Thread: OCW Load Testing

here are the notes I send out to guys starting with OCW:

Optimal Charge Weight is a technique for doing load development, that is based on the accuracy nodes that occur as a result of barrel harmonics. It is a very good way to find what load works for your specific rifle.
For the sequence below I am using the example of a 308 155gr projectile and ADI 2208

Find the max load for the powder/projectile weight combination you are using - 47gr.
Subtract 10% (multiply by 0.9) - 42.3gr. This is test round 1, load 1 of these.
Add 2% - 43.1. This is test round 2, load 1 of these.
Add 2% - 44.0. This is test round 3, load 1 of these.
Add 2% - 44.9. This is group A, load 3 of these.
Add 0.7% - 45.2. This is group B, load 3 of these.
Add 0.7% - 45.5. This is group C, load 3 of these.
Add 0.7% - 45.8. This is group D, load 3 of these.
Add 0.7% - 46.1. This is group E, load 3 of these.
etc, until you get to the published max load.
For 308 you normally end up with 0.3gr gaps between the different test groups.

Now seat all your projectiles to a standard length. Just measure some factory ammo with a comparator and go with that.

Shoot test round 1, 2, and 3, and look for pressure signs. These are also to make sure you are getting close to your point of aim (adjust your scope if necessary)

You need as many targets as you have groups. In my example, you have groups A to H, so 8 targets. I simply use blank A4 sheets with red dots stuck into the middle.
Shoot 1 round of group A at target A.
Shoot 1 round of group B at target B.
etc
DO NOT ADJUST YOUR SIGHTS. Aim at the dot, and dont worry about not hitting it.

Let the barrel cool down between shots.

Because of the increase in velocity, you should see the point of impact climb as the loads increase. This might be a diagonal climb, not necessarily vertical.

What you are looking for, is the 3 loads, where the horizontal movement slows down. This is a node. Your optimal charge weight is the load in the middle. This is the load that should give you the best consistent accuracy. There may be several nodes...

Now you can start by loading different groups for varying seating depths. You should find that your group sizes shrink (or expand) for different seating depths. Because of magazine constraints, you may not be able to always load with a seating depth just off the lands.
Additional reading:

The original instructions
OCW Overview - Dan Newberry's OCW Load Development System

Notes about harmonics and barrel timing
Optimal Barrel Time Paper