OCW Fine Tuning

[SABuzzard]

Ran my first OCW test and found what looks like a clear winner... one group whose average POI shifted very little from the group before and after it. I was working up in .5 grain increments and my "sweet spot" settled in at 45 grains Varget (308 win 175 SMK).

Should I continue with another round of the OCW using .2 grain increments around the 45 grain mark or is this as close as it needs to be and start working on seating depth or other variables?

 

[Tripwire]

Re: OCW Fine Tuning

Personally I like to find the exact top and bottom of a node. In anything short of a large magnum chambering this means retesting the node in at LEAST .2 grain increments though I've found .1 grain increments to be more definative, and yes, I want to see the exact end of the low scatter node and the exact beginning of the high scatter node. Pretty simple from there to pick the exact center of the accuracy node.

From there, IF the groups aren't quite good enough then I'll adjust the timing of the bullet exit with VERY small changes in seating depth.........

 

[Bob 964]

Re: OCW Fine Tuning

If you have a sweet spot that spans from 44.5 to 45.5, and there is very little shift in the average POI from 1 load to the next, then I'm not sure what is to be gained by doing another OCW test using 0.2 gr. increments. Certainly it won't hurt, but it were me, I'd be comfortable with an OCW of 45.0, and I would load 5-round groups at 45.0 gr. and different seating depths and see how they group.

 

[Tripwire]

Re: OCW Fine Tuning

Squarenut, read this sentence....

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">one group whose average POI shifted very little from the group before and after it.</div></div>

Shifted very little....how about ZERO shift of POI?

That's my goal with OCW and his .5 grain testing is a good roughing in but it takes smaller increments to confirm or deny that load. Maybe he got lucky this one time, but I doubt it.

 

[SABuzzard]

Re: OCW Fine Tuning

Thanks guys

I'm going to try another round working up in .2 increments to see where things settle out.

Let you know what it shows

 

[X-fan]

Re: OCW Fine Tuning

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tripwire</div><div class="ubbcode-body">Personally I like to find the exact top and bottom of a node. In anything short of a large magnum chambering this means retesting the node in at LEAST .2 grain increments though I've found .1 grain increments to be more definative, and yes, I want to see the exact end of the low scatter node and the exact beginning of the high scatter node. Pretty simple from there to pick the exact center of the accuracy node.

From there, IF the groups aren't quite good enough then I'll adjust the timing of the bullet exit with VERY small changes in seating depth......... </div></div>

Money right there.

0.2 grains sounds fine enough, but it gives you no room for error.

We all screw the odd shot or lose one to the wind so I like 0.1grain 3 shot groups.
This gives you a lot of information and the best chance at pattern recognition.

 

[gvanhyning]

Re: OCW Fine Tuning

Just a suggestion SABuzzard ... I start my initial OCW at .2 grains increments up to a max that I have identified. That really narrows the gap and reduces the number of trips to the range. Good luck.

 

[MitchAlsup]

Re: OCW Fine Tuning

The final step in OCW is to make a sweep around the chosen load so you can determine how wide is the window of charge weight. A wide window that all shoots good, is indicative that you have found the OCW and also indicative that you can pretty much use a throw and go loading regimen.

The sweep should be in 0.5% increments, or as fine as your scale can measure accurately and repeatably.

The real OCW is the mid-point of the window that all shoot "peachy keen".

 

[Bob 964]

Re: OCW Fine Tuning

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tripwire</div><div class="ubbcode-body">Squarenut, read this sentence....

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">one group whose average POI shifted very little from the group before and after it.</div></div>

Shifted very little....how about ZERO shift of POI?

That's my goal with OCW and his .5 grain testing is a good roughing in but it takes smaller increments to confirm or deny that load. Maybe he got lucky this one time, but I doubt it. </div></div>

Thanks Trip... you are far more experienced than I. Perhaps I need to raise the bar a bit for my testing.

 

[SABuzzard]

Re: OCW Fine Tuning

Looks like I have some loading to do. I'm going to work it out completely from 44.5-45.5 in .1 grain increments and see what happens.

Thanks for the input. I'll post my results and probably come back with 5 more questions.

 

[Tripwire]

Re: OCW Fine Tuning

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SABuzzard</div><div class="ubbcode-body">Looks like I have some loading to do. I'm going to work it out completely from 44.5-45.5 in .1 grain increments and see what happens.

Thanks for the input. I'll post my results and probably come back with 5 more questions. </div></div>

I know it sounds like a lot of shooting, but this where you need to know exactly what's going on, if that matters to you. If you think your node might only be a grain wide, then it's quite possible you might be cheating yourself. How else will you know unless you put rounds on paper?

People need to understand that bad data is just as valuable as good data. Finding the shit loads below your good load, and the shit loads above your load, are worth their weight in gold because now you know not to go there again. You won't see it unless you shoot it. Only testing 44.5 to 45.5 because you think 45.0 is THE load is a mistake in my book, especially since you are basing this off of an initial .5 grain work up. I ALWAYS test at least 3/4 of a grain above and below the suspected center of the OCW, and have even been known to go a whole grain above and below, and have found nodes much wider than just a grain.

The next OCW test you do for a rifle that's NOT a magnum large capacity case really needs to be done with increments much finer than a half grain. It's just too easy to skip over the valuable data. Again, I know it's a lot of shooting, but you can at least help yourself a little bit by shooting only 3 round groups.....and I do it now with single round or two round groups, just to conserve resources. If you and your rifle are up to it, it can be done that way.

OCW is a refined method of load development that by it's very nature and principle, if applied as Dan Newberry intended it done, elevates the user above most run of the mill reloading methods. It all boils down to timing the exit of the bullet at the precise nanosecond that gives the bullet the best opportunity at a clean uninfluenced exit from the muzzle. Why fool with it if you aren't willing to take it to the level it offers?

Spend some time doing a proper test and the rewards will last a long LONG time...........

 

[X-fan]

Re: OCW Fine Tuning

Well said again Trip.

The 308 can be an extremely precise round and thorough initial load workups provide so much critical data that can be referenced down the road.
Ideally you would record shot velocities, temperature, and any pertinent environmentals.

With regard to shooting smaller groups than 3 shots I think this very much relates to an intimate understanding of your personal marksmanship as well as the capabilities of your rifle. Put another way...If you have a benchrest capable rifle/scope, wind flags, and shoot 0.1's and 0.2's frequently then one shot will likely do. For a long living cartridge (like the 308) I prefer 3-5 just for confirmation of a solid data point (5 shots being a bit excessive).
Then again I don't mind shooting a bit extra and sending lots of lead!

Good luck!

 

[SABuzzard]

Re: OCW Fine Tuning

I'm committed to doing it the right way. Accuracy is the name of the game. It's great to get feedback from those with experience and know you're not spinning your wheels.

 

[vman]

Re: OCW Fine Tuning

SABuzzard no harm in confirming. Take that load out far and you will see any vertical dispersion really start to show up. You may find you need to tweak around with minor powder adjustments, maybe even seating depth... but by all means, confirming what you have at longer distances is a smart thing to do.

 

[Tripwire]

Re: OCW Fine Tuning

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">SABuzzard no harm in confirming. Take that load out far and you will see any vertical dispersion really start to show up. You may find you need to tweak around with minor powder adjustments, maybe even seating depth... but by all means, confirming what you have at longer distances is a smart thing to do. </div></div>

If you have followed the OCW principles to the letter, found your accuracy node in the initial phase, and reduced the groups as much as possible in the second phase, then you have addressed all the issues that accumulate to good accuracy....it will be the best your rifle can do with that set of components.

IF the load then does not perform at distance then there are other things at play that have nothing to do with the OCW....environmental conditions, wrong twist, bad bullet choice, high degree of runout, bad shooter technique, etc.

You simply cannot refine a load any more with powder weight adjustment when you've already found an entire range of powder weights that work and have crossed the line into super fine adjustment with minute seating depth adjustments that adjust barrel timing in much smaller increments than even a tenth of a grain of powder change can produce.

The whole idea behind OCW is finding a RANGE of powder weights that work the same, stepping outside of that range in the name of refining the load changes what you've already accomplished, which was finding THE perfect powder weight to begin with.

If this concept is too hard to grasp then you need to study a bit more on OCW......

 

[deadnbrkn84]

Re: OCW Fine Tuning

Tag

 

[X-fan]

Re: OCW Fine Tuning

I would like to add that if you don't like what the OCW is giving you in accuracy you are likely using the wrong powder...I see this all the time.

The powder that gives the highest velocity may not always be the best powder for producing hair splitting accuracy along with long forgiving accuracy nodes. My two 338 edge rifles are a great example of this.
Using 300 grain bullets with Retumbo and H-1000 I found Retumbo the fastest powder giving me close to 2950fps along with 1/2 MOA accuracy. Without OCW testing most guys would take the 1/2 MOA and go to distance...Then as time went by and weather and temperature changed they would blame the fliers on themselves or the wind.

H-1000 on the other hand produces slightly better accuracy at 2840fp, but seems virtually unaffected by weather or temperature and drives spikes upon command.
In my rifles there is none better.
This all showed up in my OCW tests and (because I wanted more speed) was confirmed by shooting at ELR.

If your load can't produce a tight OCW at 100 yards it will not shoot as forgivingly to conditions as one that does.

Though I have never seen this it is theoretically possible to shoot a good OCW with excessive velocity variation then have that load produce poor vertical grouping at distance. For this reason I shoot my OCW testing over a chronograph while watching for tight extreme variation.
When the H-1000 dropped 4 bugholes into about 1/4" at the same POI as most of the rest of the target I looked at the chronograph....2836, 2836, 2836, 2842...and I knew I had winner!

Hope that helps those trying to wrap their noodle around the OCW thing.

Peace

 

[vman]

Re: OCW Fine Tuning

Confirmation and concept grasping are two different things.

To perform an OCW at 100, and then rock up to a 1000 yard match expecting the same performance, in my eyes is over confident and foolish.

As I said, no harm in confirming (besides using some components).

 

[X-fan]

Re: OCW Fine Tuning

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">SABuzzard no harm in confirming. Take that load out far and you will see any vertical dispersion really start to show up. You may find you need to tweak around with minor powder adjustments, maybe even seating depth... but by all means, confirming what you have at longer distances is a smart thing to do. </div></div>

Roger that.

OCW gives a forgiving charge and a good base for tuning, but I still run a ladder at 600-1000 (depending on where the rifle will be shooting).
I start group testing from there, while dialing bullet depth, but normally I am already in the money.

If I have learned anything over the years is that most precision techniques have some validity and we can glean a bit from all of them.