Reading OCW targets for 6.5 and .308 "redux"

[Lefty Trigger]

This is part two of my original thread here... http://forum.accurateshooter.com/threads/reading-ocw-targets-for-6-5-and-308.3961357/ taking advice and making my target a flat line. Both the 6.5 Creedmoor and the .308 targets are the higher charge weights of the original loads. The 6.5 starting load is 36.8 up through 38.0 and the .308 is 40.6 up through 42.0. While I can see the reason for the "flat line" target I'm still have a hard time seeing exactly what you guys (than can read these) see? On the .308 I'm thinking that since the loads leveled off around 41.2 and 41.4 that maybe 41.3 is the load I'm looking for? The 6.5 target just dumbfounds me? I also put the ES and SD numbers on this set of targets to see if they provide additional info. I spoke on the phone personally with SPJ (really nice and helpful guy) and I think I might redo these test in ladder format instead as he helped me understand what to look for in those.

 

[rammac]

The 6.5 has a good load between the 37.4 to 37.6.
The .308 has a good load between the 41.2 to 41.4.

What I look for is the location of the center of each three round group's position in relation to where you aimed. You are looking for a powder charge that produces groups whose centers are the same distance horizontally and vertically from the point aim. SD and ES doesn't matter, in fact, that the point of the OCW process, after zeroing the load that works best you can have extreme variations in SD and ES values and still have your groups centered over your point of aim.

 

[Lefty Trigger]

The 6.5 has a good load between the 37.4 to 37.6.
The .308 has a good load between the 41.2 to 41.4.

What I look for is the location of the center of each three round group's position in relation to where you aimed. You are looking for a powder charge that produces groups whose centers are the same distance horizontally and vertically from the point aim. SD and ES doesn't matter, in fact, that the point of the OCW process, after zeroing the load that works best you can have extreme variations in SD and ES values and still have your groups centered over your point of aim.

I found that to be true on the Creedmoor shown above, some of the best groups are the worst ES and SD numbers. Normally I only use those numbers to help eliminate powders that give really poor numbers.

 

[abersfelderami]

6.5 37.8-38.0
.308 41.2 +/-.1grn

 

[Twoboxer]

6.5 37.8-38.0
.308 41.2 +/-.1grn

Agree. Hard to ignore 37.9gr.

 

[bill123]

Agree. Hard to ignore 37.9gr.

Agree, but I'd want to know what is causing such large MV spreads over 3 shots.

 

[rammac]

Agree, but I'd want to know what is causing such large MV spreads over 3 shots.

Wished I knew, that high OCW node is good but the ES values are really surprising considering how tight the groups are. I'll be watching for a reasonable response, I hope somebody can come up with a good explanation that's verifiable.

 

[Twoboxer]

Agree, but I'd want to know what is causing such large MV spreads over 3 shots.

Understood. But perhaps more important is what's going on to deliver six consistent POIs across a 0.3gr spread despite that. The numeric difference between the groups' stats may tighten with a larger sample size.

ETA: For example, in your first thread 37.4gr showed V=2633 while your second thread shows 37.2gr with V=2651.

 

[Lefty Trigger]

If somebody can figure it out I would like to know as well and I'm the one that shot them!! All this data is from a ultra reliable LabRadar unit. I am getting way better ES/SD numbers going back to my method of Lee powder dippers and my trickler and some of these threw me for a loop with such low numbers. Not sure why some of the better groups are with crazy spreads though? If you click on the link to the first part it contains the "lower" half of the test but I did not put numbers on the targets for ES/SD.

 

[Lefty Trigger]

Understood. But perhaps more important is what's going on to deliver six consistent POIs across a 0.3gr spread despite that. The numeric difference between the groups' stats may tighten with a larger sample size.

ETA: For example, in your fist thread 37.4gr showed V=2633 while your second thread shows 37.2gr with V=2651.

The numbers are closer on the .308 than the Creedmoor, I don't know for sure but there was a huge temp swing from the last test to this test with the temp being hotter yesterday than last week. Yesterday it was close to 90 on the range and last week when I shot the first test it was in the middle 70's,...maybe??

 

[Bc'z]

Agree. Hard to ignore 37.9gr.

What he said

 

[Boatschool02]

Maybe I missed it. What range?

 

[jr600yd]

Several things can cause your SD and ES spread. Neck tension sure but are you using new cases that haven’t been fireformed? Same lot of cases?, Primers?, powder?
You will get better readings if you increase the range. If you can go to 600 - 1K you’ll really see a difference.

 

[Lefty Trigger]

Maybe I missed it. What range?

100yds...

 

[Lefty Trigger]

Several things can cause your SD and ES spread. Neck tension sure but are you using new cases that haven’t been fireformed? Same lot of cases?, Primers?, powder?
You will get better readings if you increase the range. If you can go to 600 - 1K you’ll really see a difference.

These loads are with prefired brass, 6th reload and annealed on the 4th reload, primers the same but this is a new powder for both guns that's why I'm testing it.
Here in Ohio getting beyond 300yds is like finding a brick of gold in your driveway. No way to practice or test on it if you don't have it. Our local club only goes to 300yds and it's available only 1 day a week from 4pm till dark and other shooters there limit your ability to go down and check/mark targets. Sorry guys but working with what I have available to me. It sucks and believe me I know it. I'm in real need of a friend with a long range in his back yard...

 

[Twoboxer]

. . . I don't know for sure but there was a huge temp swing from the last test to this test with the temp being hotter yesterday than last week. Yesterday it was close to 90 on the range and last week when I shot the first test it was in the middle 70's,...maybe??

IMO, it would be difficult to argue against what the paper shows . . . you found a 90 degree load, 37.9gr, that will serve well 100-300yds. One could make the theoretical argument that it may fall apart at ranges beyond that if the MV spread is in fact substantially different than the 37.4gr load area. Admittedly, you can't have a real ES under 15 if your 1st three shots go wider, but 3 shots does not an SD make.

If you've convinced yourself the 3-shot ES/SDs are the more important stats, then working around 37.4gr playing with seating depth may help tighten the groups. Or maybe they're good enough as is for your intended uses.

I'm not going to try to unconvince you, except to say that a thorough reading of Newberry's OCW will reveal no mention of a chrono let alone ES/SD.

 

[Zero333]

6.5cm 37.9 gr

308win 41.3 gr

 

[Bc'z]

6.5cm 37.9 gr

308win 41.3 gr

I was thinking 41.1

 

[JFrank]

I was thinking 41.1

B
What powder and Bullet combo do you prefer in your Creedmoor ??
J

 

[mgunderson]

These loads are with prefired brass, 6th reload and annealed on the 4th reload, primers the same but this is a new powder for both guns that's why I'm testing it.
Here in Ohio getting beyond 300yds is like finding a brick of gold in your driveway. No way to practice or test on it if you don't have it. Our local club only goes to 300yds and it's available only 1 day a week from 4pm till dark and other shooters there limit your ability to go down and check/mark targets. Sorry guys but working with what I have available to me. It sucks and believe me I know it. I'm in real need of a friend with a long range in his back yard...

Alliance Rifle Club, Malvern Ohio they have 1000 yards. Might be a few hours but they run monthly matches. Great people and friendly. Consider shooting a 600 yard match and do as little load testing in the process.