case fill)
d) Charge used and speed achieved

Those figures are then entered into QL and a charge calculated to get the barrel time correct for the specific length of barrel. This is calculated using the OBT calculations derived by Chris Long. http://the-long-family.com/optimal%20barrel%20time.htm

I've read the content at that link.

OBT is the mathematical explanation of OCW, as per the author.

The reason I would not use OBT instead of OCW remains.

A calculator is a model. The model requires measured inputs, subject to error. The model can only approximate the real world, some better than others.

Below the actual data as shot and QL predicting 0,2gr more to get to the node at 1.022ms. Practical accuracy and in the node band of normally 1gr in width. That is why I wanted to reverse engineer some of your data where you achieved accuracy. All the data used was from actual measurements and not a prediction.

TPL56mm Kriek 48gr 25gr Riflex RFL 3234vps gemeet Skote sny amper 25,2gr 3266vps

you guys are beyond my abilities.

Below the actual data as shot and QL predicting 0,2gr more to get to the node at 1.022ms. Practical accuracy and in the node band of normally 1gr in width. That is why I wanted to reverse engineer some of your data where you achieved accuracy. All the data used was from actual measurements and not a prediction.

TPL56mm Kriek 48gr 25gr Riflex RFL 3234vps gemeet Skote sny amper 25,2gr 3266vps

Your QL is showing only 93.28% propellant burned and 23.4 % ballistic efficiency with 91.3 fill

Not such a good load ? You are wasting propellant

I always try for close to 100% fill 100% propellant burned and upwards of 28 % ballistic efficiency
Granted this is very powder specific and normally happens with *MAX* loads

Below the actual data as shot and QL predicting 0,2gr more to get to the node at 1.022ms. Practical accuracy and in the node band of normally 1gr in width. That is why I wanted to reverse engineer some of your data where you achieved accuracy. All the data used was from actual measurements and not a prediction.

TPL56mm Kriek 48gr 25gr Riflex RFL 3234vps gemeet Skote sny amper 25,2gr 3266vps

Your QL is showing only 93.28% propellant burned and 23.4 % ballistic efficiency with 91.3 fill

Not such a good load ? You are wasting propellant On each load maybe 3gr. I have plenty of S321. Upping the charge will improve the % burn. This load was part of development and was used to show that OBT can give good predictions.

I always try for close to 100% fill 100% propellant burned and upwards of 28 % ballistic efficiency
Granted this is very powder specific and normally happens with *MAX* loads S335 did not give good results, whilst S321 works much better in my 223. That notwithstanding the poor % of burn. I do not intend spending thousands on a propellant that will give 100% burn.

S335 did not give good results, whilst S321 works much better in my 223. That notwithstanding the poor % of burn. I do not intend spending thousands on a propellant that will give 100% burn.

What is the price difference between SOMCHEM propellants and others ( imported ) ?

The only Somchem propellant in one of our LGS was S265. No primers to be found. Somchem used to be half the price of imported propellants. I believe S365 was about R100 cheaper lately.

The only Somchem propellant in one of our LGS was S265. No primers to be found. Somchem used to be half the price of imported propellants. I believe S365 was about R100 cheaper lately.

I believe the price ( unaffordability ) and unavailability of components is a bigger danger to the continued use of firearms in SA than any ham-fisted government action.

I have gradually become a believer in the OCW method. I find the predictions with GRT to be way off with some powders, and certainly not good enough to be used as a predictor of pressure or velocity on its own. But what GRT is good at, is when you fill in the barrel length, and you get the velocity for each node. That's where the fun begins. The caveat, is that without a chrony to check, GRT is useless. I am finding that from the rifles I have loaded for, my best groupings occur when the velocity corresponds to a node for that barrel length.

I have gradually become a believer in the OCW method. I find the predictions with GRT to be way off with some powders, and certainly not good enough to be used as a predictor of pressure or velocity on its own. But what GRT is good at, is when you fill in the barrel length, and you get the velocity for each node. That's where the fun begins. The caveat, is that without a chrony to check, GRT is useless. I am finding that from the rifles I have loaded for, my best groupings occur when the velocity corresponds to a node for that barrel length.

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Would you in your own words try explain the OCW method, there is something about it that I just do not click with - I just do not understand it.

I see it like this.

Imagine you are trying to shoot a target on a park swing that is moving.
If you aim for the target at the top of the upward swing when the object is momentarily stationary, and shoot when it reaches the top, then you have a much better chance of hitting than when the target is at the bottom of the arc of the swing when it is moving very fast.

If you get mathematical, and plot the speed of the swing on a graph as it goes back and forth, it will basically look like a sine wave. In other words, it slows as it reaches the top of the swing cycle and speeds up in between.

Now, when you shoot a bullet, the clever people (not me) figured out that it creates a wave through the barrel, and the tip of the barrel moves in a wave pattern, in other words, just like a swing, so if you release a bullet when the swing is up/ momentarily stationary, the bullet is released from the same point each time and the grouping will be good. If the bullet is released when the barrel is moving rapidly between stationary phases, the chances of the bullet being release from the same point each time is low, and hence the bullets are scattered around, and the grouping is poor.

Now, if you make the ropes of a swing longer, the swing will spend more time being almost still at the top of each passing, and take longer to get to the top of each side. It will also move at a higher velocity at the bottom/fast part of the swing cycle. In other words, changing the barrel length, is like changing the length of the ropes of a swing, and must be done for the OBT to work.

Now if you put it all together, it was a challenge for the developers of the theory to explain where the barrel will be moving fast and when it will be stationary, so they describe it (with whole lot of calculations I don't have a clue about) in terms of the time the bullet spends in the barrel before it is released, knowing that these times will correlate to points along the wave where the barrel is moving fast or is stationary. They called these "stationary" times where the barrel is hardly moving when the bullet is released, accuracy nodes, or Optimal Barrel Time (OBT). These barrel times equate to muzzle velocity or bullet speed. On a normal hunting rifle, the nodes are about 200ft/s apart.

So, if you have Gordon's Reloading Tool or Quick Load, and you can find the node # that fits within the pressure limits for that chambering that gives you a good fill % and powder burn rate with a specific bullet. Once you are there, load up a few tests either side of the predicted velocity. Go to the range, and see which test gives you that measured velocity (in the real world) and there you have it. The bullet should be releasing at the velocity where the barrel is predicted to be almost stationary, and therefor produce the best groups.

The other way of doing it, is the old fashioned way, where you shoot a ladder within the min and max velocities of the reloading guide, find your most accurate load, feed it into Quick Load, and suprise suprise, most of the time, your best grouping occurs at a velocity that equates with an OBT node.