Help with deciphering OCW test results

[Airw4ves]

First off, if this in in the wrong area, please feel free to let me know or move it.

Now, I took information from a few different sources and came up with the OCW test being the best. So off to the range I went.
My rifle is a 6.5x47L with 24" barrel 1/8 twist.
I am using 140gr Barnes Match Burner bullets and Varget powder. All chrono data taken with a Magnetospeed Sporter. The test was shot at 100m. Each was shot in a three shot string with position being rebuilt between.

Any help on which area to work on would be appreciated as Im not really sure what Im looking for with "finding the node".
Thanks

 

[redbullitt]

Personally I like to shoot mine a bit further out. Makes the nodes stand out better, and be easier to see. If you and the rifle and ammo are capable (looks like you are btw), go to 200 or 300 next with the better loads.

Provided conditions are good and youre shooting cleanly, you should find that while progressing through the charge weights (remember shooting and conditions are the same as possible) you should see some groupings that are notably better and some that are notably worse even though you did not botch the shot.

I try to find something with good SD, minimal vertical stringing consistently at the velocity I need for whatever cartridge I am working with. Sometimes you have to compromise, sometimes not.

I bet there is a low node under 35g, then it opens up, then starts tightening up at 37.4g again. Mind you, this is assuming your shooting is good to go on ALL groups.

I like the last two groups on the hotter end. Any pressure signs?

IF you have enough range, consider a ladder test as a preliminary step before ocw testing too. It can help you hone in a little quicker on the charges you should focus on. I generally do this first if possible, then move to a test like yours with the most promising charges. After that I take the best out to 300 or 400 yards to see what it does, tHEN adjust seating depth at distance. Usually works pretty well, thought ymmv

I would load up some 5 shot groups just above and below your 37.7 charge(depending on pressure of course), and take it to 200 or 300 yards if you can.

 

[Sheldon N]

Your velocity is very linear, not much flattening of the curve at any charge weights. Your SD across all groups is acceptable, mostly single digit. All the groups seem pretty good to me, especially the upper end. You've got very consistent POI in the 37 grain range. If it were me I'd load at 37.5 or 37.6 and call it a day. Might not be a bad idea to test out a charge weight or two above 37.7 to see if pressure signs are lurking or if the group POI shifts or the group opens up. That would be good to know for how the load will shoot in the hotter summer weather and how much leeway you have on the top half of that upper node. If 38 grains is also the same POI as 37.7 with no pressure signs then I'd probably favor 37.7 over slightly lower since it's shooting bugholes for you.

 

[Airw4ves]

Nearest range to me is max 200m so I'll give that a go here next days off. Being the first time reloading and shooting this gun I wanted to start pretty low (not according to Hornady's lawyers mind you) and work from there. Might load up 37-38 in .1 gr incriments for my next one. Then once I get those results move out to the farther range (its 1.5hrs away)

 

[jsthntn247]

Do a seating depth test at 37.6 and be done with it.

 

[padom]

Shoot 37.5-38.3 in .2g increments to see of your POI stays the same or changes. Repost those results.

Also, youre supposed to shoot an OCW test "Round Robin" style, meaning one shot of each charge weight at its target till you shot all your charge weights then start over. Not 3 shot strings of each charge weight..

 

[padom]

Do a seating depth test at 37.6 and be done with it.

I sure wouldnt do this without knowing what happens above 37.7... Could be right on the edge of the node. Higher temps, different lot of powder, or charges off by .1g could push you out of the node if your are on the edge.

 

[Brentc]

Based on some calculation from the scatter node at 35.9 and viewing your results, there is an obvious node between 37.1 and 37.7 which is as large as it theoretically should be and 37.4 and 37.5 are right in the middle. I think you'd have a very forgiving load at 37.4 or 37.5. It may not be the most accurate every day, but it would be the most consistent over time.

 

[Marksman10x]

37.5

 

[Skoalman]

Question for the OP. What are you doing to get your chronograph data? Sorry if that's a silly question but I can't figure out how you get your SD and velo if you are shooting the OCW round robin style....maybe is was 3 shot groups.

 

[MachoKing]

The formula for SD is very simple. Square root of (X-x')[SUP]2[/SUP] over n. X being the velocity of one shot, x' being the mean of all shots in the group, n being the number of shots in the group. Maybe he is hand calculating it, so he just records the velocity of each powder charge and when the round robin is finished he hand calculates.

 

[Airw4ves]

Question for the OP. What are you doing to get your chronograph data? Sorry if that's a silly question but I can't figure out how you get your SD and velo if you are shooting the OCW round robin style....maybe is was 3 shot groups.

As MachoKing stated, I'm noting the number of each shot on my Magnetospeed's display and when I get the emailed spreadsheet of values, inputting them into a SD Calculator (google has a bunch of sites). I wrote the charge weight on each of my cases too for easier identification.
I unfortunately did not shoot round robin this time (got 10 shots in and realized Id screwed that up), but will when I go back and test 37.0-38.0 in 0.1 increments. Also will be pushing out to 200m hopefully.

Thanks for all the feedback! This is making it much easier and way less daunting to get into reloading/load development.

 

[JRM]

I don't mean to detract from your topic Airw but I'm currently doing OCWs on my Ax308 and am having trouble identifying what everyone else is seeing in these tests.
My one of many questions is; are horizontal strings considered acceptable within reason compared to vertical strings which could show barrel harmonics in action? I'm seeing 37.1 to 37.7 as you guys have mentioned, hence the 37.5 load to be "forgiving" load in this instance.

 

[Airw4ves]

No detracting at all, Im new as well so trying to learn what Im actually looking at is helpful. Means I dont have to post up pics every time I create a new load too haha

 

[CharlieNC]

Air the objective of the ocw and ladder tests is not to look at group size, but to find the node where the differences you made in charge weight or seating depth result in the least change on the point of impact. This is achieved when the barrel harmonics are optimum, and result in best long range accuracy. Resulting group size should also be close to optimum, but other factors affect that as well.

 

[Deleted member 10043]

I don't mean to detract from your topic Airw but I'm currently doing OCWs on my Ax308 and am having trouble identifying what everyone else is seeing in these tests.
My one of many questions is; are horizontal strings considered acceptable within reason compared to vertical strings which could show barrel harmonics in action? I'm seeing 37.1 to 37.7 as you guys have mentioned, hence the 37.5 load to be "forgiving" load in this instance.

That is because it is all "harmonic" related Internet voodoo magic. Contact this guy. He is very knowledgeable on OCW and other methods.

 

[TripleBull]

Contact this guy. He is very knowledgeable on OCW and other methods.

Rumor is his momma broke him in as an infant by throwing him face first into the gravel.

 

[padom]

LOLOL. It seems to be broken in..

 

[JRM]

That is because it is all "harmonic" related Internet voodoo magic. Contact this guy. He is very knowledgeable on OCW and other methods.

So I need to drag my rifle to the range behind my truck and that should take care of any issues?
Who knew it was that easy.



Sent from my iPhone using Tapatalk

 

[Deleted member 10043]

He also Krylon spray paints his Kimbers metallic gold or coast guard orange from end to end. The whole thing. He has proven it doesn't affect accuracy.

 

[Airw4ves]

Update on load development.
loaded up 37.0-38.0 in 0.1 grain incriments, and shot round robin style at 200m
These are my results. I haven't calculated SD for each group yet.

 

[Devildog]

When I was trying to do the OCW test on a few loads I found it really helpful to contact Dan Newberry, as you know he invented the OCW and for $45 he will work with you as long as you need to get an accurate load. Plus he is a wealth of information and a super nice guy. pay him to help you with one load and by the time your done you'll have a good understanding of the OCW system. From then on you'll be an old pro! Good luck http://optimalchargeweight.embarqspa...ing/4568639027

 

[Airw4ves]

Damn, that sounds like a great deal
May have to take him up on that
Thanks!

 

[Brentc]

At 200 yards they become more difficult to read, however I see a scatter at 37 and 37.1. Plus, the POI is relatively the same between 37.2 -37.8 so I'd say 37.5 or 37.6 is your accuracy node. Tune seating depth to get rid of the vertical and you'll be set.