I completed this test about a month ago, but I though I'd post the results here now. The basic idea here is the there is an "optimal charge weight" of powder for a given load recipe, wherein a slight pressure increase or decrease won't affect the velocity enough to change POI considerably. Such a load can tolerate slight powder variations, as well as temperature changes and minor component lot variations without going to pieces like many of our favorite loads do.

If you've ever been troubled by lot variations, or if your load just seems to work well one day and not so well the next, you may want to redevelop with an eye toward the OCW concept. I base this loading concept loosely on Creighton Audette's method, but it is easier to execute, and yields more definitive results.

Following is a synopsis of a test to find the OCW of IMR 4895 in the .308 Winchester when the 168 grain Sierra Matchking is being used.

********************************************

I finished the first phase of testing IMR 4895 with the 168 SMK (.308 win) today. The rifle was my Savage 10FP, 24" barrel. Scope used was my Weaver Grand Slam, 6.5 to 20 power.
I began with virgin Winchester brass, Federal GM primers, and the above mentioned bullets and powder.

My Speer book lists 44 grains of IMR 4895 as being the max charge to be used with the Speer 168 grain match bullet. I feel that is also a safe limit when using the 168 grain Sierra Matchking.

I decided to begin with 43.0 grains of IMR 4895, since I expect the OCW to be found near the maximum charge, and to move up in .3 grain increments.

Overall length used was 2.870". I fired three shots each of the following powder charges. The POI's mentioned reflect the fact that my scope was off about 2 MOA to the left. (I had just installed a different set of Burris Signature offsets, and hadn't corrected the windage yet).

The POI figures reflect the triangulated average of the three shots.

43.0 grain charge...... 2.16 inches left of POA,
.45 inches high
group size .20"

43.3 grain charge...... 2.45 inches left of POA,
.85 inches high
group size .27"

43.6 grain charge...... 2.50 inches left of POA,
.90 inches high
group size .80" (ooops!)

43.9 grain charge...... 2.75 inches left of POA,
1.0 inches high
group size .30"

44.2 grain charge...... 2.56 inches left of POA,
1.5 inches high
group size .90", in a
diagonal string

44.5 grain charge...... 2.70 inches left of POA,
1.4 inches high
group size .33"

Yeah, I know, I went a half grain over max with that last load, but saw no pressure signs...

I cleaned the bore after the first two groups, and again after group four. One fouler shot was fired after cleaning.

Conclusions:

My tightest group was the first one fired, using the 43.0 grain charge. It measured just under 1/4 MOA. However, by moving up only .3 grains, to the 43.3 grain charge, my POI jumped up in elevation by about 3/8 MOA. That's not awful, but at extended range, the 3/8 MOA move could be significant. The group also made a noticeable move to the left.

I think I pulled the 43.6 grain group apart. I'm not *sure* of that, but it would seem, from the sizes of the other groups in the test that a "loose nut on the trigger" must have been the cause. Heat mirage was beginning to play around with me by this time.

I note that the 43.3, the 43.6, and the 43.9 grain charges all were within 1/3 MOA (measured either vertically or horizontally). I am tentatively calling 43.6 grains the OCW, but I will have to prove that out.

My next range trip will consist of shooting three shot groups with one shot each of the three charges listed above, and measuring the group sizes. If they come in at half MOA or close to it, I'll be pleased. I expect that they will, based on the results posted above.

Another point worth mentioning is that these loads all shot tight using Winchester virgin brass.

The + and - .3 grain test would be worth trying on your own match loads. This would give you an idea of where your group size will be if and when component lot variations, or outside temperature cause pressure changes which mimic the .3 grain powder variances.

Dan Newberry
green 788

Don't feel bad for the lack of replies. I typed at least one answer to this thread and finally I got reregistered.

On the topic I try to be scientific also so I appreciate your efforts.

What are you going to do next?

Perhaps repeating the test as before?

Looks like an excellent endeavor to do.

A couple of things you might consider. The group excursions may not be your fault but a change in the barrel harmonics causing the group change. This is still very good information and what you are looking for in your "OCW" thesis. Retest these loads again to see if it repeats. That is the first rule in scientific testing, "IT MUST BE REPEATABLE BY YOUR PEERS".

If you haven't already did it, you should number your cases and keep them segregated so you are testing OCW not case variation. I'm not trying to get all uppity here, just a few observations. I don't know you or your background. You may have already taken all this into account. I noticed how groups change in relation to powder charge, primers, bullets, cases quite a long time ago but figured it was me doing something wrong. Wasn't until I figured out that the targets were telling me a story and I should listen that I finally put two and two together. Still doesn't come out 4 with me always, though. One other observation is your groups jumped after cleaning. You said you cleaned after group 2 and 4 and group 3 and 5 were both large. You might fire a 3 round group into another data target to see if this is the case after cleaning. I've noticed this happening to my better shooting rifles along with increasing velocity on my chrono until the 4th or 5th shot after cleaning.

I'm looking forward to more data. I NEED DATA, MORE DATA....uh...sorry...lost it again.

Makatak

Thanks for the interest, guys... I have in fact tested the 43.6 grain charge of IMR 4895 (168 SMK, .308 win) at 300 yards, and again at 600. This was all done last month. I dragged this thread over here from Snipershide.com after it appeared that our posts were gone. I thought I'd help reestablish some conversation, as well as get the opinions of you guys here at Accurate Reloading. There are a lot more members here...

Following is my post regarding the 300 yard test of the suspected OCW charge in question:

I shot the 168 SMK/IMR 4895 OCW load today at 300 yards. I was shooting with a crosswind, trying to catch the lulls. Oh yeah, it was raining too.
But things went well, considering.

I considered the first group the control group. It was a five shot group using the mean charge (developed via the method described on the other OCW threads). The mean charge was 43.6 grains of the IMR 4895. Cases were the same Winchester cases used at the beginning of the test, now once fired. Primers were the Federal 210 Gold Medals.
OAL was 2.870", again, the same specs as used in the test.

The five shot control group came in exactly at MOA, 3 inches. Vertically, the group measured a little under 2 inches, however. I think the wind opened up the group laterally. I had dialed in 2 MOA of windage to get the shots on the bull.

Then I went to the staggered loads, to test resilience. I fired one three shot group, and was having difficulty spoting the holes on the wet target. The first group consisted of one each of 43.3 (low charge), 43.6 (mean), and 43.9 (high charge). These three shots--I kid not--were all within an inch and a half of each other--half MOA. I fired another group which again consisted of one low, one mean, and one high. I couldn't spot the shot made with the mean charge, so I fired a second shot into that group, using another cartridge loaded with the mean charge. By this time, the wind had subsided and the rain had begun only to drizzle.

The fourth shot in that second test group actually touched the other mean charged shot. I couldn't see the first one because it was on the black border of the square I was aiming at. This four shot group, again spread somewhat laterally, measured 2 1/2 inches. Vertically, it was under 2 inches.

My conclusion is that the OCW charge of IMR 4895 for the 168 SMK in the .308 win. chambering is 43.6 grains. The groups shot with the high/low variances were actually *tighter* than the control group. I'm sure this wouldn't be the case all the time, but I'm convinced this load will be a resilient load.

The final phase of this test will be done at 600 yards. I'm hoping to hold MOA at that range as well. The 43.6 grain load shoots 1/4 MOA at 100 yards without much trouble, so if it will shoot 1/2 MOA at 600 yards, the high and low loads shouldn't take the group beyond MOA, or 6 inches.

I feel confident enough at this point to recommend the load to any shooters looking for a resilient 168 grain match load for the .308 win. If the 43.6 grain charge doesn't group to your expectations, you might try a primer swap, or simply tune the OAL instead of altering the powder charge.

*************************************

The above test was done in mid April if memory serves. I did use once fired brass, as mentioned, but I did that because I wanted to be sure the 43.6 grain charge of IMR 4895 would perform as well with once fired brass as it did with virgin brass. That's one of the good things about an optimal load--you don't have to fireform cases to get good performance. The pressure changes (which are a result of the virgin brass versus fireformed brass) are hopefully accomodated by the optimal charge. We have virtually identical points of impact at 300 yards with 43.3 and 43.9 grains of powder. I'm certain I'm not overbore (powder burning after the bullet exits the muzzle) because the 44.3 grain charge in initial testing moved the POI notably.
So, the pressure variations brought on by component lot variances, weather, and virgin brass will be minimized or eliminated by using the optimal 43.6 grain charge of powder.

I do have the 600 yard data as well, and I'll bring that over later on.

One other shooter at snipershide tested this method using the .223 Rem and H335, and it seemed to work well for him. In smaller cases like the .223, we were using .2 grain variances instead of .3 grain ones. In large magnum cases, it might be beneficial to go with a .4 grain variance.

Also, if a rifle and prospective load doesn't posess MOA accuracy capability, the whole test would probably be an excercise in futility. Heavy barreled small caliber rifles may need to have initial test performed at 200 yards, rather than at 100.

I failed to fully explain the reasoning behind this load development method before launching into this whole thing. I do think I posted the thesis here a while back, I'll have to check, and perhaps bring it current if it's there...

Anyway, I would like comments, positive and negative--especially constructive criticism, which may help this evolve into something useful for a lot of folks.

Dan Newberry
green 788

Dan Newberry, I am somewhat confused by what you are proposing. I am familiar with Creighton Audette�s method and yours is similar. Both his and yours assume that a suitable seating depth has already been found and you are just tweaking the powder charge to come up with a charge in the middle that is insensitive (a bit less or more powder is not going to affect group size appreciably). So I understand the concept but again it requires that a seating depth that the gun likes has already been found. That is my problem. I have not found a good seating depth other than one that puts cartridges longer than my magazine box will allow. Then you introduce Gerard Schultz�s method which is totally different. He suggests seating the cartridge as long as the box will allow (unless the bullet is touching the lands before that point in which case the bullet would be seated to touch the lands) and then picking a suitable powder and working up to a maximum yet safe velocity. Then if that load is not giving acceptible accuracy start seating the bullet deeper and deeper until it is shooting tight groups. I am thinking that I will have to start with the Schultz method initially. So if I understand his method correctly I would take whichever bullet I wanted to use, load it to about 3.580� and select an appropriate powder and then work up in charge weight until I am at max safe velocity. Then start seating deeper until the load was shooting good. If that is correct, then the final question is what increment in seating depth should be used? If I go in 0.005� increments it could take a lot of shots before getting there but on the other hand if I go in 0.050� increments I could well miss it. If I use this method then once it is shooting good maybe I can alter the powder charge a bit to see if I can come up with a charge weight that is in the middle of an insensitive range of charge weights. Am I on the right track?

Thanks for your help, Rufous.

I received an email a while back regarding my OCW load development method. It was from Gerard Schultz of GS Custom bullets... I hope he won't mind me referring to it here:
Hello Dan,
Your method of load development is right on the money. I have designed 140 new bullets and developed optimal loads with them in even more calibres over the last 9 years and this method is the only way to go. Tuning a group by varying the load is a waste of time and components. If the col for a rifle is optimised, speed variations are of lesser importance. See the page below on our website where we recommend a very similar method.
http://gunlinks.zibycom.com/members/002245268/Site2/hvloadguide.html

Regards
Gerard

Anyway, what I'm getting at is that you're right to be looking at the OAL (distance to the lands) as a *fine tuning* of your load. I believe, like Gerard does, that adjusting powder charges in search of the best load is not the best approach.
You're probably better off not starting with a preconceived notion as to what distance from the lands your rifle likes. The truth is, it probably likes a *lot* of different distances from the lands. The OAL should be the last adjustment made. Often times we decide via one device or another that our rifle really likes .015" off the lands, and then tune powder charges to make that distance work. You can just as easily back off to .025" and adjust the charge and accomplish the same thing.
Look at it like building an engine. Powder selection and charge weight is equivalent to piston (compression ratio) selection. The OAL adjustment is like adjusting the *timing* of the completed engine. Yes, you can select a particular advance in timing, and alter compression ratio, etc, to make the engine perform with that particular timing advance, but you'd be working backwards.
There is an optimal amount of powder in a given load recipe that burns most evenly and consistently. Find that charge weight by the OCW testing method or any other such method that might work for you, then *tune* your accuracy with OAL adjustments as a final step.
Best of luck in your load development, Dan

I believe that OAL should be changed last, and that there are various OAL's which will work well in a given rifle--this will depend not on the bullet itself, but on the powder charge you're using. I believe that tuning the OAL is what brings you to the sweet spot in your barrel's harmonic cycle, but you don't want to tune the OAL until you have an optimal powder charge.

Look at all of the excellent factory ammunition (I'm talking about sub MOA stuff like the Super-X Winchester Power Points in the .270, 30-06, and even in the picky .243's). These OAL's are obviously the same, but they perform very respectably in a variety of rifles. Winchester has found optimal charge weights of their powder, and these charges burn so consistently, the load perform well in spite of the fact that OAL's are pre-set...

What I suggest is that you find the powder charge where you're up to a good velocity, and then find that zone of .6 grains or so which yields the same POI for any cartridge loaded with a charge weight in that .6 grain wide zone. Remember, I fired shots varying from 43.3 grains to 43.9 grains of powder, and they hit the target in the same spot at 300 yards (they did as well at 600 too, I'll mention more later on that)...

So you don't begin with a known optimal OAL--there won't be any way to know where the distance to lands will need to be until you find the OCW zone.

Do this: Take your current load, and load up some about .4 grains under (you're shooting a magnum I presume), and .4 grains over your usual charge. Shoot three shot groups using a low, normal, and high charge load and see how they compare with a three shot group of three normally charged shots. If the low, normal, high group isn't pretty near as good as the control group, then you don't have an optimal powder charge.

I should probably bring to the top the thread where I explain the whole method in detail. That would probably help, and I apologize for not having done so already...

In a nutshell, you're looking for a load that can take a variation in the powder charge of somewhere around 1.5 to 2% and still perform, hitting basically the same POI, preferably holding MOA. When you have that powder charge, *then* you tune for group by adjusting OAL...

Dan Newberry
green 788

Can anyone point me to Creighton Audette and Gerard Schultz. I would like to get some more information on their methods. I've been using powder charge, seating depth, primer and bullet changes for 40 some years and didn't know there was a "method" to doing it.

I always used three begining points; 1. Touching the lands and 2. Midrange on the powder amount and 3. A powder that filled the case at least 85% and gave the highest velocity with the lowest pressure. It has always worked, but I'm always looking for new and better ways to reduce the time and expense of getting a new rifle to shoot straight. If all else failed a primer change sometimes made the difference. Usually took less than 100 rounds to get a shooter. I have ran into a few rifles that never cooperated and they ended up on the auction block.

I've been studying the load data on this site trying to discern any repeating patterns or any patterns at all but just when I think I have one it, falls out. It is very appearant that powder amount changes have a powerful influence on the group size. A .2 or .3 change can cause a group to go from 1.5" to .3" and back again.

I thought I had a lock on it with one of the smaller calibers where a .2 change was adding about 100fps and going from 1" to .2 to 1.2" to .3 to 1" to .4" and so forth. It held through several powder and bullet changes, then toward the top end of the powder things got lost. Maybe that was where the OCW was exceeded. It looked like the seating depth was established and left alone and the charge was the only thing being changed. I'm doing an analysis of sorts with this data, but not getting too far with it, too many other things getting in the way.

What I would like to see is some tests done that would establish a seating starting point for each caliber that is more than just a guess. I'm not sure if this is possible and the "theory of harmonics" would suggest this is not the case, with a few exceptions.

Ah, but if that were the case and everything was known, this sport would get real boring, real fast.

"A .2 or .3 change can cause a group to go from 1.5" to .3" and back again."

That's exactly true, as many of us have found out...

The advantage to optimizing the powder charge is that .2 to .3 or perhaps even .4 grains above or below the normal (mean) charge won't drastically bother your groups.

Why would you want such a load? Well, such an optimized load can tolerate changes in brass lots, powder lots, etc., much more easily than non-optimized loads can. If you load a batch and your scale is off a couple of tenths, you'll probably still be fine...

Have you ever thought you had "the load" only to find out on the next trip to the range that it was all over the paper?

What may have happened is that weather/atmospheric conditions changed slightly, and caused a pressure *drop* or *increase*, and your load is now acting like it has .3 grains less, or .3 grains more powder in it. How many of us use loads that misbehave when it gets really hot outside? An OCW load will buy you a few degrees of mercury...

Many of us have come upon load recipes that just seem to perform no matter what. We credit the rifle, but the load recipe may deserve the credit.

And many of us have traded off scopes that "wouldn't hold zero." Every trip to the field or range seemed to yield a POI change. It may well not have been the scope, but rather a precarious load recipe that was the culprit... Believe me, I've done it.

Again, my basic rule of thumb to test the resilience of any load is to load about 1% below and 1% above the normal charge, and fire a three shot group, consisting of the high, low, and normally charged shots. Compare the size to a three shot group with three normally charged shots, and you'll have a much better idea of how that load is really going to perform when the weather or component lot variations cause pressure changes...

Dan Newberry
green 788