OCW for new rifle

[Paqueo]

Searching for a 6.5 CM load for a new rifle started this test when 24” barrel had 130 shots.

Lapua SR primer cases once fired

N550 powder

CCI BR4

Hornady 147 grain ELD-M

COL: 2.880" (Maximum for magazine). Lands @ 2.913" (.033" Jump).

Distance to target 528 yards

first shots #1 to 5 with 39.2 grain
shots #6, 7 & 8 with 39.4 grain
Shots # 9, 10, & 11 with 39.6 grain
shots # 12, 13 & 14 with 39.8 grain


After this tested for COL

Charge of 39.4 grain
3 shots each COL: Maximum for magazine / .010" less / .020" less
Distance to target 109 yards

Any comments are appreciated.

 

[spife7980]

What made you choose such a narrow window at such a low charge weight in the first place?

To get reliable data from an ocw you need a wider spectrum of data points. Right now with this info you’re trying to navigate with a hood pulled over your eyes.

 

[Doom]

Trying to develop the load at 500yds is not going to be reliable. Too many variables come into play. Also your charge weights should span at more than 3% as nodes tend to be ~3% apart. Do your load development and seating depth at 109yds. Once you have that tight then verify by taking it out further.

Also, it appears to me that your moa is incorrect on 109 yd targets.

 

[Paqueo]

What made you choose such a narrow window at such a low charge weight in the first place?

To get reliable data from an ocw you need a wider spectrum of data points. Right now with this info you’re trying to navigate with a hood pulled over your eyes.

You are right. This wasn't the only test I did. Just posted this last one but will publish more info I got from previous tests

 

[Paqueo]

Trying to develop the load at 500yds is not going to be reliable. Too many variables come into play. Also your charge weights should span at more than 3% as nodes tend to be ~3% apart. Do your load development and seating depth at 109yds. Once you have that tight then verify by taking it out further.

Also, it appears to me that your moa is incorrect on 109 yd targets.

MOA is correct. Image is zoomed. Will post previous test. Thanks

 

[Paqueo]

Lapua SR primer cases.
CCI BR4.
Vihtavuori N550 powder
147grain ELD match
24" barrel
COL: 2.880" (Maximum for magazine). Lands @ 2.913" (.033" Jump).

1st test done @ 100 meter.
Before this test fired 10 shots with N150/140ELD_M to harm and foul the barrel.
New cases (0 firing).
Oheler 35P didnt read velocity of the 38 grain charge

Photo of the case loaded with 41.5 grain.
Cratered primer and also visible a light round ejector hole mark around the last "A" of LAPUA lettering. This case measured a slightly larger OD near the base than the other ones.
Not noticed signs on the other cases and no bolt lift increased force.

 

[Paqueo]

Then decided to do another test at 400 meter
Cases fired once. Fire-formed to chamber and sized to reduce headspace .002".
6 shots for the first charge (39.4 grain) and 3 shots for the remaining charges.
First shot the 6 with 39.4 and then the rest.
Air Temperature: 77ºF
No over pressure signs.
Oheler 35P didn't read velocities of all 40 grain charges and two of 39.4.

The guy near the target to take note of impacts got a bit confused and we had a few doubts. Anyway, below a photo of target with the groups signed with different colors.

When I did this test @ 400 meter hadn't studied properly the all data of the first test, as I did above, and probably just searched for higher velocity instead of searching in the best window.

 

[Paqueo]

Then decided to do another test @ 500 meter.
Cases fired once. Fire-formed to chamber and sized to reduce headspace .002".
Air Temperature: 63ºF
No over pressure signs.

2 shots to warm and foul the barrel (dots #1 & 2) then 3 shots each charge round Robin.
No photo of target but made this representation of POI to scale.

 

[Paqueo]

After this 3rd test I did the one I posted first.

 

[tnc]

Based on your first test, I’d explore 39.0-39.5

 

[Paqueo]

I’d explore 39.0-39.5

Thanks!
I agree they showed similar velocities but that test used brand new cases and they can slightly change the results.
Using a brand new barrel is not also too reliable. Now has some 170 rounds and should start now to speed up.