OCW - chrono?

[davere]

By way of example... I shot an OCW yesterday, and then chrono'ed three rounds of each charge in random order with time in between for barrel cooling. Fair warning, I'm not the best rifle shooter in the world, so I expect there's some shooter induced error in there. My chrono seems to be having issues - 5 of the charges had one velocity each with an obvious error, so those are averages of just two rounds. As discussed in this thread, that's not a great look at what the velocity is doing, just a point of info.

The particulars are:
6.5 Creedmoor
24" Bartlein barrel
Hornady brass, once fired
CCI 200 primer
IMR 4451
Nosler 140gr RDF

Temp was about 74 degrees when I started the OCW. 78 degrees when I started chrono-ing. I saw just the tiniest bit of cratering on the primer at 42.9, but otherwise no indications that I'd reached a max pressure load. Given my lower velocities, I'm thinking I'm may work into a heavier charge and see what happens.

I'm so new to this, it's not funny, and it seems like my results are pretty subtle. It seems like maybe I have a node in between 42.0 and 42.3, but I could almost make the case that everything from 41.4-42.3 centers up at about the same spot? Also, it looks like 42.6-42.9 start moving to the next node, and I might find one in the 43.2-43.5 range, assuming I don't start seeing pressure issues there? Feel free to disagree, but help me understand, so I can learn

Compare that to the velocity readings, though, and it gets all kinds of messy... Velocity has several spots to look at, but 42.0-42.3 is definitely not one of them, and it covers a lot of ground between 41.4 and 42.3...

I'm half tempted to just do the whole thing again, but with higher starting point, and see if I can do a little better behind the gun, just to see if anything gets clearer.

 

[CharlieNC]

My experience, if you shoot at 200yd the results will be more clear. Many like 100yd and others who a fixed distance (like 1000yd BR) like to shoot at the competition distance.

 

[morganlamprecht]

42.3, play with seating depth...average POI for 42, 42.3, and 42.6 is all right there around 4-5 o clock off the diamond, all that matters at this point

 

[Sheldon N]

I'm with Morgan, looking at the OCW the node seems to be right in that 42.3 range for similar POI. Looking at the chrono data the velocity flattens out between 42.3 and 42.6 so that might make me lean a bit above 42.3...maybe 42.4 or 42.5. The POI for 42.9 doesn't move much vertically, just a bit to the left so it wouldn't really be departing from the OCW node to go a touch above 42.3.

 

[davere]

CharlieNC - if I had easy access to longer distances, I would totally move to 200. Unfortunately, I have to drive a couple hours each way to do that. 100 is my only "regularly available" option.

Thanks for the read, Sheldon and Morgan. See any downside to trying to find the next node up, too? (barring any pressure issues, wherever they start emerging) Granted, I don't gain much in wind by doing so - if I can get closer to 2800, it's worth a mil of elevation, but only .2 mil on wind... so maybe it's not even worth trying...

Another stupid question... when tuning for seating depth, do you start shooting normal groups, or do you still shoot round robin?

 

[spife7980]

Another stupid question... when tuning for seating depth, do you start shooting normal groups, or do you still shoot round robin?

I say round robin still for the same reasons as before, to level out the conditions so that you minimize the barrel heating differences or chance of getting one group that the wind blew just right on (or rather lack of wind) while the others got gusted about. Its one of the few occasions that I advocate for socialism on; spread it around.

Unless you have enough time to let the barrel come all the way back down to temp between each group but that would seem to take forever to me.

 

[davere]

Ha ha... socialism. Thanks, Spife - I think that makes sense. And, yeah, geez, it'd take forever to get the work done if I let the barrel come back to room temp after each group.

 

[morganlamprecht]

like Spife said, for me, everything stays round robin until i pick a final load...i dont know much about 4451 cause ive never used it, but in my experience if you start getting hornady brass up over 2800 fps w/ h4350, which is similar, its not goin to last long...ive got probably 600-800 pcs of hornady brass at home with 7-10 firings on it either running 130s @ 2850 or 140s @ 2750 from 24" tubes, and i havent had to throw any pieces away yet for loose pockets

 

[davere]

if you start getting hornady brass up over 2800 fps w/ h4350, which is similar, its not goin to last long...

I'm pretty far from 2800 now, though, relatively speaking. But I hear what you're saying. There's a point of diminishing returns. When I bought my rifle, I picked up 400 rounds of Hornady 140gr ELD-M factory stuff to use until I was able to get all the stuff together to reload for it. I've since acquired 300 pieces of Lapua brass. So, I'm using the Hornady stuff as "training wheels" before I fuck up the good stuff somehow. So, if I end up wearing some Hornady stuff out in the process of playing around and learning, it's not the worst thing in the world, to me. I'm mostly focused on finding a decent load while learning good reloading practices and workflow for rifle.

ive got probably 600-800 pcs of hornady brass at home with 7-10 firings on it either running 130s @ 2850 or 140s @ 2750 from 24" tubes, and i havent had to throw any pieces away yet for loose pockets

Good to know - I'm not too far off that threshold now (roughly 50 fps slower than your 140 loads).

 

[spife7980]

I shot it normal this week. I forgot to adjust my scope based on my sighter so they are all an inch low. Realized that after my first shot for record so I was stuck shooting low. [IMG2=JSON]{"data-align":"none","data-size":"full","height":"581","width":"775","src":"http:\/\/i.imgur.com\/NROAzqR.jpg"}[/IMG2]



And the chart with the velocities from last week [IMG2=JSON]{"data-align":"none","data-size":"full","src":"http:\/\/i.imgur.com\/Xali8Kl.jpg"}[/IMG2]

 

[davere]

Looks like you started right in the middle of a node, and there's another one in the 23.0-23.2 range? Both on target and velocities?

 

[Brent1969]

Last load development session I did the following.... load 5 rounds at each charge weight. Shoot 2 shot groups through the series with the chrono on to get velocity for each charge weight. Then remove chrono and shoot the remaining 3 shots per charge weight as a regular OCW test on a separate target without the chrono attached.

Go home and plot out the velocity curve from the 2 shot series in excel... look for flat spot in velocity vs charge weight. Compare that to the OCW test looking for similar POI on target. For me there was good alignment with the velocity flat spot as well as OCW point of impact. Upper node didn't show much promise for group size but lower node shot bugholes. Went with the lower node, called it good after some final testing to confirm.

I really dig adding the velocity curve to the traditional OCW test. It's very easy to do in Excel.

Ok I am computer illiterate. How do I do this on excel??

 

[Sheldon N]

Ok I am computer illiterate. How do I do this on excel??

Make two columns side by side. First column is your charge weights, second column is the corresponding velocity (either individual for single shot or average velocity).
Highlight all the data in both columns (draw a box around them)
Go to the "Insert" tab
Select the "Scatter" chart dropdown
Select the "Scatter with smooth lines and markers" chart type

Done!

You might need to do small things like delete the "Series 1" label, or format the graph axis to be the right numbers. Just right click on anything you want to change.