OCW test on 300m is primary depended on:
- meteorological conditions
- muzzle velocity
- spread of weapon/munition

Meteorological conditions generate errors, which are not dependent on accuracy weapon/munition.

Muzzle velocity we can measure with chrono.

Relative spread of weapon/munition is not dependent on distance.

I think, better is test on 100m with chrono.

1. values from chrono can exactly find OCW independent from spread of weapon - if loads in interval 1gr had similary speed, in this interval is OCW.

2. spread on target in distance 100m is less dependent on meterological condition and muzzle velocity. it is only spread of weapon/munition for this one charge.

In this way we can find optimal charge for minimal spread of muzzle velocity and optimal charge for minimal spread weapon/munition. It is ideal, when this two charge is equal.

I am not certain that I buy into the OCW theory. I have tried it, and found it to be inconclusive because of other factors. However, with regard to your suggestion that OCW can be determined on the basis of chronograph data, I am very skeptical for the following reason.

As I undersand the OCW theory, optimum results occurs when the top and bottom of the barrel oscillation is reached. The most consistent velocities as revealed by the least change in velocity, ie, the lowest std deviation, are generated by another group of variables unrelated to barrel oscillation. Therefore, we may frequently achieve our best accuracy at a velocity that does not have the lowest Std Deviation.

If the two came together, you would truly have a nice load, but the load with the lowest Std Deviation is not necessarily the most accurate load.

Regarding the range at which one should conduct the tests, if you are dealing with very accurate rifles, testing at 300 yds may be necessary to determine any differences in loads. I agree with you that at 300 yds, other environmental issues begin to come into play.

I want to try OCW again, and test out the theory with a rifle which I know is extremely accurate. I think that seating depth also has a profound impact upon accuracy, and that it can change and improve an already good load. Ku-dude

[ 02-06-2003, 06:28: Message edited by: Ku-dude ]

"If the two came together, you would truly have a nice load..."

And that's the way of it.

I originated the term OCW (meaning optimal charge weight), to describe the amount of powder in a particular load application that ignites and burns more consistently than any greater or lesser amount of that powder.

For example, you're developing a load for the .270 Winchester using a 130 grain Sierra Gameking bullet and IMR 4350. There is a specific amount of IMR 4350 that will ignite and burn more consistently than any greater or lesser amount of IMR 4350. (55 grains in this case )...

The harmonics of the barrel, and their effects on the group, must be ignored during initial OCW load development. That is one reason that the initial OCW test is fired at 100 yards, rather than at 300. In the initial stage, you're only concerned with finding that specific amount of powder that ignites and burns most evenly. Barrel harmonics will affect the sizes of the groups during this stage, but that is fixable...

Once you find the OCW, you can then tune the load to coincide with the barrel's best harmonic node by mere seating depth adjustments. Then you have the best of both worlds, so to speak...

Volk is actually onto something with the chronograph data. However, chronographs can err (according to their own specifications) up to around 2 percent or worse, so unless you've got a perfect chronograph (assuming one exists) I think it is easier to simply shoot the charge graduations, in round robin fashion at 100 yards, and identify three consecutive groups with a common point of impact. Choose the center group's charge, and you have the tentative OCW. It will require tuning by seating depth adjustments, and proofing at whatever maximum range the load will be used at.

Ku-dude, if you recall, what cartridge, bullet, and powder were you using when trying my load development method? And what charges did you use for the round robin firing?

Dan

788,
It was a 180gr BT. The powder charge was probably 4350 or 4831. The round was 300HH, and the problems were rifle set up. I cannot get to my data at this point. Ku-dude