Developing an OCW "Optimal Charge Weight" load

[jankovig]

First of all, I'm a total virgin when it comes to reloading. I haven't loaded a single round...yet, but I have been doing a lot of reading and in the process came across the concept of developing an OCW load.
Here's the link to the site
http://optimalchargeweight.embarqspace.com/#. Just wanted to see what more experienced loaders think of it.

 

[ykkid]

If you haven't started hand loading at all yet, it would seem to me this is a concept you need not concern yourself with for a long time. It would seem the idea is to develop one load that shoots accurately for several different firearms. If you personally have several firearms in one caliber, and you do not want to maximize the accuracy in each, nor keep most accurate loads for each seperate, then his concept of OCW would fill the bill.

But, before that, you have the joys of learning to create a safe load, then a most accurate load, and, inevitably you will want to skirt disaster with "hottest" load. (We can all hope here that you survive this phase with no burst receivers, ruptured cases, tattooed cheeks or blinded master eyes, before you learn that even in women, "hottest" is seldom best.)

Far more useful for most of us is to develop loads with a variety of bullets with close, if not exact, points of impact. A premium hunting bullet, perhaps in a couple of different weights, mayhaps a match bullet or two, some nice cheap plinking bullets to practice marksmanship, and a nice reduced load to practice riflery - the administration of the firearm - and of course, in today's insane world, some leadfree selections to frustrate the eco-terrorists.

Even if you don't get many of these striking close to the same point of aim, the development of all these loads, in just one firearm will keep you working OT to pay for all the components, and shunning friends and loved ones to get time to assemble and test all these loads.

OCW? Why bother?

 

[TwoTone]

...It would seem the idea is to develop one load that shoots accurately for several different firearms...

I didn't get that at all from that website. It's about tuning a load to a specific rifle.

...OCW? Why bother?

I think its a great system for developing a good load. I'd say why not bother? You can waste a lot of time and components if you don't go about it in a systematic way.

That's not to say you can't develop a good load by other methods, but this way strikes me as a good way to find a forgiving load. I've used it and it works very well.

Why not start off on the right foot instead of floundering around?

 

[chemo]

I've bothered with the OCW, what I could never really figure out is this:

You will now look for the three groups which come the closest to hitting the same POI (point of impact) on the targets. The trend of the groups should be obvious, normally going from low and favoring one side, to high and favoring the other side. But along the progression, there should be a string of at least three groups that all hit the target in the same relative point.

After you have carefully measured group sizes and distances and directions from the bullseye, you will know which three groups come the closest to hitting the target in the same POI. You now choose the powder charge which represents the center of this string. For example, if 34.7, 35.0, and 35.3 grains all grouped about 1.5 inches high, and about 3/4 of an inch right of the bullseye, you would choose the 35.0 grain charge as your OCW (optimal charge weight). This charge will allow 34.7 and 35.3 grain charges to group right with it. This will be a very "pressure tolerant" or "resilient" load.

So is he actually saying the 35.0gr load is the OCW but you should use either 34.7 or 35.3gr??

Another thing that really threw me off is the "scatter group". From my understanding, he is basicly saying the group that opens up (ie worst grouping) is damn near, ±1-2%, the OCW. On the other hand, he mentioned in previous quote that this very ±1-2% around the OCW is where the load should "group right with it"

quote about the scatter group:

I show all of the targets above because 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.

One day when I figure what he really means, I might do this method entirely. For now I just load acording to his instructions, shoot the round robin, then triangulate for best group... No scatter group, no OCW per se

 

[TwoTone]

So is he actually saying the 35.0gr load is the OCW but you should use either 34.7 or 35.3gr??

I think he means that if you have 35.0 for an OCW it gives you some wiggle room if your powder measure happens to throw a 34.7 or a 35.3 charge instead of a 35.0 charge, you'll still be in the group.

Can't comment on the 'Scatter Group', haven't noticed it.

 

[rgv]

the theory has merit

where it falls apart in the real world, is that it depends on an accurate rifle, and a shooter who is capable of shooting flawless three shot groups.

Anyone who has shot much, knows how difficult it is to rely upon a single three shot group, which in effect you are doing with his description of OCW load development.

So given an accurate rifle, and a good shooter, why bother with time consuming graphical analysis? Simple development with an appropriate pwder and the bullet of choice will get you where you need to be.

 

[looch]

I've bothered with the OCW, what I could never really figure out is this:



So is he actually saying the 35.0gr load is the OCW but you should use either 34.7 or 35.3gr??

Another thing that really threw me off is the "scatter group". From my understanding, he is basicly saying the group that opens up (ie worst grouping) is damn near, ±1-2%, the OCW. On the other hand, he mentioned in previous quote that this very ±1-2% around the OCW is where the load should "group right with it"

quote about the scatter group:



One day when I figure what he really means, I might do this method entirely. For now I just load acording to his instructions, shoot the round robin, then triangulate for best group... No scatter group, no OCW per se

After the scatter group occurs, you are "in the OCW zone" - meaning that a 1-2% powder increase will have you in the low end of the range of OCW loads, not the optimal, mid-point. So, in the example, he would have seen a scatter group at 34.4, then 34.7, 35.0, and 35.3 would be the string of groups with the POI in the same location.

 

[looch]

What I had a hard time with is accepting that the tightest group is not necessarily the best load. Since you are doing round robin, anomalies that manifest over time spread themselves across the groups. It's the average POI that's important and that it stays consistent for that string of 3 consecutive groups. For instance, I got a little impatient and my barrel started to heat up. By my 3rd round robin, my POI changed and my groups opened up. It didn't matter - the average POI of those 3 consecutive groups remained close.

 

[kombayotch]

Anyone who has shot much, knows how difficult it is to rely upon a single three shot group, which in effect you are doing with his description of OCW load development.

So given an accurate rifle, and a good shooter, why bother with time consuming graphical analysis? Simple development with an appropriate pwder and the bullet of choice will get you where you need to be.

The problem with the "simple" load development process is that people focus on group size and neglect the barrel harmonics. It is apparent in your three shot group statement that you're talking about group size. The reason you look at location in the OCW is because consistent group center location over a charge range tells you that the muzzle is in a relatively calm state. If you have have a good shooter and an accurate rifle, the test is very repeatable as far as group center location goes. See my example here: http://www.canadiangunnutz.com/forum/showthread.php?t=289047&highlight=ocw&page=3 It was repeatable even with a different brand of brass.

A small change in charge weight has the same effect as a change in powder burn rate due to a change in temperature and/or pressure. If you've actually run a number of OCW tests, one thing that you will notice is that often you will get two nice small groups, but they will be at significantly different points of impact. And it will happen again and again if you repeat the test. That means the barrel is not calm, its "whipping" and if you use one of those charges, you are much more likely to get a change in zero out in the field under different conditions.

People who are only concerned with group size and have slighter shots may not care about this, but those interested in making precise first round hits are. Choosing a temperature stable powder makes the load that must more robust and resistant to changes in zero.

 

[rgv]

The problem with the "simple" load development process is that people focus on group size and neglect the barrel harmonics. It is apparent in your three shot group statement that you're talking about group size. The reason you look at location in the OCW is because consistent group center location over a charge range tells you that the muzzle is in a relatively calm state. If you have have a good shooter and an accurate rifle, the test is very repeatable as far as group center location goes. See my example here: http://www.canadiangunnutz.com/forum/showthread.php?t=289047&highlight=ocw&page=3 It was repeatable even with a different brand of brass.

A small change in charge weight has the same effect as a change in powder burn rate due to a change in temperature and/or pressure. If you've actually run a number of OCW tests, one thing that you will notice is that often you will get two nice small groups, but they will be at significantly different points of impact. And it will happen again and again if you repeat the test. That means the barrel is not calm, its "whipping" and if you use one of those charges, you are much more likely to get a change in zero out in the field under different conditions.

People who are only concerned with group size and have slighter shots may not care about this, but those interested in making precise first round hits are. Choosing a temperature stable powder makes the load that must more robust and resistant to changes in zero.

your description in the other thread is better than dan newberrys.

the quote from your post that I emboldened has convinced me to try it, as much as I abhor any sort of graphical analysis, in fact I almost gave myself an anxiety attack when I found a pad of Wulff Nets in my filing cabinet the other day.

 

[kombayotch]

Yeah, his example isn't that great...

 

[chemo]

After the scatter group occurs, you are "in the OCW zone" - meaning that a 1-2% powder increase will have you in the low end of the range of OCW loads, not the optimal, mid-point. So, in the example, he would have seen a scatter group at 34.4, then 34.7, 35.0, and 35.3 would be the string of groups with the POI in the same location.

makes alot of sense thanks !

 

[jankovig]

My understanding of the whole OCW concept is to develop a load that's going to shoot well in different rifles of the same caliber.
I initially plan on reloading for a 7mm Rem. Mag., then 30-06 and maybe 303 British.
I guess I'm just looking for a more systematic approach to reloading (be it OCW or anything else), rather then the shotgun approach.

 

[kombayotch]

It is more systematic. The loads that I developped using this method have performed well in several barrels now, with only minor tweeking.

I've also found that many loads that are known to perform in different rifles fall on the OCW. Other methods can get you to the OCW without you realizing that you're on the OCW (or even having knowledge of it). However, DN's method gets you there relatively quickly. The only way I have found thats faster is using my Pressure Trace system and relying on the OBT marks.

 

[Ruger No.1]

I started using a modified version of DN's OCW last year. Instead of shooting separate load targets and then plotting group centers, I shoot all my groups on one target "ladder style". You very quickly see the sweet spot for a specific barrel. Like Kombayotch, I have found it is the one of the quickest ways to focus in on one load for fine tuning (ie. changing seating depth, etc.).

As has been pointed out, this method is only effective if the shooter and the rifle are capable of consistent, reasonably accurate shooting (Newberry suggests MOA) .