Understanding the OCW method?


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something vague
July 19, 2009, 05:20 PM
I can't seem to put my brain around this OCW method of load development. I understand what to look for and the idea behind it but the instructions for creating my set of cartridges seems weird to me.


4. Back away from the maximum charge by 7 to 10 percent, and load one test round with this charge. Add 2% to the charge weight, and load another cartridge with that charge. Load a third test cartridge with the next 2% graduation. You will use these three cartridges for sighters, and more importantly to determine pressure tolerance in your individual rifle.

5. Add another 2% or so to the charge level used in cartridge #3 of step 4, and load three rounds with this charge weight. Add .7% to 1% to this charge, and load three more. Add that same graduation again, and load three more. Continue adding the chosen graduation until you have moved ONE increment above your chosen maximum powder charge.

Doesn't this sound like you are testing the upper end of the load data? Now in my experience I have found that my most accurate rounds are coming from the lower to middle end of the load data. Maybe this test was form of load development isn't design for target shooting but geared more toward hunting? I've many great things about this test but just don't know if it would work that well with my rifles. What am I missing.

http://optimalchargeweight.embarqspace.com/

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adobewalls
July 19, 2009, 07:01 PM
There are several stable OCW "nodes" for a given charge range of a powder.

Also, most people want to get the most velocity they can while maintaining accuracy. It sounds like that is the process that is being described. It does not necessarily mean that what is being described to find that particular OCW is the most accurate, or the only OCW for that powder/bullet/barrel combination.

For example, I shoot a midrange 7mm load that has over the years proved to be very tolerant and stable. I also shoot a top end, near max (or maximum:D) .308 load that has likewise proved to be tolerant and stable over the time I have been shooting it. Both do the job I want them to do and I consider both to be OCW loads.

Hope this helps. OCW is not as complicated as it is sometimes explained.

1858
July 19, 2009, 09:36 PM
something vague, step 3 of the OCW method instructions states ...

3. Consult at least three load data sources for maximum charge weight for the powder you've selected. Powder manufacturers are the most reliable source. You must then decide on what your maximum charge will be.

Since you state that you "have found that my most accurate rounds are coming from the lower to middle end of the load data" then your maximum charge will be something in the middle of the published range. I think the procedure described in 3, 4 and 5 is overly complicated. Pick a starting load (perhaps the published starting load for you), make up five rounds, then add 0.3gr to that load and make up 5 more, add another 0.3gr and make another five and so on until you reach the maximum load (either max published or your max somewhere below that).

I use the OCW method for all of my rifles and I want the highest velocity possible either for hunting or long-range target shooting, so I'm looking for nodes at the upper end of the published load range. There isn't anything complicated about the OCW method. Its single objective is to determine what the OCW loads are (the nodes) over the load range. OCW loads are by definition less sensitive to changes in atmospheric conditions. The OCW load +/- 0.3gr should group in the same point on the target. The benefit of the OCW load is that you'll hit what you're aiming at under a variety of atmospheric conditions. This isn't important for benchrest shooters who care more about the group size than where it is on the target. F-class shooters and hunters don't get medals for tiny groups, but their shots need to be in the X-ring to count.

:)

freakshow10mm
July 20, 2009, 08:34 AM
Lot of methods for working up loads. Some safer than others. Varmint shooters have been known to start at max charge and increase charge weight until the primer falls out, then drop back .2gr and leave it. Yikes.

kelbro
July 20, 2009, 10:02 AM
Here's my take on it.

#3 - Manual average is say 50gr.
#4 - Start load (50 gr -10%) = 45gr - load one with this weight, add 2% - load one with 45.9gr, load one with 46.8gr. - Check for pressure signs
#5 - Load three with 47.7gr, load three with 48.2gr, load three more with 49.1gr, load three more with 49.6gr, three more with 50.1gr, and the next load, 50.6gr, is your 'one increment above max'. I don't have a calculator handy so check my math but hopefully you get the idea.

I have developed several great loads with OCW.

freakshow10mm
July 20, 2009, 10:19 AM
When I work up loads, I start at the start charge and work up to max charge in .5gr increments. I load 2 rounds each to read the case and test velocity. If I get to max charge and read no pressure sign, I increase in .1gr increments above that until pressure rears its ugly head. Then I back off .2gr and that's the gun max.

My uncle takes a grain off the max charge and increases in .1gr increments until pressure signs indicate.

something vague
July 20, 2009, 05:46 PM
Here's my take on it.

#3 - Manual average is say 50gr.
#4 - Start load (50 gr -10%) = 45gr - load one with this weight, add 2% - load one with 45.9gr, load one with 46.8gr. - Check for pressure signs
#5 - Load three with 47.7gr, load three with 48.2gr, load three more with 49.1gr, load three more with 49.6gr, three more with 50.1gr, and the next load, 50.6gr, is your 'one increment above max'. I don't have a calculator handy so check my math but hopefully you get the idea.

I have developed several great loads with OCW.

I would agree that this is the way the OCW method reads Kelbro. Therefore the OCW that this method is pointing to would be the node in the upper end of the load data. Right? So in theory this upper end node should be as accurate as a lower end load, which I have found in my rifles to be the most accurate. I have reached these loads through the ladder method. But after all this reading I am under the impression that I should be able to find another point in the data where the groups tighten up again as well as they are in the node I am in right now. They do make this seem more complicated than it should be, but I suppose that explaining something is much more difficult than showing someone.

adobewalls
July 20, 2009, 08:21 PM
Yes, there should be a lower optimum charge weight node - like what I do for the 7mm.

As you work up the "ladder", you see the OCW in the "flats" where velocities are consistent across several charge weight increments. Keep in mind that the OCW is not necessarily the most accurate load, but a load that is very tolerant of the normal lot to lot variations in components and changes in shooting conditions.

The fact that many OCW loads are also accurate is the bonus.

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