My first attempt at OCW load development

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doowroh

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I'm working on loads for two different rifles, two different calibres and two different projectiles each.

.243 Win. 70 grain Nosler Ballistic Tip
.243 Win. 85 grain Sierra HPBT GameKing

.308 Win. 168 grain SMK
.308 Win. 175 grain SMK

OCW = Optimal Charge Weight (re: Dan Newberry)
Being my first attempt at this concept in load development, I've learned that the goal here is to determine the most *consistent* point of impact as opposed to the smallest group size. So here are some of my targets, and my thoughts on which I'd pick for the OCW. I'd love to have your thoughts as well.

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For the 70 Nosler BT over IMR-4064, I'd pick 39.4 grains as my OCW.


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For the 85 SGK over IMR-4350, I'd pick 40.9 grains as my OCW.


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For the 168 SMK over IMR-4064, I'd pick 42.8 grains as my OCW.


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For the 175 SMK over IMR-4064, I'd pick 42.4 grains as my OCW.

Thanks for looking.
 
I don’t get how you chose what you did. To me there’s better choices? Am I missing something? Like in first set. How is 39.4hr better than the 39.8?
 
I get what you are saying, but the (Dan Newberry) methodology for his Optimal Charge Weight (as I understand it) is not to choose the smallest group, but to find a "node" where three distinct (like, 3 steps of increased) powder charges end up with the same (or as close to the same) point of impact. That way, with future hand loads, any variances in charge weight or ambient temperature or barrel/chamber heat should get you the same point of impact on target. You'd pick the "middle" of the three that have consistent POIs.

Then you tune for accuracy with seating depth, etc.

Again, that's at least how I understand **THIS** method of load development.
 
I think you are roughly right. But don't you need many more loads at smaller increments? I thought people that do this loads one round each with 0.1 grain increments and like 20 incremental loads. You need to be able to pick out a pattern of oscillation, and to resolve a pattern you need way more data points than 6.
 
I should also mention that some fundamental concepts regarding signal to noise and statistical significance should be considered here. If your group sizes are 3", and you are firing 3 shots per group, and the center of the group is moving 2", then I would suggest that there is no actual 'signal' or real data coming from the 'motion' of the center of group because the per-shot variance at the same load is higher in magnitude.

Then this further complicates because I think some people do this same concept of finding a node by firing successive incremental charges, but ignoring the impact location and only using the speed of the bullet. Here's an example of that from the internet:
https://ultimatereloader.com/2018/02/18/expanded-10-shot-load-development-for-6-5-creedmoor/
Chart-50-Shot-load-development-crop.jpg
 
That’s how I have done it before. Chronograph and single shot and then find the OCW that way and then go to seating depth.
 
I'd really be looking at working around 41.1gr of 4350 with the 85gr Sierras.

I don't really see anything I like with any of the others. Maybe work around the one Ganderite picked out as well, but if it doesn't work out, its back to the drawing board with the .308 loads.
 
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