OCW method - second rifle test

[big5ifty]

Because I was able to achieve what I consider to be a good result with my first OCW test, I tried the same test on a second target rifle.

This is a 375 RUM, using 300 grain Peregrine Rangemasters, with N570 and Federal 215 Match primers.









Again, I have a full two percent spread where the group centers are almost identical. 102, 103 and 104 grains. The left-most shot on the 102 is indicative of a pulled shot - Dan Newberry says if the flyer is not in the direction of the previous or next charge weight group center, it's a shooter induced error.

I will re-shoot this at 102.5, 103 and 103.5 to verify that the group centers remain the same. If that works out, I can work on the seating depth.

It's been very interesting for me to see the OCW test in action, and get what seems to me to be a conclusive result.

[Tripodmvr]

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]

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.

[Tripodmvr]

What distance was the chrony at?

[Treeman]

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.

[big5ifty]

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 .

[big5ifty]

What distance was the chrony at?

5 meters. Most likely too close.

[Treeman]

5 meters. Most likely too close.
[/quote]
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There I was thinking I was overdoing it a tad, 5 m + then ?   

[Tripodmvr]

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?

[big5ifty]

What barrel length does the 375RUM have?

30"

[Treeman]

What barrel length does the 375RUM have?

30"

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

[big5ifty]

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.

[DaavG]

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?

[big5ifty]

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.

[big5ifty]

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

3" splatter target