Yeah, well, it's been my experience that reality has a nasty habit of not cooperating with the theoretical. As it is, I really don't like this notion of using the center of the group (average POI) as an indicator - the group may be 10" wide and you wouldn't know.
Load Development - The Ladder Method
- Thread starter Ganderite
- Start date
Yeah, well, it's been my experience that reality has a nasty habit of not cooperating with the theoretical. As it is, I really don't like this notion of using the center of the group (average POI) as an indicator - the group may be 10" wide and you wouldn't know.
Let me go over this in detail.
I loaded 20 rounds in Lapua brass (I really did 35, but forget about the second target for this example). The first five were just fowler shots that were also used to get me in proximity to the target. They were the middle charge. I fired those to foul the bore and then adjusted my zero to get the groups close to the bullseye, but not on it (didn't want to obscure it). From this point on, I NEVER touched the turrets.
Now, I have 15 rounds left. 3x 44.1, 3x 44.4, 3x 44.7, 3x 45.0 and 3x 45.3
I start shooting those at the target in a round robin sequence. This means I shot a 44.1 at tg#1, then a 44.4 at tg#2... then a 45.3 at tg#5 (one on each target). Then I start over at 44.1 on tg#1 again and repeat the sequence twice more. I always let the barrel cool between each and every round. I'm NOT shooting all the rounds for each charge all together. This is important. This way things like fouling and wind are distributed to each group and do not bias any one individual group.
I get this target:
Now, I examine the Target. I look for the scatter group. I see it at 44.4 gr. There should be 3 groups after it (in sequence) that have the center point in about the same location. And there they are: 44.7, 45.0, 45.3. I choose 45.0 as the OCW.
When I plot the center point on a chart (to make them more visual), I get this, which also includes higher charge weights that I left out of this example:
Notice the loop these charges from and the associated velocities.
Now, just for fun (and because I have different brands of brass) I ran the numbers in Quickload and figured out what charges gave the same velocities in Hornady brass. I do the OCW sequence again and get this:
See the scatter group at 45.2. Here the OCW is at 45.8. Makes sense, Hornady brass has a larger internal capacity. My center point plot looks like this:
Notice the loop is formed by the same velocities?
If I put them together on the same chart:
They land in virtually the same location. I have found the OCW for a given load with two different brands of brass. The fact that it is not only repeatable, but repeatable with different brass speaks volumes.
I loaded 20 rounds in Lapua brass (I really did 35, but forget about the second target for this example). The first five were just fowler shots that were also used to get me in proximity to the target. They were the middle charge. I fired those to foul the bore and then adjusted my zero to get the groups close to the bullseye, but not on it (didn't want to obscure it). From this point on, I NEVER touched the turrets.
Now, I have 15 rounds left. 3x 44.1, 3x 44.4, 3x 44.7, 3x 45.0 and 3x 45.3
I start shooting those at the target in a round robin sequence. This means I shot a 44.1 at tg#1, then a 44.4 at tg#2... then a 45.3 at tg#5 (one on each target). Then I start over at 44.1 on tg#1 again and repeat the sequence twice more. I always let the barrel cool between each and every round. I'm NOT shooting all the rounds for each charge all together. This is important. This way things like fouling and wind are distributed to each group and do not bias any one individual group.
I get this target:
Now, I examine the Target. I look for the scatter group. I see it at 44.4 gr. There should be 3 groups after it (in sequence) that have the center point in about the same location. And there they are: 44.7, 45.0, 45.3. I choose 45.0 as the OCW.
When I plot the center point on a chart (to make them more visual), I get this, which also includes higher charge weights that I left out of this example:
Notice the loop these charges from and the associated velocities.
Now, just for fun (and because I have different brands of brass) I ran the numbers in Quickload and figured out what charges gave the same velocities in Hornady brass. I do the OCW sequence again and get this:
See the scatter group at 45.2. Here the OCW is at 45.8. Makes sense, Hornady brass has a larger internal capacity. My center point plot looks like this:
Notice the loop is formed by the same velocities?
If I put them together on the same chart:
They land in virtually the same location. I have found the OCW for a given load with two different brands of brass. The fact that it is not only repeatable, but repeatable with different brass speaks volumes.
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In practice, you will find that the groups with similar center points are usually the smaller ones. They are leaving the muzzle when it is the most calm, so it makes perfect sense that they are grouping tighter and landing in the same location. That's the whole point of OCW: the load still groups well and in the same location even with variations in your shots. This is the whole reason for finding the OCW node.
Variations may come from a variety of sources, such as temperature, fowling, etc...
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Not a problem. An important thing to remember when carrying this out is to take your time and not be rolled over by small groups that may occur in other locations. These are only three shot groups, there is still a certain amount of randomness here. I didn't perform this in the best weather for load testing either (just look out the window).
Also, the second step in this process (once you identify the OCW) is to try varying the seating depth to further shrink the groups.
In the end, you should be able to fire a 9 shot group with 3 of the rounds 0.3 gr. above the OCW, 3 round with 0.3 gr. below it, and 3 rounds on it and still produce a decent group. That's the goal. That shows that you have a very robust load.
Also, the second step in this process (once you identify the OCW) is to try varying the seating depth to further shrink the groups.
In the end, you should be able to fire a 9 shot group with 3 of the rounds 0.3 gr. above the OCW, 3 round with 0.3 gr. below it, and 3 rounds on it and still produce a decent group. That's the goal. That shows that you have a very robust load.
