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Why does OCW have to be at 100 yards

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#4
I don't think it has to be. But like almost everything else rifle related in this country, the default is 100 yds (lowest common denominator).
 
#6
OCW was developed for those who don't have the ability to test results at long distance. It's meant to be a predictor of whether a load will do well at distance, rather than the actual "correct" answer.
 
#7
I initially start my OCW tests at 100 yards, I then move back to 200 yards and so on after the initial tests... It has worked for me. But it really helps because the closets range is only 200 yards, otherwise it's 2 hours plus to get past that.
 
#9
Or if you have a good chronograph like a magnetospeed or labradar, then you don't even need a target. You just load in .2 grain increments and look for the velocity flat spots. It's doing the same thing as an OCW, just in a different way.
 
#10
What is the difference at 50 or 75 rather than 100. Especially, if wind is a factor. We measure groups angular so what would be the difference, anyways?
 
#11
The ocw goal is to see where the groups shift in relation to one another and find a spot where higher or lower charges don’t alter the point of impact. I’m sure if you had a good enough shooting gun you could do it closer but at 50 yards I imagine that the actual size of the group is larger than the shifts that we are looking for in many instances. When I’ve done the testing myself the groups seem to shift about an inch up or down, left right etc. At 50 yards that would be 1/2” of shift when scaled but my groups probably won’t be tight enough for me to be able to separate the shift from the group. Might be easier with a 22 cal vs.a 30 cal. Software might be much more useful up close as well.
 
#12
It doesn't have to be at 100 yards and if you are doing load development for long range such as F Class you are better off testing at longer ranges. One theory is that you should test at the ranges you will be shooting. In F Class this is typically 600 and 1000 yards. The problem is that atmospherics can skew your results and sometimes best to use a distance where you can easily discern the vertical dispersion of various loads. Different loads should be chronographed so groups can be compared against ES and SD.
 
#13
ZiaHunter said:
It doesn't have to be at 100 yards and if you are doing load development for long range such as F Class you are better off testing at longer ranges. One theory is that you should test at the ranges you will be shooting. In F Class this is typically 600 and 1000 yards. The problem is that atmospherics can skew your results and sometimes best to use a distance where you can easily discern the vertical dispersion of various loads. Different loads should be chronographed so groups can be compared against ES and SD.
Click to expand...

Atmospherics aren't going to induce vertical dispersion over the short amount of time that it takes to perform an OCW. In this context group dispersion due to wind can be ignored.
 
#14
MachoKing said:
Or if you have a good chronograph like a magnetospeed or labradar, then you don't even need a target. You just load in .2 grain increments and look for the velocity flat spots. It's doing the same thing as an OCW, just in a different way.
Click to expand...

Yea that would be the most efficient way, collect data and plot at home.
 
#15
Ive always done mine at longer ranges. 530 yards typically, because it’s an east spot to place a target at my desert shooting site. I’ll reduce that for short range cartridges. I use a common bullseye and mark the bullets in each load with a different colored sharpie, so I can sort them out later.
 
#17
308pirate said:
Atmospherics aren't going to induce vertical dispersion over the short amount of time that it takes to perform an OCW. In this context group dispersion due to wind can be ignored.
Click to expand...

I should have clarified my comments. Testing at longer distances will provide a better indicator of vertical dispersion but wind can impact group size during the course of testing.
 
#18
As MachoKing said, OCW is only looking for velocity flat spots which it measures indirectly by vertical dispersion. If you have a good chronograph you can measure it directly and you don’t need a target at all. The key here is that all shooter (human) error is removed. This is the method I’ve started to use since I got a MagnetoSpeed and it works well for me.
 
#20
Y’all need to go reread the ocw methodology as chronographs only aren’t it. Looking for flat velocities isn’t necessarily going to yield great groups. Not to say that it doesn’t have its merits, it’s just not an ocw.
 
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#21
tscoz said:
As MachoKing said, OCW is only looking for velocity flat spots which it measures indirectly by vertical dispersion. If you have a good chronograph you can measure it directly and you don’t need a target at all. The key here is that all shooter (human) error is removed. This is the method I’ve started to use since I got a MagnetoSpeed and it works well for me.
Click to expand...

This is only partially correct. OCW is looking for more than velocity flat spots. It is also looking for ignition impulse and its effect on barrel harmonics. This has been covered in the past and unfortunately I am no expert on it to get into much more detail. It is very possibly to find a velocity flat spot that it also in the scatter node area for your barrel/load combination.

This is not to say that OCW is the only way to find a good load, as anyone that's been doing so for a while knows that there are a few good ways to skin this cat. Read up a bit more on OCW and you'll find that one of the reasons that it is done at 100 yards is to provide a good method for finding a good forgiving load, for the many shooters that do not have convenient access to longer ranges.
 
#22
You may be right. Every time I chronograph a load they are consistent with ES in the 20s and SD 7-10. This is why I usually just find the max load and back off .5 grains. I was just curious why people use 100 yards or greater for OCW when theoretically you would get the same or better results at shorter distance for the initial OCW data.
 
#23
The only issue with doing it at shorter distances, like already mentioned, is that quite often, the differences between vertical distribution for the various round robin three shot groups is often very small. To support that, take a look in this section where quite often posters ask for help to determine what the nodes are on their OCW test.

Shooting it at shorter distances would make it even more difficult to positively identify a good node, IMO.
 
#24
The 6.5 Guys have been using the chronograph method with great success. Why do three groups in an OCW impact the target in the same spot? They're going roughly the same speed. The node and consistent speed go hand in hand, and this has been proven quite a few times.
 
#25
Look, I'm not trying to sell you OCW, but you're not exactly correct as I said above. I don't have enough time right now to dredge up all of the tired discussions surrounding it, but there most certainly is more to OCW than just flat spots in the speed node. I do not argue that the chronograph method works, but they are not one and the same nor are they equal to one another. They are simply different methods to reach the same goal.
 
#26
MachoKing said:
and this has been proven quite a few times.
Click to expand...

lash said:
Look, I'm not trying to sell you OCW, but you're not exactly correct as I said above.
Click to expand...

Hell, I need something to do at work today so I'll argue that the chrono only method doesnt work. I tried it after reading about it/the 6.5 guys article and ended up with a load in the scatter node. SDs were amazing but it wouldnt group less than 1.5" when I put it on paper. For that reason I quit trying to save a trip to the range and instead just let the paper tell me what it likes.

Admittedly that is only one experiment but it was enough to put me off of it. Much like culpepper my loads are all right around an sd of 10 when they are done with. So not 3 or 4 like we all strive for but they are the best shooting and I can see that on paper, and thats a fact.
 
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#28
You can always tighten up a group with seating depth. I do not believe that you can have low ES and SD and be in a scatter node. It doesn't make sense, from an engineering standpoint.
 
#29
One thing I hate is a rifle that requires tinkering with seating depth. Case in point, I have some Nexus factory ammo with 136 OTM. COAL is <2.8". Shoots .25 MOA at @100 yards in a basic R700. Says right on the box H4350, CCI BR2, 2800 FPS. Inside is 41.6 grains. Now, how did they figure this one out so that everybody is happy?
 
#32
Not these guys. This ammo is purpose built. This goes back to my original question. .25 moa @100 yards is .25 moa at any other distance. The only thing that is going to change that bullet POI is the shooter and the weather.
 
#33
Culpeper said:
Not these guys. This ammo is purpose built. This goes back to my original question. .25 moa @100 yards is .25 moa at any other distance. The only thing that is going to change that bullet POI is the shooter and the weather.
Click to expand...

You're not getting the fact that at distances closer than 100 yards, the smaller LINEAR differences in POI may be too difficult to notice or discern.

.25 moa @ 100 yards is .25 moa at any distance, but .25 moa covers a different linear distance at 50 yards than it does at 100. Half as much, in fact.

 
#34
No I get that fact. And Lash explained it is easier to read a group shot at 100 yards than 50 when it is posted on here for help. But we have phones now with nice cameras and software that can accurately measure a group at any given distance. This isn't a help me Mr. Wizard moment, lol.
 
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#35
Culpeper said:
But we have phones now with nice cameras and software that can accurately measure a group at any given distance.
Click to expand...

Measuring group size is not how OCW results are interpreted.

You're all over the place with this. I suggest you go read Dan Newberry's explanation of the method as many times as necessary until you understand it. Because it's pretty clear to me that you don't.
 
#36
I'm not all over the place. All I did was start this topic. Everybody is all over the place. Maybe I should have stated analyze a group.
 
#37
A tight group at 100 with a high SD and ES will have less stability down range and will not continue to be 0.25 MOA, unless it's made from laser beams. I've developed loads that were 1/2 MOA at 100 yards but 2 MOA at 300. In my research it shows that a low SD and ES are a good measure of bullet stability.
 
#38
MachoKing said:
A tight group at 100 with a high SD and ES will have less stability down range and will not continue to be 0.25 MOA, unless it's made from laser beams. I've developed loads that were 1/2 MOA at 100 yards but 2 MOA at 300. In my research it shows that a low SD and ES are a good measure of bullet stability.
Click to expand...

You have research results? Care to share it?
 
#40
lash said:
You have research results? Care to share it?
Click to expand...

Not scientific research, like I'm not wearing a lab coat, but I am a stay at home dad and I totally nerd out on all of this reloading stuff and I spend a LOT of time on different reloading forums. Out of all of the different things people argue about, the one thing that seems to be a consensus is that loads capable of long range accuracy have low ES and SD. From the thousands of posts I have poured through, most long range shooters would choose a load that shoots 1/2" with a single digit ES and SD than a load that shoots 1/4" with double digit ES and SD. Now, is it likely that you will find a load that shoots 1/4" with a high ES and SD? Probably not.
 
#41
MachoKing said:
A tight group at 100 with a high SD and ES will have less stability down range and will not continue to be 0.25 MOA, unless it's made from laser beams. I've developed loads that were 1/2 MOA at 100 yards but 2 MOA at 300. In my research it shows that a low SD and ES are a good measure of bullet stability.
Click to expand...

Bullet stability comes from twist rate, not ES/SD. If you had a load that was truly 1/2 MOA at 100 yards (not just some fluke group) in order for it to shoot 2 MOA at 300 yards because of high SD/ES it would need to have an ES of 250 fps. Other factors likely at work there... shooter, environmental conditions, load wasn't truly 1/2 MOA to begin with, etc.


Big picture perspective on all this load development stuff. There are only two things that matter...

1) Does my load shoot well at distance? (ie small groups, tight waterline)
2) How forgiving is my load? (ie what happens if powder charge is off a tiny bit, if temp increases, if barrel/brass conditions aren't exactly the same)

All the methods listed above like OCW, velocity ladder, measuring ES/SD are predictive tools that are attempting to tell you what *might* happen down range. The tools don't trump the actual down range results. The tools aren't infallible, and the tools don't always agree with each other perfectly.

So when you are gathering data during load development if you can't just jump right to 1000 yard groups on paper on a calm morning, try to gather as much data as possible to make an informed prediction on whether your load is likely to shoot well at distance. Don't get hung up on one thing, but try to find a load that has all the key factors. Does it group small, does it have good ES/SD, is it forgiving for powder charge for POI location, group size, and velocity change, is seating depth forgiving as the throat moves?

Get hung up on one method as the "right" one and you're missing good information.
 
#42
Sheldon N said:
Bullet stability comes from twist rate, not ES/SD. If you had a load that was truly 1/2 MOA at 100 yards (not just some fluke group) in order for it to shoot 2 MOA at 300 yards because of high SD/ES it would need to have an ES of 250 fps. Other factors likely at work there... shooter, environmental conditions, load wasn't truly 1/2 MOA to begin with, etc.


Big picture perspective on all this load development stuff. There are only two things that matter...

1) Does my load shoot well at distance? (ie small groups, tight waterline)
2) How forgiving is my load? (ie what happens if powder charge is off a tiny bit, if temp increases, if barrel/brass conditions aren't exactly the same)

All the methods listed above like OCW, velocity ladder, measuring ES/SD are predictive tools that are attempting to tell you what *might* happen down range. The tools don't trump the actual down range results. The tools aren't infallible, and the tools don't always agree with each other perfectly.

So when you are gathering data during load development if you can't just jump right to 1000 yard groups on paper on a calm morning, try to gather as much data as possible to make an informed prediction on whether your load is likely to shoot well at distance. Don't get hung up on one thing, but try to find a load that has all the key factors. Does it group small, does it have good ES/SD, is it forgiving for powder charge for POI location, group size, and velocity change, is seating depth forgiving as the throat moves?

Get hung up on one method as the "right" one and you're missing good information.
Click to expand...

Winner!
 
#43
Well I'm out here with a 260 and a 6.5x284 and each new load group is like SD 6-9 ES in the teens and with the exception of a few nice groups the rest look like shit. So, much for magnetospeed with no target. :)
 
#44
MachoKing said:
Even Newberrys method tells you not to look for the tightest group, as you can tighten a group with seating depth.
Click to expand...

It also says to not go just on chrono results so...pot meet kettle.

308pirate said:
Measuring group size is not how OCW results are interpreted.
You're all over the place with this. I suggest you go read Dan Newberry's explanation of the method as many times as necessary until you understand it. Because it's pretty clear to me that you don't.
Click to expand...

The apps can also tell you how far the calculated center is from the aim point etc which is what we are looking for, not just its diameter. SO they can be very helpful if someone takes the time to do all that. I, like you, just let me eye do the telling though.
 
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#45
MachoKing said:
Not scientific research, like I'm not wearing a lab coat, but I am a stay at home dad and I totally nerd out on all of this reloading stuff and I spend a LOT of time on different reloading forums. Out of all of the different things people argue about, the one thing that seems to be a consensus is that loads capable of long range accuracy have low ES and SD. From the thousands of posts I have poured through, most long range shooters would choose a load that shoots 1/2" with a single digit ES and SD than a load that shoots 1/4" with double digit ES and SD. Now, is it likely that you will find a load that shoots 1/4" with a high ES and SD? Probably not.
Click to expand...

Might want to go shoot instead.......
 
#46
Hah, I do shoot, but I am addicted to researching everything I do. I'm not saying that ES and SD are the only thing to look at when developing a load, but 99% of the time, a good load will have a low ES/SD. I personally like the OCW method but I can't discount the chronograph method either. If you could afford a labradar, you could basically run both tests at the same time and get the best of both worlds. I would love to see more empirical research on a lot of this stuff but I'm sure it would cost a lot of money and have very little return value, monetarily.
 
#47
Culpeper said:
Well I'm out here with a 260 and a 6.5x284 and each new load group is like SD 6-9 ES in the teens and with the exception of a few nice groups the rest look like shit. So, much for magnetospeed with no target. :)
Click to expand...

It’s all about barrel time; actually, barrel time with tight SD is what you’re looking for
 
#49
mijp5 said:
It’s all about barrel time; actually, barrel time with tight SD is what you’re looking for
Click to expand...

The QB barrel time matched up with the 29.5" 260 average velocity spot on. For the 26" 6.5x284 it was not a good indicator (off by .054 milliseconds :) )

BTW, I was shooting at 100 yards, lol.

260, 41.7 AA4350, 136 Scenar-L, CCI BR2, 2795 MV, SD=5, ES=13

6.5x284, 51.0 H4831sc, 142 SMK, CCI BR2, 2788 MV, SD=5, ES=14
 
Last edited by a moderator:
#50
Culpeper said:
The QB barrel time matched up with the 29.5" 260 average velocity spot on. For the 26" 6.5x284 it was not a good indicator (off by .054 milliseconds :) )

BTW, I was shooting at 100 yards, lol.

260, 41.7 AA4350, 136 Scenar-L, CCI BR2, 2795 MV, SD=5, ES=13

6.5x284, 51.0 H4831sc, 142 SMK, CCI BR2, 2788 MV, SD=5, ES=14
Click to expand...

I wasn’t talking more in terms of conceptually. I’m not aware of being able to absolutely calculate the time without error.

Let me rephrase my original statement, which has been stated above by some other guys: tight SD doesn’t mean much if it is between nodes
 
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