OCW Test, thoughts please...

[gmelahn]

kay this was my first time trying the OCW meathod for working up a
load, I was wondering if I could get a little input on what I'm looking at and where to go
from here. I was at an outdoor range, 100 yards, about 7 at night . I had to rush my last
two strings of fire because I was running out of sunlight. Also I just got done
remounting my scope and I had to re-zero and never really got it perfect; thats why the
groups are high left so please take that into account. I started to notice slight pressure
signs at 46grns which increased at 46.5. Please let me know if you need any more info.

Components
Rifle: Savage 10FLCP-k, 1-10vtwist, 24" barrel
Bullet: SMK 168
Powder: Varget
Case:Federal GMM( don't get upset with me about for using federal cases)
Primer CCI200
OAL(ogive) 2.211 .020 off the lands

Weather
Temp: 90F
Wind: SW7mph from 5 o'clock
Pressure: 29.8

Thanks,

G-

 

[RonAKA]

I see lots of numbers and appreciate your detail in tracking things. However, the number that I think is most important seems to be missing. For each group I would like to see the vertical only distance from your aim point to the centre of the group. Next I would plot the vertical distance vs the grains of powder. What you are looking for is a range of powder weights which do not make a lot of difference in vertical distance. If you make a plot then this should show up as a bit of a flat spot, as the grains of powder go up, but vertical distance to the center of the group does not go up as fast.

Your groups are moving up and to the left as powder weight increases. This in my experience is very normal for a barrel that has a right hand twist. More velocity elevates impact, and also twists the gun (especially if it is not well secured in the rests) counterclockwise and as a result to the left.

However, what you are looking for is just the elevation effect, so that is why you need to extract out the vertical center of each group.

By the way, I thinks the groups are great, and you should learn something from the result.

 

[gmelahn]

Below is the vertical dispersion:

43.4......0.365”
43.8......0.642”
44.2......0.762”
44.6......0.786”
45.0......0.965”
45.5......1.232”
46.0......1.585”
46.5......1.900”

Thanks for your help

 

[RonAKA]

I see a flat spot at about 44.2 to 44.3 grains.

 

[gmelahn]

Sweet graph, now thats what I'm talkin' about! I need to make one of those. Its nice to see the flat spot in the vertical dispersion.

 

[gmelahn]

Here is the latest, today was windier full value left to right at about 7 MPH. I have been told pushing 45 looks the best. I think I'm going to load 44.8 or 44.7 and start playing with the seating depth. Unless that is someone has any other suggestions.....

 

[Erik Cortina]

I see a flat spot at about 44.2 to 44.3 grains.

Now, would you mind telling us how to create that graph?

 

[Steve Blair]

You can do that in Excel by graphing two variables. The upper graph shows two bullets, charge weight vs. velocity. The lower graph shows the same two bullets, seating depth against group size. Trends are often easier to identify visually.

 

[squirrelduster]

Excellent post.
Great information!

 

[TestPilot]

G- The OBT node 5 for a 24" barrel is 1.2282 ms. Quickload shows this being produced with 44.36 grns of Varget at 2625fps MV...I couldn't tease out your actual COAL (base to Tip) from the info you posted so I tweaked seating depth (Quickload seating depth not ogive based...). Bottom line is your data seems to line up well with Node 5...Node 4 is at 1.1016 ms but based on your mention of pressure concerns, don't think you can get there. If you posted your actual COAL I could get a more accurate calculation...