OCW method - second rifle test

[DaavG]

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?

[Tripodmvr]

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.

[big5ifty]

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.

[Tripodmvr]

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.
[/quote]

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.

[Tripodmvr]

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

[big5ifty]

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.

[Tripodmvr]

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

[Treeman]

you guys are beyond my abilities.

[Newton]

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

[Tripodmvr]

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.

[Newton]

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 ) ?

[Tripodmvr]

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.

[Newton]

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.

[Againstthegrains]

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.

[Treeman]

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.