Interpreting OCW (OPTIMAL CHARGE WEIGHT) results
10-05-2016, 10:28 AM
#1
Banned
Thread Starter
Join Date: Mar 2007
Posts: 388
Interpreting OCW (OPTIMAL CHARGE WEIGHT) results
I've tried the "OCW" (OPTIMAL CHARGE WEIGHT) method of working up a load. I like what I see in #8, and a couple others. But the instructions from Dan Newberry are kinda fuzzy. I'm supposed to ignore 'close' patterns and triangulate the shots to determine the distance of the center of the triangle to the target center??!!
Doesn't make sense. Why would I ignore the fact that the shots on #8 are sub 1 MOA (3/4") and go with another pattern.
Any help here would be nice. Maybe I should go back to the "Ladder" method.
Doesn't make sense. Why would I ignore the fact that the shots on #8 are sub 1 MOA (3/4") and go with another pattern.
Any help here would be nice. Maybe I should go back to the "Ladder" method.
Last edited by dig4gold; 10-05-2016 at 01:13 PM.
10-06-2016, 09:55 AM
#2
Nontypical Buck
Join Date: Oct 2009
Location: Kansas
Posts: 3,903
OCW method, at its purest, has absolutely nothing to do with group size, and absolutely nothing to do with POI truth to POA. All you're trying to do is identify a window of powder charges which produce the least vertical dispersion due to variance in actual powder throw weight. In other words, all you're doing is looking at the variation from one group to another for vertical position relative to the POA.
Cut your target in half and put the bottom half beside the top so your POA's are all in line - that's the way an OCW target should be done, otherwise, it's difficult to interpret the results when the shots aren't strung above the same horizon.
After doing so, what you should be looking for is vertical displacement from one groups center to the next - meaning when you look at each group compared to its neighbors, are they all centered together, or are your groups riding a wave? When I did OCW (purely), I drew a line below the targets and measured up from the line to be able to track that "wave motion".
As Dan instructs, If you have a group that's two shots together then one spread away like :. you can't say the two shots are the group. I don't take the time to draw triangles and find the Centroid, I just pick approximately the center of the largest spread, and spike that as my actual average POI. You'll see below where the yellow line I drew passes through the groups - about in the middle of all 3, NOT distracted by the close together impacts.
So this is what you get:
At the left, between 1 and 4, there's a lot of noise, then at the right, 8 takes a pretty big jump up again. However, between 5 and 7 is very stable (with a respectable nod towards the left side 4).
IF YOU SUBSCRIBE TO THE OCW THEORY - then based on this target you should load between 43.7 and 44.0grn, closer to 44.0, since it's basically flat between 5 and 6, raising slightly towards 7, and falling slightly toward 4.
I'd probably load up another set in that range and shoot 5 shot groups.
In theory then, if you tune up the seating depth, you'll be able to tighten up those groups at that powder charge.
At least that's the theory...
Cut your target in half and put the bottom half beside the top so your POA's are all in line - that's the way an OCW target should be done, otherwise, it's difficult to interpret the results when the shots aren't strung above the same horizon.
After doing so, what you should be looking for is vertical displacement from one groups center to the next - meaning when you look at each group compared to its neighbors, are they all centered together, or are your groups riding a wave? When I did OCW (purely), I drew a line below the targets and measured up from the line to be able to track that "wave motion".
As Dan instructs, If you have a group that's two shots together then one spread away like :. you can't say the two shots are the group. I don't take the time to draw triangles and find the Centroid, I just pick approximately the center of the largest spread, and spike that as my actual average POI. You'll see below where the yellow line I drew passes through the groups - about in the middle of all 3, NOT distracted by the close together impacts.
So this is what you get:
At the left, between 1 and 4, there's a lot of noise, then at the right, 8 takes a pretty big jump up again. However, between 5 and 7 is very stable (with a respectable nod towards the left side 4).
IF YOU SUBSCRIBE TO THE OCW THEORY - then based on this target you should load between 43.7 and 44.0grn, closer to 44.0, since it's basically flat between 5 and 6, raising slightly towards 7, and falling slightly toward 4.
I'd probably load up another set in that range and shoot 5 shot groups.
In theory then, if you tune up the seating depth, you'll be able to tighten up those groups at that powder charge.
At least that's the theory...
Last edited by Nomercy448; 10-06-2016 at 03:31 PM.
10-06-2016, 04:22 PM
#3
Nontypical Buck
Join Date: Oct 2009
Location: Kansas
Posts: 3,903
Since you mentioned thinking about going back to a Ladder Test - this might be interesting to you.
I don't personally subscribe to either philosophy by the letter, and I honestly consider comparing both methods to be one of those "distinction without a difference" type practices. They really do the same thing, just with a different target shape.
I was bored this evening, so I converted your OCW target to a ladder test by placing dots over all of the bullet holes, then superimposing them all onto one target as if they were all fired at the same POA, then assessed for elevation changes with changing powder charge. I placed a box around each group to determine where the center elevation for each would be, then placed its respective coloured line and indicating number.
So in this picture, you get the same result: There's a lot of elevation change bouncing back and forth between 1, 2, 3, and 4 as you raise the charge weight, then things seem to hold pretty stable between 4, 5, 6, and 7, with a big jump in elevation again between 7 and 8. So just like in the OCW assessment, shooting this as a Ladder Test would have shown the same preference for dropping somewhere between 5 & 6.
I don't personally subscribe to either philosophy by the letter, and I honestly consider comparing both methods to be one of those "distinction without a difference" type practices. They really do the same thing, just with a different target shape.
I was bored this evening, so I converted your OCW target to a ladder test by placing dots over all of the bullet holes, then superimposing them all onto one target as if they were all fired at the same POA, then assessed for elevation changes with changing powder charge. I placed a box around each group to determine where the center elevation for each would be, then placed its respective coloured line and indicating number.
So in this picture, you get the same result: There's a lot of elevation change bouncing back and forth between 1, 2, 3, and 4 as you raise the charge weight, then things seem to hold pretty stable between 4, 5, 6, and 7, with a big jump in elevation again between 7 and 8. So just like in the OCW assessment, shooting this as a Ladder Test would have shown the same preference for dropping somewhere between 5 & 6.
10-11-2016, 06:12 AM
#4
Nontypical Buck
Join Date: Oct 2009
Location: Kansas
Posts: 3,903
After a few days, I'm feeling a little itchy - I know that was a lot of text, but wanna be sure it makes sense. There seems to be a lot of confusion on these methods, and even larger debate whether they have merit at all. Hopefully my posts above helped at least reduce confusion?
10-11-2016, 08:35 AM
#5
Boone & Crockett
Join Date: Jan 2004
Location: Eastern PA
Posts: 12,746
Nomercy - that's very interesting. So let me see if I understand this. Because if I were to go about my usual method of loading various charges and shooting for group, I would have settled on #8 and been fat dumb and happy.
So they way I understand what you're saying is that I should concentrate on loads 5-7 and play with seating depth. This should give me tighter groups (tighter than #8)?
Why not tinker with seating depth with the charge from group 8 first?
So they way I understand what you're saying is that I should concentrate on loads 5-7 and play with seating depth. This should give me tighter groups (tighter than #8)?
Why not tinker with seating depth with the charge from group 8 first?
10-11-2016, 05:13 PM
#6
Nontypical Buck
Join Date: Oct 2009
Location: Kansas
Posts: 3,903
If a guy subscribes to the theory..........
Powder dispensers, whether mechanical throwers or automated scales or even balance beams are not perfect, so a charge of "44.0" might actually be 43.9 or 44.1, or maybe even 43.85 vs. 44.14, or maybe even worse. The range 1-4 is a prime example of where NOT to load, according to OCW theory, as the variability in charge weight will create greater variability in elevation. So the goal in this type of test is to find the "forgiving spot" where changes in charge weight make the least change in elevation dispersion.
Of course, if you're not shooting long range where vertical dispersion starts to matter, it really doesn't make a difference.
Moving from these, if you want to spend your life in load development, I'd load more in the range where the dispersion is flat, and see if I can tighten groups with seating depth. If they don't, then in theory, try a different bullet or even bullet weight. If nothing tunes, run a different powder to see if the "window" might match up with the velocity for the particular bullet (targeting the window where the velocity would be near #8 with that particular bullet).
Like I said - I don't necessarily subscribe whole hog to this method, or any other, not even my own. I find a load which shoots small groups, I shoot it. But I often go through the motions of ladder or OCW tests along the way to see if there's something I can learn to make them even better.
Powder dispensers, whether mechanical throwers or automated scales or even balance beams are not perfect, so a charge of "44.0" might actually be 43.9 or 44.1, or maybe even 43.85 vs. 44.14, or maybe even worse. The range 1-4 is a prime example of where NOT to load, according to OCW theory, as the variability in charge weight will create greater variability in elevation. So the goal in this type of test is to find the "forgiving spot" where changes in charge weight make the least change in elevation dispersion.
Of course, if you're not shooting long range where vertical dispersion starts to matter, it really doesn't make a difference.
Moving from these, if you want to spend your life in load development, I'd load more in the range where the dispersion is flat, and see if I can tighten groups with seating depth. If they don't, then in theory, try a different bullet or even bullet weight. If nothing tunes, run a different powder to see if the "window" might match up with the velocity for the particular bullet (targeting the window where the velocity would be near #8 with that particular bullet).
Like I said - I don't necessarily subscribe whole hog to this method, or any other, not even my own. I find a load which shoots small groups, I shoot it. But I often go through the motions of ladder or OCW tests along the way to see if there's something I can learn to make them even better.
