OCW, help me read this mess

[FUNCTIONAL]

Shot this today and I'm stumped. For the most part groups opened up as numbers got better and vice versa. Never seen this before.

20" bartlein
223 rem match
Standard cci primers
77smk seated 2.06" to ogive(.02" off lands)
AR Comp powder
Black hills brass bumped .002"

Almost looks like 2 ocw nodes but the numbers vs groups concern me. I get 3rds isn't a big sample but typically I see the trend carry out.

At this point I'm thinking just reshooting it but with 5rd groups and going another 2 to 3 charge weights higher. No pressure signs at all at 24.2 gr and not compressed.

 

[NORCAL50]

Graph your average velocity against powder charge and see if there is a flat spot around 23.0-23.4. If so, i'd feel even more confident in going with one of those charges because at least 1/3 of those groups has good SD/ES numbers, and the vertical point of impact shift between the three groups is miniscule.

Regarding the inverse relationship between SD/ES and group size, someone with more knowledge than I have will need to comment on that.

 

[Winny94]

Are you possibly convoluting the OCW w/ a different test? I typically dont see OCW care much about ES/SD at this point. Just looking for a consist POI at this point.
IMHO, id say your node is somehwere in the 23.3 area - the vertical variation b/w 23.0 and 23.4 look pretty solid. Starting to change at 23.6.

 

[NORCAL50]

Are you possibly convoluting the OCW w/ a different test? I typically dont see OCW care much about ES/SD at this point. Just looking for a consist POI at this point.
IMHO, id say your node is somehwere in the 23.3 area - the vertical variation b/w 23.0 and 23.4 look pretty solid. Starting to change at 23.6.

I might as well explain my method since I do OCW and I care about SD/ES. My method refers to the OCW method, which looks for very little POI shift between groups of different powder charges as well as "flatline" spots in your velocity which should correspond with the aforementioned groups that had very little POI shift (F-Class shooter Erik Cortina did a post on these flatline spots here.) My most recent data just so happens to show the flatline that showed up with my best groups. The data also shows a direct relationship between SD/ES and Group size in my case, but as apparent with the OP, does not seem to always be the case. While SD/ES are technically not numbers you need to look at for OCW, they are still helpful because in the end your chronograph is most likely gonna have less % error than the shooter and there is (usually) a direct relationship between SD/ES and group size but not always as the OP here appears to have an inverse relationship between the two.

 

[FUNCTIONAL]

Yes that's exactly what I look for as well. First time the sd/es hasn't correlated for me. I felt great shooting the groups but I think I may just shoot them again with 5 shot groups to pull a little more data. Will likely try a bit higher too since I had no pressure signs, I typically like to find the limit to know how far or close I am.

Edit: I also graph all the data as well. Since I'm going to reshoot on going to hold off on that work.

 

[Doom]

Your targets does show two nodes, 23.0 to23.2 and 23.4. to 23.6. You are looking for consistency in point of impact. Your statistics may or may not mean anything.

Typical OCW nodes in 223 are not very broad, with the nodes being only ~0.6 grs apart.

 

[Cfshooter]

I would go with 23.1 and play with seating depth using 5 shot groups and think you will have a winner.

 

[FUNCTIONAL]

Just to follow up I figured I'd post the new results. Honestly just kind of reinforces the 23.0 and 23.6 charges. No wind difference out to 700 and only .1 mil wind diff at 1000 per 5mph. Anyone see any real reason to go with one over the other? Probably only have one more range trip to test seating, zero and confirm dope before my next match so probably will pick one and roll with it.

One on bottom (4/25 date) is the latest one and is 5 shot average vs 3 on the first go around.

 

[918v]

If forced to stay in that coal range, I’d do 23.1 and adjust the coal a little to find the sweet spot.

But if you can, redo the test further away from the lands to see if you can find a broader accuracy node.

 

[FUNCTIONAL]

If forced to stay in that coal range, I’d do 23.1 and adjust the coal a little to find the sweet spot.

But if you can, redo the test further away from the lands to see if you can find a broader accuracy node.

That's to the ogive measurement (2.06") which puts me .020" off the lands. SMKs are very forgiving in seating but I've found .02 off typically gives great results. Whichever charge I pick in going to go do some seating depth tuning with, just seeing where the ocw and numbers land before that.

 

[Cfshooter]

That's to the ogive measurement (2.06") which puts me .020" off the lands. SMKs are very forgiving in seating but I've found .02 off typically gives great results. Whichever charge I pick in going to go do some seating depth tuning with, just seeing where the ocw and numbers land before that.

I would go 23.7 on low side or 24.2 on high side and play with depth a little more. I think both will do fine.

 

[918v]

He’s blowing primers at 24.4 and you’re telling him to load 24.2???

 

[Cfshooter]

He’s blowing primers at 24.4 and you’re telling him to load 24.2???

Some people like the high side, I personally go on the low, less powder lol.

 

[spife7980]

Id put a 10 of 23.4 into a group and see if it’s good enough. I bet it is

 

[FUNCTIONAL]

@918v @Cfshooter. Haha I'm usually always on the edge but this is only 75deg weather. In NC our typical match is 90+ and these are unsuppressed which i have likely will have on 90% of the time. I popped one primer at 24.2 so for me 24.0 will be my max I'm comfortable with.

Going to load up 40 at 23.4 and 40 at 23.6 test and roll with whichever gives the better numbers and group. After this match I'll play with seating depth and fine tune it....as is either will be fine for a prs match.

 

[CK1.0]

I think picking a charge weight by shooting a few groups is about the same as giving yourself a Rorschach test. Is there really something there to see or are you only seeing it because you're looking for it?

Pick a charge weight that's middle of the road, shoot groups to find your jump, then shoot a ladder over a chrono to find a flat spot, done.

 

[Mbaysinger89]

Low es/sd with bad groups sounds like seating depth. Instead of loading 40 of each load 5 at .06, .10, .14 or so and see what happens. I bet one of those would tighten up. Then load your load. Its the same test trip to the range, less loading, and a better load.