Understanding OCW Testing

G

gnfiter3

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Full Member
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May 28, 2007
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Florida
#1
I'm just beginning to understand this concept. Here's the question. If I work a load up in .5 grain increments, and get the tight group I want from a given load and bullet weight, will that load eventually equal the results I would get from an OCW test?

Not sure they don't take the same amount of time, but the results seem to be the same.
 
#2
Re: Understanding OCW Testing

OCW is more to do with finding the best time ( in the barrels vibration )for the bullets to exit.

How well your found load will react to temp variations can be interesting, this is what the OCW addresses.


Like the author, I have also found that once the median charge is found ,the group sizes are very acceptable.

For my rifle OAL adjustments were not necessary above 2.800 (.308 ,175 SMK, 43.5gr Varget, Lapua. )
 
#3
Re: Understanding OCW Testing

Well, I got that bullet exit point with respect to the vibration and/or barrel harmonics. It just seemed that if the selected load gave me the group size I was looking for, then I have also,or just may be, in the range of the resulting OCW parameters?

Are you suggesting that if there's a major temperature, altitude or other atmospheric change, that the load will not perform as well, as a load selected from the resulting OCW results?

Wil, from Tx; this sounds like another one of those organized record keeping things you seem so good at?
confused.gif
 
#5
Re: Understanding OCW Testing

Correct, if atmospheric condions change then the POI may be drastic.

The load you have found may only be good for those conditions.

It is possible that load is in the range OCW range, but if no loads of varing charge wieghts were plotted, one truely does not know where the median charge is.

Dan Newberry states not to look at the group sizes, just the group locations.

When I would run this exercise there would be some groups that were half MOA,but later found to be out of the OCW range.

It's hard not to get side tracked by this useing traditional group size thinking.

Once the impacts were plotted and median charge was found it all makes more sense.
 
#6
Re: Understanding OCW Testing

I checked it out. Darn, now I have to go shoot up all those incremental loads and start again
grin.gif
As I told a friend who is not into shooting or loading; it's a science. I will pursue the OCW load development program, just because it's interesting. I don't have a lot of environmental changes to worry about down here. The only way to get 500' ASL is to climb a tower

Funny, as I read the comments on RL-15, above 90 degrees. It's routinely that hot here 5 months a year. Fortunately, the only local range is covered, so it can't cook? Then it cools to the mid to high 80' and cold is anything below 55. I just got some RL-15, and fortunately, a South Fl. winter is in the 60's and low 70's. It'll all be gone before it gets hot here again. Perhaps by then, the Varget shortage will be over. I do like the way it meters.

This forum is like going to school, but loving it!
 
#7
Re: Understanding OCW Testing

For me the OCW test is means to and end.
I don't want to chase unicorns, just find a sub MOA load and go shooting.
The OCW has exceded my requirements as half MOA results are possible if/when I get myself squared away.

Florida hot ?
crazy.gif

The <span style="text-decoration: underline">only</span> thing I miss is the beach.
I recentlly went back to S.FL. after 17 years and could not recognize anything.

have fun
 
#8
Re: Understanding OCW Testing

OCW is a charge weight that shoots good and impacts in the same spot despite variances. For example, an OCW of 45 grains of Varget under a 168gr Amax shoots the same as 44.8 grains or 45.2 grains. So if you set your crappy powder measure to throw 45 grains, your load will shoot well even if the measure throws charges all over the place.
 
#9
Re: Understanding OCW Testing

918v, yeah like trying to throw varget in my 550. That alone would make OCW a plus. It throws ok, but it cound be +/- .30.
I like what Dan said about, if you think your load is all that, throw 1% +/- that weight and see what happens.

Back to school and back to the bench.
 
#10
Re: Understanding OCW Testing

I'm still really trying to get my head around the OCW thing. I tried one sample string at the range a few weeks back with mediocre results but I don't think I had enough load steps to get an accurate sample. I'm not trying to defend the ladder method, just trying to understand the differences and why OCW is better.

Here're my two questions:
1) how does shooting round robin style differ from doing a ladder test in what results it gives you? For instance, if I shoot the ladder exactly like I do the RR, i.e. 3 or 5-shot groups with 2 min spacing between each shot at the same target. How is that going to give me different results than if I do the exact same thing with the exact same loads, but shooting one at each target at a time? You still end up with a group of 3-5 shots of the same load on the same target.

2) I guess I'm still confused as to how the ladder and the OCW differ in what its telling you. If I shoot a ladder (again assuming 2 min spacing between shots), and I see the groups gradually close down and then open back up again as I find the accuracy node - is that not telling me the best group is where the barrel harmonics are optimum for that load?
 
#11
Re: Understanding OCW Testing

It works better because it allows you to see changes in POI sooner than you would have shooting five-shot groups. That way you waste less in developing your load.
 
#12
Re: Understanding OCW Testing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">I'm still really trying to get my head around the OCW thing. I tried one sample string at the range a few weeks back with mediocre results but I don't think I had enough load steps to get an accurate sample. I'm not trying to defend the ladder method, just trying to understand the differences and why OCW is better.

Here're my two questions:
1) how does shooting round robin style differ from doing a ladder test in what results it gives you? For instance, if I shoot the ladder exactly like I do the RR, i.e. 3 or 5-shot groups with 2 min spacing between each shot at the same target. How is that going to give me different results than if I do the exact same thing with the exact same loads, but shooting one at each target at a time? You still end up with a group of 3-5 shots of the same load on the same target.

<span style="color: #3333FF">You are essentially doing the OCW, by using more data for each representitve load
However, the difference is better explained in your next question.</span>

2) I guess I'm still confused as to how the ladder and the OCW differ in what its telling you. If I shoot a ladder (again assuming 2 min spacing between shots), and I see the groups gradually close down and then open back up again as I find the accuracy node - is that not telling me the best group is where the barrel harmonics are optimum for that load? </div></div>

<span style="color: #3366FF">The traditional ladder test that Dan cites, there is one shot per load.
Keep in mind in OCW you are looking at POI not group sizes.
Group size has little to do with OCW, think of it as a finishing step with the actual test the rough.</span>
 
#13
Re: Understanding OCW Testing

One of the things discussed on Dan's site is that in a conventional ladder test, barrel heating, fouling, and just plain shooter error are not distributed evenly across the string. You can mitigate that somewhat by controlling the time between shots, but with an OCW test, all charge increments tested get the benefit/abuse of a hot, dirty barrel. And you get three chances to hose each group and skew the results, not just one shot per increment as with ladder testing
wink.gif
 
#14
Re: Understanding OCW Testing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">I'm still really trying to get my head around the OCW thing. I tried one sample string at the range a few weeks back with mediocre results but I don't think I had enough load steps to get an accurate sample. I'm not trying to defend the ladder method, just trying to understand the differences and why OCW is better.

Here're my two questions:
1) how does shooting round robin style differ from doing a ladder test in what results it gives you? For instance, if I shoot the ladder exactly like I do the RR, i.e. 3 or 5-shot groups with 2 min spacing between each shot at the same target. How is that going to give me different results than if I do the exact same thing with the exact same loads, but shooting one at each target at a time? You still end up with a group of 3-5 shots of the same load on the same target.

2) I guess I'm still confused as to how the ladder and the OCW differ in what its telling you. If I shoot a ladder (again assuming 2 min spacing between shots), and I see the groups gradually close down and then open back up again as I find the accuracy node - is that not telling me the best group is where the barrel harmonics are optimum for that load? </div></div>

The Round Robin shooting order helps "average out" other variables in addition to the barrel heat factor, such as fouling, changing atmospheric conditions during your test period, etc, which could affect the results. You could do the OCW method (or any other load development method where you should groups with different loads) without shooting in Round Robin order, your results would just be more prone to being influenced by factors outside the load itself.

The big conceptual difference between OCW and other methods is that you ARE NOT looking for group size during the powder charge phase -- you are looking for the smallest change of average vertical point of impact between consecutive powder charges (if you are looking at group size during the powder charge phase, you aren't doing OCW). As previous posters have explained, what you are trying to find is the most "stable" powder charge (and the result, in my experience, tends to be really consistent velocities, even when temperature variations, etc aren't a concern).

Often for me, the eventual OCW powder charge often isn't the best grouping load in the initial OCW phase -- the really nice groups comes in phase two when you monkey with the seating depths after establishing said powder charge. I've never had an OCW powder charge not group really nice after monkeying with the seating depth.
 
#18
Re: Understanding OCW Testing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gnfiter3</div><div class="ubbcode-body">mattj: Do you or have you done an OCW and found the OAL for the best load is longer than mag length. That would be a bummer for me with an AR.</div></div>

Sorry, just saw your question -- I honestly can't really say as my rifles can all be loaded to touch the lands and still fit in my mags (and I don't have any experience loading for the AR). I imagine if you use a jump-tolerant bullet like the SMK that you'd be just fine. I know there are highpower service rifle guys that use OCW.
 
#20
Re: Understanding OCW Testing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattj</div><div class="ubbcode-body"> <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gnfiter3</div><div class="ubbcode-body">mattj: Do you or have you done an OCW and found the OAL for the best load is longer than mag length. That would be a bummer for me with an AR.</div></div>

Sorry, just saw your question -- I honestly can't really say as my rifles can all be loaded to touch the lands and still fit in my mags (and I don't have any experience loading for the AR). I imagine if you use a jump-tolerant bullet like the SMK that you'd be just fine. I know there are highpower service rifle guys that use OCW. </div></div>

I did a work up with my AR30 in .338LM. The SMK's are off the lands by quite a bit in order to magazine feed. However, I wound up with a .363" 5-shot group at 100.
 
#21
Re: Understanding OCW Testing

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gnfiter3</div><div class="ubbcode-body">Darn, now I have to go shoot up all those incremental loads and start again</div></div>
With OCW, you'll use your incremental loads.
 
#23
Re: Understanding OCW Testing

Here is the key its vertical spacing not grouping , this is what I misssed the first time I tried it
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattj</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">I'm still really trying to get my head around the OCW thing. I tried one sample string at the range a few weeks back with mediocre results but I don't think I had enough load steps to get an accurate sample. I'm not trying to defend the ladder method, just trying to understand the differences and why OCW is better.

Here're my two questions:
1) how does shooting round robin style differ from doing a ladder test in what results it gives you? For instance, if I shoot the ladder exactly like I do the RR, i.e. 3 or 5-shot groups with 2 min spacing between each shot at the same target. How is that going to give me different results than if I do the exact same thing with the exact same loads, but shooting one at each target at a time? You still end up with a group of 3-5 shots of the same load on the same target.

2) I guess I'm still confused as to how the ladder and the OCW differ in what its telling you. If I shoot a ladder (again assuming 2 min spacing between shots), and I see the groups gradually close down and then open back up again as I find the accuracy node - is that not telling me the best group is where the barrel harmonics are optimum for that load? </div></div>

The Round Robin shooting order helps "average out" other variables in addition to the barrel heat factor, such as fouling, changing atmospheric conditions during your test period, etc, which could affect the results. You could do the OCW method (or any other load development method where you should groups with different loads) without shooting in Round Robin order, your results would just be more prone to being influenced by factors outside the load itself.

The big conceptual difference between OCW and other methods is that <span style="color: #FF0000">you ARE NOT looking for group size during the powder charge phase -- you are looking for the smallest change of average vertical point of impact between consecutive powder charges </span>(if you are looking at group size during the powder charge phase, you aren't doing OCW). As previous posters have explained, what you are trying to find is the most "stable" powder charge (and the result, in my experience, tends to be really consistent velocities, even when temperature variations, etc aren't a concern).

Often for me, the eventual OCW powder charge often isn't the best grouping load in the initial OCW phase -- the really nice groups comes in phase two when you monkey with the seating depths after establishing said powder charge. I've never had an OCW powder charge not group really nice after monkeying with the seating depth. </div></div>
 
#24
Re: Understanding OCW Testing

You are still looking at group sizes in OCW, you are just not working to tighten the group up in the first phase. This from Dan's site:

<span style="font-style: italic">"I show all of the targets above because <span style="color: #000099">I want to illustrate the importance of the "scatter group."  This will be one group of the round-robin sequence that seems to inexplicably open up. The reason for this? The Shock Wave, as identified and described by engineer Chris Long in the page linked above, is at the muzzle when those bullets are being released. Generally, a 1 to 2 percent powder charge increase above the scatter group charge weight will have you right in the OCW zone.</span>

But the real reason I wanted to discuss the scatter group is this: Please note that in each of the scatter groups shown above, ONE shot lands right on the same POI (or within 3/8 MOA or so) as the groups preceeding and proceeding it. This means that in at least one of three instances, during a conventional Ladder Test, the target would indicate a wide "sweet spot" where it should not. The OCW round-robin testing easily identifies the problem with this charge weight level, but in (at least) one of three instances, the Ladder Test will miss it--which may lead a shooter to an incorrect conclusion as to the center of the true accuracy node.

Sure you can go back and prove and re-prove your Ladder Test results--but if you'll take the time to understand the OCW/round-robin firing sequence, you'll not have to do any such re-proving; you can move right on to depth tuning (adjusting the seating depth of the bullet for absolute accuracy)."</span>

http://optimalchargeweight.embarqspace.com/#/ocw-vs-ladder/4529811360

You are looking for your 3 most consistent groups between 2 scatter groups. You pick the middle of the 3 and then go to seating depth to tighten up. This test is NOT ladder testing and Dan never talks about looking for vertical stringing.

When you lay your targets out like a time line, you can read your barrel harmonics like a book. You can see exactly when your barrel opens up (shock wave at the muzzle/scatter group).
 
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