OCW - Getting my head around it


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chocdog
June 16, 2012, 01:55 AM
Hey all,
I have doing OCW's for my 30-06. So far I have completed the initial tests for 150, 165 and 180 SGK SPBT using RE15, RE19, RE22 and Varget. I have used On Target to plot my groups and I am trying to interprete the data. This is where I think I am lacking. According to what I have read on Dan Newberry's site, I am to look for a 3 groups that have the same approximate group center and the OCW should be the one in the middle and that would be the load to further develope.

:confused: My questions are as follows.:confused:

- I have several tests that have more than 3 groups with close approximate centers. In that case what would be the OCW?
- What is an acceptable approximation when comparing centers? 1/8" 1/4" 1/2"?
- I have read from quite a few sources that 3 shots are not statisically enough to determine a good grouping, 5-7 have been recommended. How many shots do you use?
- My goal is to work up a accurate and repeatable hunting load. So am I wasting time, money and materials making multiple loads on the light end as instructed? Or should I only load the light end in singles to check for adverse pressure and use the loads that have the desired velocity and KE for the OCW?
- Do you even use the OCW or ladder method, or do you pick a load soley on velocity and KE and go from there?

Any help would be greatly appreciated.

Thanks in advance!:D

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USSR
June 16, 2012, 09:44 PM
My goal is to work up a accurate and repeatable hunting load. So am I wasting time, money and materials making multiple loads on the light end as instructed?

Yes, and that is what I told Dan 10 years ago on another site. All I do is load up 3 rounds at the midway point between a starting and maximum charge weight and then vary all my other 3 round groups by .5gr, right up to the maximum listed charge weight. Then, at the range I start with the lowest charge weight rounds and run them over my chronograph looking for the velocity I expect and not even checking them for accuracy. Oh, and you will make use of your bullet puller. ;) Once I have a feel for the approximate charge weight that puts me where I want to be velocity-wise, I go back to the loading bench and load 3 or 4 groups of 5 cartridges, varying each group by .3gr. This time I am looking for accuracy. Why do I do this? There are several accuracy nodes that can generally be found when reloading, and it makes zero sense to me to find an accurate load at a velocity level that I am not satisfied with. Just MHO.

Don

Kachok
June 16, 2012, 11:27 PM
I load three rounds of each bullet powder combination in three separate powder charges, so 9 rounds total for that bullet. 1 set at starting load, 1 set at mid and 1 set at max. If I get .75 MOA or better with one of those groups then I will tweek with slightly higher or lower charges, different primers, and different COL. This might not be the textbook way to do it, but it has really worked for me, mabey I am just lucky. No need for five or seven round groups when doing the rough cut work, though there is some virtue in it once you get to the fine tuning of the load. I had a rough cut load shoot a perfect one hole group yesterday, no kidding 1st group I ever fired with that bullet. The Nosler #6 Manual lists the most accurate loads they tried, and often those are a good starting point to tweek from in my experience.

kingmt
June 17, 2012, 10:40 AM
Why max? What reason are you controling volicity? Do you understand how your bullet works?

KE has little meaning in something as small as a bullet compared to something the size of a deer. It does have a barring on the bullets expansion. KE controlled with expansion is what I'm looking for.

It depens on what reason I'm loading the ammo. If I want thight groups then I don't care how fast it is going when it gets there except I'm selfish with powder. If it is hunting ammo I have a idea of how I want the bullet to act in the body & from playing with the bullets I have a pretty good idea what is going to happen.

I also only use 3 shot groups when doing the rough work or 1 if looking for jacket sepration. If 3 go in the same hole & the charge above & below it look about the same then that is good enough for me. If nothing in the group is close then I don't mess with that ether. A bullet down range is never a waste to me. I enjoy shooting so much I can be happy watching someone else shoot like others watch ball games.

Trent
June 17, 2012, 12:36 PM
Shooting at targets incrementally or sequentially makes no difference. You're equally likely each time you pull the trigger to do something that adversely affects the shot.

I shoot 10 shot groups, make sure I'm zeroed. Then shoot 10 shot groups for testing.

3 or 5 shot groups are statistically INSIGNIFICANT, even if you do them sequentially. You need a larger sample size to determine standard deviation - the only TRUE metric of performance.

The guy that developed OCW needs to take a deep course in statistical mathematics. and rethink his theories.

beatledog7
June 17, 2012, 01:46 PM
OCW is just one initial away from OCD. Just saying....

chocdog
June 17, 2012, 02:53 PM
OCW is just one initial away from OCD. Just saying....
Isn't reloading by nature OCD?

1858
June 17, 2012, 03:42 PM
chocdog, I've been using the OCW method for a number of years now and shoot five-shot groups in a "round-robin" approach. I like the method that Don uses to quickly find the desired velocity range and then refine the load. If you have more than three groups with similar group centers (shown as Off H: x.xxx", V: y.yyy" using OnTarget) then you could simply add up the charges and divide by the number of loads to get your "center" and then add and subtract by some value e.g. 0.3gr and confirm that you have the OCW.

Like Don, I start off by getting into the velocity range that I want. I always want the fastest velocity possible so unlike Don I don't start midway between the min and max published data. I start about 25% closer to the max published load.

Kachok
June 17, 2012, 05:19 PM
Is there any OCW calculator for oddball length barrels?

chocdog
June 17, 2012, 06:02 PM
1858
Thanks for the info.

1858
June 17, 2012, 06:13 PM
chocdog, I've found that OCW loads for a particular rifle also shoot extremely well in other rifles ... easily under MOA and often closer to 1/2 MOA.

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