Thread: OCW Load Testing

Heya guys - headed out and ran a test weekend before last.

Anyone else used the OCW method?

Basically I came to the conclusion that I needed more targets to really identify any trends. Going back and starting at a lower pressure...

Thoughts?

https://thebloke.co.nz/ocw-load-testing/

nice article

Try at 300-500m to really see the trends, imo 100m is way to close and you really need a rifle/scope/shooter combo of shooting very very tight groups to get a good indication of nodes

Originally Posted by The Bloke

Heya guys - headed out and ran a test weekend before last.

Anyone else used the OCW method?

Basically I came to the conclusion that I needed more targets to really identify any trends. Going back and starting at a lower pressure...

Thoughts?

https://thebloke.co.nz/ocw-load-testing/

lower pressure as in a lighter charge in your rounds?
the round with the ejector mark,... im not sure its such a high pressure, it could be more soft brass. reason being the primer is not really flat at all.
is there any other signs?

what was that load, and velocity?

Originally Posted by bully

lower pressure as in a lighter charge in your rounds?
the round with the ejector mark,... im not sure its such a high pressure, it could be more soft brass. reason being the primer is not really flat at all.
is there any other signs?

what was that load, and velocity?

Chronograph is on the shopping list. Any suggestions for a good one?

The load that got the marks was 39 grains. Once fired Norma Brass, MUROM Primer, 2206H Powder, 150gr Nosler Ballistic Tip. (7mm08 X-Bolt).

The reloaders manual I based the load on said 40 grams - so I was thinking that the load seemed low.

The main concern was that I hadn't seen marks like that before. The primers did look ok, and the bolt didn't stick, nor did the rifle 'feel' any different with that string. I had that main mark, and another in the string with a smaller mark. I say mark, because there isn't a ridge around it. It's just 'polished' at that point. Oh, actually, now that I think about it - yes there was something else - the cartridges themselves seemed to have polished 'streaks' down the side of them as well. No bulging or so on, but noticeable. I will see if I can find the cartridge and take a photo tonight. It was only subtle.

Is the soft brass something that can develop after the first firing?

Dan himself suggested 100 yards for the testing - hence my distance - though I do agree that it's likely my shooting that's going to be the major factor. Still. Learning experience.

Originally Posted by The Bloke

Chronograph is on the shopping list. Any suggestions for a good one?

The load that got the marks was 39 grains. Once fired Norma Brass, MUROM Primer, 2206H Powder, 150gr Nosler Ballistic Tip. (7mm08 X-Bolt).

The reloaders manual I based the load on said 40 grams - so I was thinking that the load seemed low.

The main concern was that I hadn't seen marks like that before. The primers did look ok, and the bolt didn't stick, nor did the rifle 'feel' any different with that string. I had that main mark, and another in the string with a smaller mark. I say mark, because there isn't a ridge around it. It's just 'polished' at that point. Oh, actually, now that I think about it - yes there was something else - the cartridges themselves seemed to have polished 'streaks' down the side of them as well. No bulging or so on, but noticeable. I will see if I can find the cartridge and take a photo tonight. It was only subtle.

Is the soft brass something that can develop after the first firing?

Dan himself suggested 100 yards for the testing - hence my distance - though I do agree that it's likely my shooting that's going to be the major factor. Still. Learning experience.

maybe someone with a 7/08 will come in. as without doing some research im not sure what powder weights are max or not.
Im not an expert, but I had a similar problem with a factory load before I started loading. the factory loads had ejector marks primer cratering and the primer was flatter than yours, I tried to find the photos I sent to an expert but cant find them, basicly they were getting warm, but not too bad. and they looked a lot worse than yours.
iv heard the term soft brass before but for me iv never really had that problem. I guess you could change brands, or not worry to much.

but im just some guy on the internet. so don't believe everything I say, do more research and play it safe, I just hope to give you a few clues or directions to look into.
myself I don't do the ocw method, and I do everything at 100 yards or meters to start with also.

Thanks for the feedback guys. It's all appreciated.

I get dubious the moment anyone claims to know everything.

Again, because I am really just getting started, I backed off the moment I saw something strange.

One advantage of shooting at a range, is that I generally have guys either side of me who are a lot more experienced in this - so it's handy to have a quick second opinion. Though, everything with a grain of salt, because it's ultimately me behind that controlled explosion!

Originally Posted by The Bloke

Chronograph is on the shopping list. Any suggestions for a good one?

The load that got the marks was 39 grains. Once fired Norma Brass, MUROM Primer, 2206H Powder, 150gr Nosler Ballistic Tip. (7mm08 X-Bolt).

The reloaders manual I based the load on said 40 grams - so I was thinking that the load seemed low.

The main concern was that I hadn't seen marks like that before. The primers did look ok, and the bolt didn't stick, nor did the rifle 'feel' any different with that string. I had that main mark, and another in the string with a smaller mark. I say mark, because there isn't a ridge around it. It's just 'polished' at that point. Oh, actually, now that I think about it - yes there was something else - the cartridges themselves seemed to have polished 'streaks' down the side of them as well. No bulging or so on, but noticeable. I will see if I can find the cartridge and take a photo tonight. It was only subtle.

Is the soft brass something that can develop after the first firing?

Dan himself suggested 100 yards for the testing - hence my distance - though I do agree that it's likely my shooting that's going to be the major factor. Still. Learning experience.

Magnetospeed if you want to get the best. I have progressed thru F1, CEDs (including IR screens) , Oehler and the Magnetospeed is the only one that works absolutely reliably regardless of light conditions.
V3 is due soon at the NZ agent's.

You're going about OCW pretty much the correct way.

I am having problems getting a better view of the target pics on the site where you are hosting your blog, can't seem to view individual pics or zoom in...

2 questions for you:

- are you seating the primers correctly ? your "duds" could be due to not getting them seater far enough into the pocket ? alternatively try some other (decent) primers

- did you allow the barrel to cool down between strings ? so load 1, load 2, load 3, cool down, load 1, load 2, load 3, cool down ?

here are the notes I send out to guys starting with OCW:

Optimal Charge Weight is a technique for doing load development, that is based on the accuracy nodes that occur as a result of barrel harmonics. It is a very good way to find what load works for your specific rifle.
For the sequence below I am using the example of a 308 155gr projectile and ADI 2208

Find the max load for the powder/projectile weight combination you are using - 47gr.
Subtract 10% (multiply by 0.9) - 42.3gr. This is test round 1, load 1 of these.
Add 2% - 43.1. This is test round 2, load 1 of these.
Add 2% - 44.0. This is test round 3, load 1 of these.
Add 2% - 44.9. This is group A, load 3 of these.
Add 0.7% - 45.2. This is group B, load 3 of these.
Add 0.7% - 45.5. This is group C, load 3 of these.
Add 0.7% - 45.8. This is group D, load 3 of these.
Add 0.7% - 46.1. This is group E, load 3 of these.
etc, until you get to the published max load.
For 308 you normally end up with 0.3gr gaps between the different test groups.

Now seat all your projectiles to a standard length. Just measure some factory ammo with a comparator and go with that.

Shoot test round 1, 2, and 3, and look for pressure signs. These are also to make sure you are getting close to your point of aim (adjust your scope if necessary)

You need as many targets as you have groups. In my example, you have groups A to H, so 8 targets. I simply use blank A4 sheets with red dots stuck into the middle.
Shoot 1 round of group A at target A.
Shoot 1 round of group B at target B.
etc
DO NOT ADJUST YOUR SIGHTS. Aim at the dot, and dont worry about not hitting it.

Let the barrel cool down between shots.

Because of the increase in velocity, you should see the point of impact climb as the loads increase. This might be a diagonal climb, not necessarily vertical.

What you are looking for, is the 3 loads, where the horizontal movement slows down. This is a node. Your optimal charge weight is the load in the middle. This is the load that should give you the best consistent accuracy. There may be several nodes...

Now you can start by loading different groups for varying seating depths. You should find that your group sizes shrink (or expand) for different seating depths. Because of magazine constraints, you may not be able to always load with a seating depth just off the lands.
Additional reading:

The original instructions
OCW Overview - Dan Newberry's OCW Load Development System

Notes about harmonics and barrel timing
Optimal Barrel Time Paper

+1 for Magnetospeed, high on my wishlist

puffin on here has a cool mod for the F1 chrony to increase consistency, he built a fancy box with a lightsource to improve it.

I like to do a simple ladder/pressure test first to find out where the rifles pressure limit is as they can be quite variable, one rifle I have goes 2.5gn over book max & another is under book max

Not sure about any chrono that you strap to the barrel.... particularly when trying to do accuracy OCW load development...... not exactly best practice I would suggest...

No affect on accuracy (except maybe a really thin whippy barrel and then you have other issues at any rate). Done all my recent load development with one attached. Initially also set up my IR CED but no longer bother. Recently shot .15MOA group at 100yds with it attached to my 6.5x47L. Shot regularly with it attached to my 284 F Class rifle out to 800yds and no effect on accuracy. The only affect is the device causes slightly high elevation - 1.5MOA @ 800yds (actually movement away from the sensor). Much better than the variable day to day results you get with an optical chronograph which leaves you wondering if it is the chronograph, the atmospherics, ambient temperature, powder temp susceptibility and so on and so on but in most cases is the optical chronograph.

Originally Posted by ebf

You're going about OCW pretty much the correct way.

I am having problems getting a better view of the target pics on the site where you are hosting your blog, can't seem to view individual pics or zoom in...
2 questions for you:
- are you seating the primers correctly ? your "duds" could be due to not getting them seater far enough into the pocket ? alternatively try some other (decent) primers
- did you allow the barrel to cool down between strings ? so load 1, load 2, load 3, cool down, load 1, load 2, load 3, cool down ?

Ah. Tried to fix something yesterday and broke something else. Should be fixed now.

Primer Seater - yes, I think it's just a case of me needing to seat them better. I was initially a little 'light' on the press - mainly because I haven't done many of them. However, will also look at primer options. Recommendations? Also, if I change primers, will I need to restart the testing? The next lot are already primed and ready to go.

Barrel cooling. Yes. As you stated. Though in hindsight, should I probably not allow it to cool between each shot? I realised afterwards that the end of the string would always be hotter than the start. I might need to take a book down to read between shots!

I use this one, its good.
Lee Ergo Prime

I would start again if changing primers.