Help! Need help deciphering OCW results

[hkfan45]

Just got back from the range. Rifle is a 24" bolt.
Lapua 308 cases
BR2 primers
175 SMK seated 0.015 off lands
Varget powder

I did a 3-shot OCW test from 43.7gr - 45.2gr of Varget in 0.3gr increments (1st picture).

Then, I shot a few 5-shot groups of 42.9, 43.0, and 43.1gr of Varget (2nd picture) because I had some success with this before. However, I'd like help narrowing down a charge weight that gives me some higher velocity (hence the 43.7-45.2 range). Can anyone make heads or tails as to which powder amount I should investigate further?

BTW, the pictures take a bit to load. Please be patient and thanks for helping this newbie. If the pictures wont load, please post here or PM me.

 

[Temp9]

Were these shot "round robin" style (is that the right phrase?). That's very important in OCW. Your 43.7-44.3gr loads have little POI shift. I'd do some accuracy testing with those three loads.

 

[hkfan45]

They were not shot round robin. You got me. I wanted to shoot three successive shots to measure SD and didn't realize it would have such an impact. Looks like I should reshoot these then.

 

[hkfan45]

What I'm still puzzled by is my 45.2 load. All 3 shots had the exact same speed, 2750 fps, and yet the group showed vertical stringing. User error?

 

[Twoboxer]

The POI of your 44.6 and 44.9 groups are virtually identical. And had to look hard to find 3 holes. I'd split the difference and test 44.8 gr. If that load confirms as good, with near the same POI (as it should), you have a nice wide range allowing possible slight variations in load yet hitting the same POI.

Nice shooting.

 

[Dacam]

I truly don't understand why so many people do an OCW load test only to try to modify it to what they think is correct. You should read up on the concept of the optimal charge weight testing and do it again. The whole point of shooting the test in a round robin format is to spread the error factor through the "all" groups fired.
A lot of rifles that shoot 175g will find a load at around 43.0 Varget with a high node at around 45g.

 

[oldfatguy]

They were not shot round robin. You got me. I wanted to shoot three successive shots to measure SD and didn't realize it would have such an impact. Looks like I should reshoot these then.

Yes you need to load & shoot again. The "round robin" thing is very important for OCW testing. Otherwise you have a collection of three shot groups.

OFG

 

[mdmp5]

What I'm still puzzled by is my 45.2 load. All 3 shots had the exact same speed, 2750 fps, and yet the group showed vertical stringing. User error?

It may be a flinch, parallax error, aiming error, etc. However, even if your shooting form is not to blame, and the velocities are identical, you can still be outside of the node, which is what you are searching for in the first place.

 

[hkfan45]

I still am uncertain on how to proceed. Rerun the ocw using the round Robin approach? Or focus on the charges that seem to be producing the best groups? (I. E. 43.1 and 44)

Ive wasted so many rounds already trying to find the right load, I guess I'm looking for a next step that involves the least amount of rounds to identify the best node. I do not have access right now to anything else longer than 200 yards, so I think the ladder is out.

Prior to trying this one test, I loaded five shot groups on the lower end of the charge scale and just looked for the best groups. I liked that strategy because it was more obvious, but the ocd in me wants to make sure I really am picking the best load.

 

[SEMO Shooter]

OCW is not about finding one charge weight that groups well. It is about finding a range of charge weight that impact in the same vertical plane and not scatter. Find that range or node, then fine tune the load with minor changes in charge weight, and do final fine tuning by adjusting seating depth. It really doesn't take many rounds to do the test right.

 

[hkfan45]

Aside from failing to use the round Robin, was the test conducted correctly? Using 0.3gr increments correct, and should I also include the lower charges (42.9-43.7) in a rerun of the ocw test?

 

[jsthntn247]

Your 44.9 group is your OCW because 44.6 and 45.2 hit at the same POI. Start at .030 off lands and work to a .010 jam in .005 increments and you will be done.

 

[Twoboxer]

I still am uncertain on how to proceed. Rerun the ocw using the round Robin approach? Or focus on the charges that seem to be producing the best groups? (I. E. 43.1 and 44)

Ive wasted so many rounds already trying to find the right load, I guess I'm looking for a next step that involves the least amount of rounds to identify the best node. I do not have access right now to anything else longer than 200 yards, so I think the ladder is out.

Prior to trying this one test, I loaded five shot groups on the lower end of the charge scale and just looked for the best groups. I liked that strategy because it was more obvious, but the ocd in me wants to make sure I really am picking the best load.

- Based on your post here, I'd strongly suggest re-reading the purpose and methodology of the OCW test.

- You are looking for the center (ideally) of a "node" where small variations in powder charge/pressure do not materially change the POI. This node should also be as far away as practical from nodes where harmonics cause the groups to open up. Your targets show that node is in the area of 44.6gr to 44.9gr

- Your failure to shoot round robin may or may not have had a material impact on your test. If you'd like to repeat the test, feel free. If not, repeat 44.6 & 44.9 to confirm results. If they shoot the same as you original test, then either pick one of those, or a charge in the middle, eg, 44.8gr.

 

[308Gunner]

+1 with Twoboxer 44.8

 

[bruddah]

Good thread.