Figuring out Optimal Charge Weight

[TackDriv3r]

Sometimes I chase my tail chasing accuracy, and I am sure some of you do. I am pretty sure picking the wrong OCW is one of the reasons. When I do a load development, I see ugly groups or three holes but pick the nice one hole group as my go to load but when you see changes of temp, your one hole group is now a 3 shot group. Back to square 1!!
Perhaps you guys can help me with your opinions.

I did two OCW tests today round robin style, top line is the .308 with the IMR4064 and 168 VLD and the bottom line is the 6.5 Creedmoor with H4350 and 140 Hybrids.

If some of you OCW gurus could help me narrow my search for the OCW to pick,,,next will be the jump test. ( Seating depth test )

I looked at the top line on the target which is the .308 and chose #3 as my OCW.
As for the bottom line on the target which is the 6.5 Creed, I chose #2 as my OCW.

I see those 3 shot groups I picked which are very close on the same line and POI.

Would you guys agree? Of course the jump test is after. What do you guys pick?

I think this is a learning experience most of us could benefit when we do our load developments and learn to read OCW and pick the correct OCW.

 

['Freak]

~ #4 on top row and ~ #3 on bottom row, if I gotta pick from 'em.

What, more exactly, are you shootin', what's your setup, and what's the distance ...?

 

[Twoboxer]

It's easy to pick out the best group, but that's not what this method is about at this point.

Top Row: There's a shift in POI from 43.3 to 43.6. 43.6 and 43.9 share the same group POI while 44.2 scatters. I'd try 43.7gr.

Bottom Row: Assuming 41.6 was not a flyer, the method says the OCW is likely about 1.5% away. I'd stay between 42.2 and 42.5 which share group POIs.

 

[Steve Ladino]

~ #4 on top row and ~ #3 on bottom row, if I gotta pick from 'em.

What, more exactly, are you shootin', what's your setup, and what's the distance ...?

Ditto

 

[zx10mike]

for me 43.0 and shoot. Looks a nice wide node and shoots better than i can read the wind.

 

[TackDriv3r]

~ #4 on top row and ~ #3 on bottom row, if I gotta pick from 'em.

What, more exactly, are you shootin', what's your setup, and what's the distance ...?

I am not into F class, just off the bench / long range shooting at targets out to 300 -1000.

 

[Depart123]

It's easy to pick out the best group, but that's not what this method is about at this point.

Top Row: There's a shift in POI from 43.3 to 43.6. 43.6 and 43.9 share the same group POI while 44.2 scatters. I'd try 43.7gr.

Bottom Row: Assuming 41.6 was not a flyer, the method says the OCW is likely about 1.5% away. I'd stay between 42.2 and 42.5 which share group POIs.

My assessment exactly.

 

[TackDriv3r]

This is the velocity for the above loads. Used a Oheler P35.

.308:
1. 2705-2697-2685
2. 2716-2715-2711
3. 2740-2718-2735
4. 2740-2734-2737
5. 2766-2753-2761
6. 2772-2771-2764
7. 2791-2810-2733

6.5 Creedmoor
1. 2698-2728-2739
2. 2714-2742-2752
3. 2749-2751-2758
4. 2768-2773-2779
5. 2773-2807-2811

 

[TackDriv3r]

~ #4 on top row and ~ #3 on bottom row, if I gotta pick from 'em.

What, more exactly, are you shootin', what's your setup, and what's the distance ...?

Let me ask, why pick # 4 if there is a bad POI shift on # 5? I am curious, I am not a guru in reading nodes.

 

[Depart123]

This is the velocity for the above loads. Used a Oheler P35.

.308:
1. 2705-2697-2685
2. 2716-2715-2711
3. 2740-2718-2735
4. 2740-2734-2737
5. 2766-2753-2761
6. 2772-2771-2764
7. 2791-2810-2733

6.5 Creedmoor
1. 2698-2728-2739
2. 2714-2742-2752
3. 2749-2751-2758
4. 2768-2773-2779
5. 2773-2807-2811

Additionally, velocities in groups #5 & #6 overlap almost perfectly in the 308. Same for groups #4 & #5 in the creed.

 

[muleman69]

~ #4 on top row and ~ #3 on bottom row, if I gotta pick from 'em.

What, more exactly, are you shootin', what's your setup, and what's the distance ...?

Ditto for me also

 

['Freak]

Let me ask, why pick # 4 if there is a bad POI shift on # 5? I am curious, I am not a guru in reading nodes.

Not the guru either, but ...

There’s POI shift across the board though least of the shift is at #4 then #3 and runs mostly horizontal with hardly any vertical. These clusters maybe are a portion of a skinny ‘node’ that does not span far as into either of the two loadings next door, each punching even more scattered both horizontally and vertically larger clusters of impacts.

 

[dgeesaman]

Lemme ask the group what is hopefully a helpful follow-up question:
- So if it's not entirely obvious which ones are the nodes, why not repeat the entire test and see if one appears POI stable across both tests?
- If so, would you adjust anything the second time through?

 

[Metal God]

Let me ask, why pick # 4 if there is a bad POI shift on # 5? I am curious, I am not a guru in reading nodes

Perfect question because there is a shift down and that would indicate to me that is not a OCW

I actually agree with what twoboxer wrote for the most part except I'd pick straight up 42.2 as my charge . If you were to triangulate the center of groups 41.9 , 42.2 & 42.5 you'd see those are all hitting pretty much the same spot .

There might be something from 41.3 thru 41.9 leaving you the 41.6 as your OCW but that 41.6 dips down a little bit . For me to discount that set I'd have to be sure my hold was perfect . It does appear with what looks like some flyers through out the test your hold was not spot on every time . Point being sometimes the evaluation of the OCW test has as much to do with how well you were shooting as it does what's on paper .

 

[Depart123]

Lemme ask the group what is hopefully a helpful follow-up question:
- So if it's not entirely obvious which ones are the nodes, why not repeat the entire test and see if one appears POI stable across both tests?
- If so, would you adjust anything the second time through?

The one that the others are picking ( #3 & #4 ) in the 308 groups is a node. In fact, this is the area that most guys that shoot M1A's settle on because it is a lower pressure node that is easier on the op rods. But the better SD's and therefore better accuracy potential for beyond 600 yards usually lies in the higher node.

Group #3 on the creed might be a node also, but a very narrow one, and again, not at peak pressure.

 

[TackDriv3r]

The one that the others are picking ( #3 & #4 ) in the 308 groups is a node. In fact, this is the area that most guys that shoot M1A's settle on because it is a lower pressure node that is easier on the op rods. But the better SD's and therefore better accuracy potential for beyond 600 yards usually lies in the higher node.

Group #3 on the creed might be a node also, but a very narrow one, and again, not at peak pressure.

So these two nodes are a slower node and there is a faster node? If so, at what speeds do you predict the higher nodes to be at? I have a 26 inch barrel.

 

[Depart123]

So these two nodes are a slower node and there is a faster node? If so, at what speeds do you predict the higher nodes to be at? I have a 26 inch barrel.

There are major nodes and minor nodes in all high pressure centerfire rifle calibers.

There are several things we look for. We look at the shape of the groups to determine the harmonic pattern of our barrel. We look for side by side groups that have a similar POI, this tells us that barrel timing is optimal. We look for small SD's so we know we will have small vertical way down range.

So, in your ladder test, or OCW, or any other method, you are looking for a series of groups that are
A) In a safe pressure range just short of maximum pressure.
B) Have same POI
C) Have low SD's
D) Shoot nice tight round groups.

Speed will have nothing to do with it. Actual speed is dependent on your individual rifle. Though there will be an optimal pressure range. The two nodes I picked out earlier seem to me to be in the optimal range. They may not produce the tightest groups, but that can be tweaked a bit with seating depth. They most likely will have the most consistent performance down range though.

Some will probably disagree, but that is the way of things.

 

[TackDriv3r]

There are major nodes and minor nodes in all high pressure centerfire rifle calibers.

There are several things we look for. We look at the shape of the groups to determine the harmonic pattern of our barrel. We look for side by side groups that have a similar POI, this tells us that barrel timing is optimal. We look for small SD's so we know we will have small vertical way down range.

So, in your ladder test, or OCW, or any other method, you are looking for a series of groups that are
A) In a safe pressure range just short of maximum pressure.
B) Have same POI
C) Have low SD's
D) Shoot nice tight round groups.

Speed will have nothing to do with it. Actual speed is dependent on your individual rifle. Though there will be an optimal pressure range. The two nodes I picked out earlier seem to me to be in the optimal range. They may not produce the tightest groups, but that can be tweaked a bit with seating depth. They most likely will have the most consistent performance down range though.

Thanks

 

[CharlieNC]

I assume you shot at 100yd. As you say to avoid chasing your tail move out to 200-300 yd and the differences will become much more pronounced and the nodes easier to identify.

 

[seymour fish]

There are major nodes and minor nodes in all high pressure centerfire rifle calibers.

There are several things we look for. We look at the shape of the groups to determine the harmonic pattern of our barrel. We look for side by side groups that have a similar POI, this tells us that barrel timing is optimal. We look for small SD's so we know we will have small vertical way down range.

So, in your ladder test, or OCW, or any other method, you are looking for a series of groups that are
A) In a safe pressure range just short of maximum pressure.
B) Have same POI
C) Have low SD's
D) Shoot nice tight round groups.

Speed will have nothing to do with it. Actual speed is dependent on your individual rifle. Though there will be an optimal pressure range. The two nodes I picked out earlier seem to me to be in the optimal range. They may not produce the tightest groups, but that can be tweaked a bit with seating depth. They most likely will have the most consistent performance down range though.

Some will probably disagree, but that is the way of things.

Green, you know the drill. I would add that the 308 node you picket is way too narrow to warrant further exploration. Presume if a wider one, say .6 grain or better, you would take that as a recommendation to switch powder, etc