Calling all OCW experts

OCW?

Aaaaahhhh, thank you!

That one was not included in the Acronym list Sticky Thread in the first forum ... and all of the Possibles that I was coming up with were just Silly.

Personally, I don't view any difference between a ladder test and an OCW, other than chest thumpers saying they are different.

In general, I never compile the shots into one target as you have without running them all side by side and watching the "wave motion response," meaning how the group centers shift in response to the changes in powder charge.

Here's an OCW assessment I did for another user on another forum a while back. I'm working from my phone right now, otherwise I would do the same for your targets. Note the aiming points are all lined up on the red line, then the centers of the groups are traced by the yellow line. You want to pick your target charge weight from a region of the yellow line which is relatively flat/stable/not wavy. It does not matter where the groups hit relative to the aiming point, so it's ok if it's above or below the red line, it only matters if the yellow line is flat. Assessing this users targets, he should be loading somewhere between #5 and #6, as 4-7 is the flattest region of the wave.

But as always - 3 shot groups are ALMOST meaningless.

Knowing 4-shot group sizes and centers can vary a lot (3 to 4 times) across several with the same load, I consider those equal.

I disagree with that muzzle enlargement from shock wave causing problems. Four Garand barrels with the rifling and groove diameters enlarging .002" and no copper wash the last half inch still shot sub MOA at 600 yards. Wear from cleaning rods rubbing metal away.

If that were true, then all 24" barrels would have the same set of barrel times for all bullets. And the same load that did well in a 22" barrel would not do well in a 25" one. Yet the same load in commercial match ammo shoots sub MOA across 6" of barrel length spread.

How do you separate your variables from those of the rifle and ammo?

OCW is a myth.

Bart - if you mistakenly interpreted my use of the word "wave" to refer to bore diameter deflection, read my post again, as I did not say anything at all about shock waves. Otherwise, I'm not sure why you brought it up at all?

OCW largely agrees with many of the posts you have made, especially recently about a band of powder charges which will not change POI.

tcoz said:

If OCW is a myth and you're limited to a 100 yard range, how would you do a load test? I would think I should just look at the group sizes on my targets in that case.

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I used to be like you. I was deluded into thinking I could find the perfect load in under 20 rounds. Eventually I found that there are a few courses of action to take during load development. You can shoot few rounds and convince yourself that the smallest group is indicative of future outcomes. You can piggy-back on known accuracy loads with a measure of success. You can shoot a ton of ammo and just let the data speak to you.

I will tell you one thing though, Bart B. seems to get smarter the more you shoot. It's almost like he knows what he's talking about but I'm not quite sure, I still have more shooting to do.

tcoz said:

Orcon, here's the thing. I'm not looking for the perfect load. I'm working within the limitations that I have. I live 45 minutes from the range (100 yards) and I'm lucky to be able to get there twice a month. When I do go, I can't be gone longer than 3-4 hours because I'm the caregiver for my wife with a chronic medical condition and I can't leave her alone for more than that amount of time. I don't want to spend six months trying to work up a load the good old fashioned way so I try to do it as expeditiously as I can within my limits. That's why the OCW method appeals to me, plus the theory behind it fascinates me.

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I think one may interpretation of the given feedback has nothing to do with 100 yd range, it's putting more lead downrange. Shoot more bullets into your group at 100 yds.

The OCW wave is the firing shock wave going back and forth in a rifle barrel at the speed of sound in steel. It makes a few round trips before bullet exit. It does obturate bore diameter at the muzzle a few or several millionths of an inch.

I never worked up any load for an existing bullet for any cartridge. Just used what worked best across many others; same load across several barrel lengths and powder lots.

To test at any range, shoot at least 20-shot groups per load. Never ever pick the smallest 3- or 5-shot group of several as "the" one to use.

I'm not a subscriber to the OCW method, in whole or even in part really, but for wildcat cartridges I have owned, it's a damned good start when known data is sparse, or non-existent.

Bart - the "wave" I referred to, reiterating here, is the sliding yellow line across the picture I posted. Whether that disparity is only caused by obturation of the crown at the moment of release or not doesn't matter, because the travel of the supersonic "shockwave" is NOT what I was talking about in my post.

In your own response in the thread on working up a load for 243win, you state a shooter should be able to find a charge weight window of 3/10ths of a grain which won't dramatically affect POI. If you're standing on the shoulders of giants to come up with known loads, then great. I largely do the same - I find loads which are proven, and work from there. But whenever you do any wildcatting, play with new powders, or new bullets, in other words, when known proven loads don't exist, what are you supposed to do other than load development? How else do you find that charge window where 3/10th doesn't make a difference?

As I stated above, 3 shot groups are meaningless, so on that we completely agree. At it's core, however, OCW doesn't care about group size. Only where the groups print on the page. Number of shots should be large enough to suss out the difference between centers, which is at least 10 shots, the more the better.

The OCW theory isn't about finding the smallest group, it's about finding the load with the most tolerance to small reloading errors. The idea is that you should be able to find a powder charge that doesn't require you to sit for hours at the reloading bench trickling powder charges and making the cases perfect so you can spend more time at the range.

OCW tests typically use 3-shot groups.

Using the same statistical reasoning, one can therefore determine the number one and a half pair of dice will always be by one throw of all three cubes with their flats numbered 1 to 6. Get several 3-die sets then throw each set once. Choose the set that gives the number from 3 to 18 you think is best.

Or just roll each die among several 3 times then pick the die that gave the number you want.

Maybe it's in the way your looking at it. Instead of a 3 shoot group think of it as a 9 shoot group that the spread in the charge is as much as .6gn. it's just shoot into 3 different targets then stacked to decide where center of the centers are. Then you can see how big of a group your centers are plus your total group is.

This still isn't a finishing place. It's just somewhere to start with if you want to keep working on it or forget it & move on to something else.

The biggest problem with 3 shoot groups is what if you have two flyers in the same group. This isn't as likely with good bullets but it is with FMJ or worse pulled bullets. When there isn't any data to piggy back then I often shoot 3 at a time to figure out where I want to start trying to make a load. That doesn't mean I won't go back & try something else at any point.

From the OP's pictures 41.8-43 all look like they are fallowing the same suit. I'd go back & shoot 5 shoot groups now to see if I wanted to keep working them. Looks like 42.5 might be a good targeted load but only time will tell.

I've been using this lately. It makes sense to me. The OCW method doesn't

http://precisionrifleblog.com/2012/07/13/creighton-audette-ladder-testing/

Varminterror said:

Personally, I don't view any difference between a ladder test and an OCW, other than chest thumpers saying they are different.

In general, I never compile the shots into one target as you have without running them all side by side and watching the "wave motion response," meaning how the group centers shift in response to the changes in powder charge.

Here's an OCW assessment I did for another user on another forum a while back. I'm working from my phone right now, otherwise I would do the same for your targets. Note the aiming points are all lined up on the red line, then the centers of the groups are traced by the yellow line. You want to pick your target charge weight from a region of the yellow line which is relatively flat/stable/not wavy. It does not matter where the groups hit relative to the aiming point, so it's ok if it's above or below the red line, it only matters if the yellow line is flat. Assessing this users targets, he should be loading somewhere between #5 and #6, as 4-7 is the flattest region of the wave.

Click to expand...

If you think of the OCW process as a way to find the most accurate load rather than the most precise load then the concept makes more sense ( accurate being defined as how close the group centers are to the point of aim while precision is how close each impact is to the other impacts). Your graphic demonstrates that concept perfectly. Most shooters fail to differentiate between the two concepts and end up chasing their tail while developing a load.

Nature Boy said:

I've been using this lately. It makes sense to me. The OCW method doesn't

http://precisionrifleblog.com/2012/07/13/creighton-audette-ladder-testing/

Click to expand...

If you take out range and shot count, OCW and Ladder tests are effectively the same, only one typically uses coloured bullets to identify strike points against one POA and the other uses individual aiming points for each charge. Lots of guys shoot OCW at 300yrds, lots of guys shoot Ladders at 100, and equally, lots of guys shoot more or less shots within each charge, so the only fundamental difference is the number of aiming points.

So many guys doing OCW convert their targets, as tcoz did in his second picture, to a single POA ladder target. At that point, the analysis is really the same either way.

Similarly, most guys shoot these over a chrony - and of course, what does a chrony tell you in 3 shots??? - as in the old article linked. Without knowing your SD and ES at each powder charge, meaning without a sufficient round count, a plot of velocity vs. charge weight is largely meaningless, as the velocity changes may not be statistically significant.

Both are nothing more than a test of elevation change per powder change. OCW guys criticize that the Ladder takes too many shots and requires a 300yrd range, and Ladder guys criticize the OCW test doesn't use enough shots and doesn't fly far enough to spread the groups. "Fix" either criticism about either test and you end up shooting the other, meaning if you do either "correctly," you end up at the same test.

One other aspect worth noting - for cartridges where known proven loads don't exist, major detractors cite the extreme round count required to develop loads with either method. If you work up 3 or 4 powders with either test, especially if you shoot statistically significant 10 shot groups (or more), that's somewhere north of 150-200 shots. In a cartridge with a barrel life around 1,500, most guys don't want to burn that much life just in development.

But as Bart has pointed out, once you find a qualifying load, it will typically perform well in many rifles, regardless of barrel length. So even though it might cost you half of your first barrel, most of the time the same load will suit you well in every barrel thereafter. So then barrel replacement simply becomes the cost of doing business.

tcoz, since you have limited time and seem to like this method it would probably help if you use the OCW method but with at least 5 rounds over 3. That would not add a lot of time to your range trip.