OCW opinions...?????

[Kampfjager]

Hey guys shot these charge weights today... 8 groups with 3 rounds... what's your opinion on the OCW? 45.3 & 46.1 looks real good....what's interesting is the corresponding groups .8 groups of are incredibly similar which tells me where the nodes are falling...... btw, these were shot round Robin style and barrel temps varied between each shot in each group....

 

[BallisticsGuy]

I'd suggest that you're doing that work too close and should consider stretching out to 200 or 300yards or more if you're going to do an OCW method. The difference results will be much more dramatic and will be trivially easy to read as a result instead of being effectively null results like you've got now. Your rifle is performing very consistently or I suspect it'd be a lot easier to read.

 

[CVCOBRA1]

Did your 46.5 or 46.7 show any pressure signs? Looks like you might just be starting to find your load. No chrono? What cal?

 

[Kampfjager]

Did your 46.5 or 46.7 show any pressure signs? Looks like you might just be starting to find your load. No chrono? What cal?

No pressure signs ..... .308.... haven't chrono'd yet, usually don't till I find a good load....
155gr lapua scenars
Varget
Lapua brass
Cci200's
OAL 2.855" (my mag lenght)

 

[CVCOBRA1]

You should use your chrono while developing a load. When your SD's start growing your usually leaving your node.

 

[Kampfjager]

You should use your chrono while developing a load. When your SD's start growing your usually leaving your node.

the 45.3 load was chrono'd and had quit a few duplicates.... that's why I've kinda used it as the standard, I'll chrono some and post results at other nodes

 

[User4302021]

Hey guys shot these charge weights today... 8 groups with 3 rounds... what's your opinion on the OCW? 45.3 & 46.1 looks real good....what's interesting is the corresponding groups .8 groups of are incredibly similar which tells me where the nodes are falling...... btw, these were shot round Robin style and barrel temps varied between each shot in each group....View attachment 130391

I printed out your target picture and did some target analysis.

First, Hodgdon's pressure data lists 47 grains as max. But they use Winchester brass. Your max based on the same pressures in Lapua brass is going to be somewhere around 46 grains. I know this may not be the same for your rifle, but it is a starting point.

I have consistently found that loads that are in the vicinity of 2% off maximum are the most consistent and tunable. I don't know your rifle, so there will be some variability. This is where we start looking at the target.

I printed out your target and drew straight lines between each group center. Then I drew a line from POA to each group center. What I see is that 45.3, 45.5, 45.7 all have virtually the same height. However, 45.5 and 45.7 also have identical angle from POA.

2% off from 46 grains is 45.1 grains.

So...
A) 45.5 is safe in your rifle
B) It is right in the immediate area I would expect a node to show up.
C) It is in the middle of 3 loads with the same vertical. (At the highest vertical to boot)
D) It "clocks" identically from POA with the load above it, so POI will most likely stay stable when it gets hot.
E) It is only 0.2 grains from a known performing load.

Given the targets you presented, 45.5 grains is where I would start seating depth testing if it were me.

 

[Kampfjager]

****, dogrocket..... that's an impressive analysis.... I'm not sure how to respond to that....

 

[Kampfjager]

I printed out your target picture and did some target analysis.

First, Hodgdon's pressure data lists 47 grains as max. But they use Winchester brass. Your max based on the same pressures in Lapua brass is going to be somewhere around 46 grains. I know this may not be the same for your rifle, but it is a starting point.

I have consistently found that found that loads that are in the vicinity of 2% off maximum are the most consistent and tunable. I don't know your rifle, so there will be some variability. This is where we start looking at the target.

I printed out your target and drew straight lines between each group center. Then I drew a line from POA to each group center. What I see is that 45.3, 45.5, 45.7 all have virtually the same height. However, 45.5 and 45.7 also have identical angle from POA.

2% off from 46 grains is 45.1 grains.

So...
A) 45.5 is safe in your rifle
B) It is right in the immediate area I would expect a node to show up.
C) It is in the middle of 3 loads with the same vertical. (At the highest vertical to boot)
D) It "clocks" identically from POA with the load above it, so POI will most likely stay stable when it gets hot.
E) It is only 0.2 grains from a known performing load.

Given the targets you presented, 45.5 grains is where I would start seating depth testing if it were me.

What do you see different between 45.3-45.7 vs. 46.1-46.5 ...????

 

[User4302021]

What do you see different between 45.3-45.7 vs. 46.1-46.5 ...????

From 46.1 to 46.7 your group centers are moving in a downward slope, and they are all clocking to a slightly different angle from POA.

46.3 and 46.5 are really close as far as the angle, but the group center is falling.

The loads that plateau when the barrel is traveling up are the ones to chase as they are the most consistent. You can Look up "positive compensation" when you have lots of time. That subject takes pages to discuss and it has been a long time since I dove into it. But in a nut shell, gravity can work with you when the barrel is at the top of it's travel. It does the opposite when at the bottom of it's travel.

Also, the loads at the upper range of pressure are almost universally narrow and finicky to tune. In the summer heat you will likely regret using them.

 

[User4302021]

Here is what I did:

Don't mind the chicken scratch at the bottom of the picture.

Notice the rise and fall of the group centers. Notice the angle of the line from POA to group center. You will typically see a pattern emerge on both axes. So you look for a flat spot at the top of the barrels travel, and then look to find a couple of groups that clock the same way.

If this same area provides good velocity and acceptable SD's then you are usually golden. All that is left is the seating depth tests.

 

[Kampfjager]

Wow.... that's an inpressive read... but what would it mean if just one of the rounds in the 45.5 group was pulled or displaced by shooter error which would cause the group center to change.... would that render your theory inaccurate, what's the percentage of accuracy only using the 3 shot groups?

 

[User4302021]

Wow.... that's an inpressive read... but what would it mean if just one of the rounds in the 45.5 group was pulled or displaced by shooter error which would cause the group center to change.... would that render your theory inaccurate, what's the percentage of accuracy only using the 3 shot groups?

It would change it some. But you would likely know that you pulled it for one, and it would show up as a small variation but wouldn't alter the macro pattern. The barrel's gross movement is over several increments like a 0.6 - 1 grain spread or something similar.

Three shot groups aren't precise enough for fine adjustment, but as I said, you are looking at a macro pattern with the OCW test. Where pulling a shot would do the most damage is with the seating depth test.

 

[Kampfjager]

I'm not saying it's right or wrong but I was told that you want to see a 3 shot group like a triangle because it shows consistency better than a strung group (horizontal or vertical).... I'm certainly learning something here