Analyze this OCW target

J

Jason280

Sergeant
Full Member
Minuteman
Dec 18, 2005
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GA
#1
Finally put together an OCW load for my 24" Savage 10FP .308, and was able to try it out today. Gun is a Savage 10FP in a Choate stock, with a Falcon Menace 4-14x44FFP scope. Distance was 200 yards, and I waited a minimum of 30 seconds between each shot. I used BHA Match cases trimmed to 2.005", with 168gr Hornady BTHP to COL of 2.800". Primers were CCI BR, with charge weights going from 41.1-43.5gr of H4895. Here are the velocities:
41.1 2569fps
41.3 2569
41.5 2583
41.7 2614
41.9 2624
42.1 2645
42.3 <span style="font-weight: bold">2629</span>
42.5 2661
42.7 2699
42.9 2732
43.1 <span style="font-weight: bold">2699</span>
43.3 2743
43.5 2726

Not sure what happened to the velocities in bold...

Here's the target, with a couple dimes for reference:

Target001.jpg

Target003.jpg


Based on the target and velocities, how would you evaluate these results? Shots #5, 6, & 7 are within 1.25", with #7 expanding the group (which also had one of the out of place velocities of 2629fps). #10 & 11 are similar, with #12 opening the group to 1.25".

Thanks!
 
#2
Re: Analyze this OCW target

I would say you've found 2 nodes. The first is at shots 5 and 6 and the second is at 10 and 11. And between the two I would say 10 and 11 is your more accurate OCW load. Even though the velocity of shot 11 was out of place with the rest of them, the POI is still right close to the central POI. So, 43.0gr is probably your OCW charge based on this target. But I would be surprised if you tried this load and it grouped as well as you expected. What you have shot is closer to a ladder test and not an OCW development target although your findings might be same if you did try an OCW target sequence. Ladder tests and OCW targets get a good starting point but I never had repeatable success with either method. YMMV. Post back and let us know how it shoots with what you try.
 
#3
Re: Analyze this OCW target

That's a ladder test... you really need to run it in 0.1 gr. increments to get reliable info out of it. 0.3gr. is too big of a jump when you're only firing one round of each. A little over 2600 fps. is where one of the nodes is though, I believe. The second one should be a bit higher than 2700 though, if I recall correctly.

This is OCW: http://www.clik.to/optimalchargeweight
Dan's forum is here: http://practicalrifler.6.forumer.com/viewforum.php?f=4

I would bet you could find other people's OCW tests using the same set of components (or similar) to what you're using. Winchester brass has a similar case capacity to BHA Match.



<span style="font-weight: bold">Here's a little tutorial from one of my OCW tests:</span>

I loaded 20 rounds in Lapua brass (I really did 35, but forget about the second target for this example). The first five rounds were just fowler shots that were also used to get me in proximity to the target. They were the middle charge. I fired those to foul the bore and then adjusted my zero to get the groups close to the bullseye, but not on it (didn't want to obscure it). From this point on, I NEVER touched the turrets.

Now, I have 15 rounds left. 3x 44.1, 3x 44.4, 3x 44.7, 3x 45.0 and 3x 45.3

I start shooting those at the target in a round robin sequence. This means I shot a 44.1 at tg#1, then a 44.4 at tg#2... then a 45.3 at tg#5 (one on each target). Then I start over at 44.1 on tg#1 again and repeat the sequence twice more. I always let the barrel cool between each and every round. I'm NOT shooting all the rounds for each charge all together. This is important. This way things like fouling and wind are distributed to each group and do not bias any one individual group.

I get this target:
190smk_rl17_l1.jpg

Now, I examine the Target. I look for the scatter group. I see it at 44.4 gr. There should be 3 groups after it (in sequence) that have the center point in about the same location. And there they are: 44.7, 45.0, 45.3. I choose 45.0 as the OCW.

When I plot the center points (Off H: x" V: y") on a chart (to make them more visual), I get this, which also includes higher charge weights that I left out of this example:

190SMK_RL17_Lapua_Chart.jpg

Notice the loop these charges from and the associated velocities.

Now, just for fun (and because I have different brands of brass) I ran the numbers in Quickload and figured out what charges gave the same velocities in Hornady brass. I do the OCW sequence again and get this:

190smk_rl17_h1.jpg

See the scatter group at 45.2. Here the OCW is at 45.8. Makes sense, Hornady brass has a larger internal capacity. My center point plot looks like this:

190SMK_RL17_Hornady_Chart.jpg

Notice the loop is formed by the same velocities?

If I put them together on the same chart:

Combined.jpg

They land in virtually the same location. I've found it to be not only repeatable, but repeatable with different brands brass when internal volume is compensated for. However, these days I just use my Pressure Trace system to tune a load. It shows me the barrel exit time relative to the Optimum Barrel Time (OBT) node. It works very well,

Now, if you aren't using a temperature stable powder, the load will get un-tuned when the temperature changes a lot. Which is why I switched to Varget. H4895 is a good choice.

 
#4
Re: Analyze this OCW target

How would you then decide what would shoot better at longer distances say 400, 600, or 1000 ?? Or what is the easiest most predictable way ?

Up close and you only have to worry mostly about speeds and group sizing due to loads--- but get out to 600 yards and try this and wind will make it impossible.

I did a similar workup with varget for 175smk and 155 scenars, but the accuracy points of charge weight at 100 yards opened up at 200. From 1/4moa to 3/4moa. I tried to very the charge up or down from the happy 100yd charge weight but just couldn't dial it in as nice. Felt like 400 yards or more would be impossible. Should I just load up 5 rounds at each charge weight and just go for it the way you did except do it 600yds and make guestimates with wind ??
 
#5
Re: Analyze this OCW target

You need to do the initial up close work before testing at any distance. The point of the OCW is to find the charge weight(s) that cause the bullet to leave the barrel when there is the least amount of disturbance at the muzzle (the Optimum Barrel Time - OBT), it isn't to instantaneously give you the best load that works at all distances. It won't tell you how well a bullet flies at 400, 600 or 1000 yards. Only testing at those distances will do that.

After you have the OCW, you would then play with seating depth to find the best distance in relation to the lands. Then you would examine your velocities. At longer distances, consistency in velocity is a requirement. If you aren't getting consistent velocities, first look at your brass. If its not uniform or has problems, you will not get consistent velocities (is neck tension consistent?, does it need to be annealed? do you have donuts?... debug it). If the brass is good, and you still don't have consistent velocities, try changing the primer and adjusting the charge to the same velocity you found the OCW at.

Only once I've gotten the SD down and shrunk the groups as much as I can, do I go on to testing at distance. The groups don't have to be smaller than a dime at 100 yards. Some bullets don't stabilize fully at 100 yards. You still need to do your testing at longer distances. But, if you haven't addressed the basics, you aren't giving the bullet it's best chance at succeeding.

I've noticed that many popular loads people talk about happen to be on or really close to OBT nodes. With the Pressure Trace system I can work up loads in just a few rounds. And, I don't need to go through the exercise above to find the OBT nodes, it tells me all I need to know to find them. In the area of the load between starting and maximum charge weights, the relationship between powder charge weight and velocity/pressure/barrel exit time is pretty linear. After firing a few groups at a few incremental charge weights, I can interpolate the results to find the value I want for any of these.
 
#6
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kombayotch</div><div class="ubbcode-body"> It won't tell you how well a bullet flies at 400, 600 or 1000 yards. Only testing at those distances will do that.

Only once I've gotten the SD down and shrunk the groups as much as I can, do I go on to testing at distance. The

You still need to do your testing at longer distances. </div></div>

What do you recommend for testing procedures ? Just shooting for groups ? and if this is the case how do I tighten up the group based on my problem below ? I tried to vary the powder charge and bullet seating depth and couldn't shrink the group.

155 Scenars, 46.3 varget, 210M, new lapua brass, 25" shilen select blueprinted - My SD's are single digit and ES generally in the teens, no pressure signs, speeds are good. Will shoot less than 1/2" at 100-- same load at 200 spreads out to 1 1/2" group-- same SD ES- just aiming at a farther target. Tried working the powder amount and couldn't tighten it up ? ? Shot 3 to 4" groups at 350yds the other day and 4 and 5" at 600yds on friday (vertical stringing and round groups- wind wasn't too bad) ??
 
#7
Re: Analyze this OCW target

.1 gr increments? For initial testing? Isn't that a bit little?

I can see .1 gr when fine tuning but for initial testing that's a bit fine in my opinion.

I see the node as 5,6,and 7 I would shoot those 3 charges and I bet they are all together. I think #7 was a loading mistake. If you go straight up the target it is in the area of 5 and 6. If they are in fact all together after you shoot those 3 charge weights, go with your #6 charge weight. Why? because if you are off by a gr. in either direction when you drop charges you are still in the node your rifle likes.

I do prefer the round robin over the OCW for testing.

Just my .02
 
#8
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">155 Scenars, 46.3 varget, 210M, new lapua brass, 25" shilen select blueprinted - My SD's are single digit and ES generally in the teens, no pressure signs, speeds are good. Will shoot less than 1/2" at 100-- same load at 200 spreads out to 1 1/2" group-- same SD ES- just aiming at a farther target. Tried working the powder amount and couldn't tighten it up ? ? Shot 3 to 4" groups at 350yds the other day and 4 and 5" at 600yds on friday (vertical stringing and round groups- wind wasn't too bad) ??</div></div>

Was your objective on your scope adjusted correctly? Sounds like parallax was off to open that much at 200 if you numbers are that good.

Ideally the single digit SD is wanted. ES should be close to 10.

Use that load but try a different primer. I had my 1K br rifle dialed in like that and was using Fed210's a ragged hole at 100. Good but not what it should have been. I switched to CCI BR 2's and they shot high .1's and low .2's day in and day out when I was on my game. I had a buddy who's rifle was just the opposite. REal good with BR 2's but switching to 210's was even better.
 
#9
Re: Analyze this OCW target

Did you sort brass by weight? Bullets by weight and lenght of bearing surface? Did you check run out on a concentricity gage? Was there any wind / mirage?

Im not picking apart your testing, just wondering if you were getting all the ts crossed.

Wedas question about parallax is very valid.
 
#10
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SP308</div><div class="ubbcode-body">
155 Scenars, 46.3 varget, 210M, new lapua brass, 25" shilen select blueprinted - My SD's are single digit and ES generally in the teens, no pressure signs, speeds are good. Will shoot less than 1/2" at 100-- same load at 200 spreads out to 1 1/2" group-- same SD ES- just aiming at a farther target. Tried working the powder amount and couldn't tighten it up ? ? Shot 3 to 4" groups at 350yds the other day and 4 and 5" at 600yds on friday (vertical stringing and round groups- wind wasn't too bad) ?? </div></div>

Testing at long range won't make something shoot good, it will tell whether or not it does. Perhaps your test is telling you that the Scenar isn't going to perform up to your expectations at those ranges. I would try a different bullet, the 175 SMK for example, and compare.

Other than that:
-Ensure that your barrel is free of access copper and of the carbon ring.
-Try different brass. Not necessarily a different brands, but a different batch... maybe new cases. This will tell you if there is a problem in the cases that you maybe aren't seeing.
-Are you jamming the Scenar into the lands? They shot best when jammed into the lands 0.015-0.020" in my rifle.
 
#11
Re: Analyze this OCW target

I thought Scenars too shot well whislt being jammed and I have a load that proves that.

However, on friday I was doing some retesting and found they also love to be jumped .010-.012 My ES went from 11 to 5

Changing up the brass isn't ever a bad idea while testing to just make sure.
 
#12
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Weda'</div><div class="ubbcode-body">.1 gr increments? For initial testing? Isn't that a bit little?

I can see .1 gr when fine tuning but for initial testing that's a bit fine in my opinion.

...

I do prefer the round robin over the OCW for testing.
</div></div>


I think you're comfusing OCW with the Audette Ladder. If you're doing OCW, you're automatically doing a round robin. That's a critical part of the OCW methodology. The OP was doing an Audette Ladder, not OCW. The example I posted (with round robin in it) was OCW.

The finer increment is necessary if you want redundancy in the Audette Ladder since you're only firing one round at each charge weight. With 0.3gr. increments, firing only one round, its easy to march right over the node and miss it. If you pull a shot a bit or even just because of variations in bullet impact that occurs within groups, you may not get a cluster. There's insufficient information and too much room for variation for the test to be repeatable otherwise.

The "OCW vs. Ladder" tab on Dan's page also explains other shortcomings of the ladder method:
http://www.clik.to/optimalchargeweight
 
#13
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">With 0.3gr. increments, firing only one round, its easy to march right over the node and miss it. If you pull a shot a bit or even just because of variations in bullet impact that occurs within groups, you may not get a cluster.</div></div>

Do you really want to work with a powder that has such a narrow tune window?
 
#14
Re: Analyze this OCW target

Sorry, I'm not buying the .1 gr increment thing in .308 size cases or larger. Maybe 6br, 6ppc etc.

.1 gr is often a kernel or 2 of the powders used in .308 size cases and larger.

.2gr is possibly the smallest I would ever consider until fine tuning.
 
#15
Re: Analyze this OCW target

No, I really don't want to work loads that narrow, which is why I use OCW and not the Ladder method. The ladder is VERY tedious if you want to do it right.

Only 2 or 3 of the charges in 0.3gr. increments will fall on the node (in 308 Win.). If you're only firing one round for each weight, its very easy to miss it. Which is why you fire three with OCW. You fire them in the round robin sequence so that no charge weight gets biased by wind and/or barrel fouling.

I'm not advocating 0.1 gr. for OCW, just the ladder.
 
#17
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pgs</div><div class="ubbcode-body">Did you sort brass by weight? Bullets by weight and lenght of bearing surface? Did you check run out on a concentricity gage? Was there any wind / mirage?

Im not picking apart your testing, just wondering if you were getting all the ts crossed.

Wedas question about parallax is very valid. </div></div>

Well, I think the object of finding the Optimal Charge Weight (OCW) is to find the combination of powder charge and bullet that is least sensitive to minor variations in the other variables: case brands, primer brands, minor charge weight variations, primer lots etc. Once you've got it you don't have to be so particular about these things and you will still have a load that is accurate.
 
#18
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Sorry, I'm not buying the .1 gr increment thing in .308 size cases or larger. Maybe 6br, 6ppc etc.</div></div>

I wouldn't touch a load that has .1gr sensitivity in a 6PPC.
 
#20
Re: Analyze this OCW target

The resolution you run the test at has absolutely nothing to do with how sensitive your load will be. The whole point of both tests (OCW and Ladder) is to find a range of charge weights where the load isn't sensitive to changes in charge weight (or other variations that have the same effect). The 0.1gr. in the ladder test is used to find that range. If you pick the charge weight right at the center of it, your load will be less sensitive to a change in powder weight (or other variations) than a load that is not at the center of the node.
 
#21
Re: Analyze this OCW target

I think attention also has to be paid to the procedure used in testing.

Case in point, after a match a couple of weeks ago I was comparing notes with another F-Class competitor. He told me he had a problem with shots dropping out of the 10 ring into the 9. I asked him what his results shot over a chronograph looked like. He said he shot a few rounds to get his velocity numbers but never looked at his S.D. or spread. I told him to redo his test with a 10 shot string. I checked with Quicktarget, 25fps velocity change amounted to over 2" drop at 600 yards. We shot another match yesterday where he told me his findings before the match. He repeated his test and found the issue with his loads. His loads looked good until until he had to wait for a good wind condition to shoot in. The heat soaked round showed a 49fps DECREASE??? in velocity ( almost 5" additional drop @ 600 yards). He repeated the test to confirm results. I told him he let the round heat soak waiting a few minutes for the wind to change. He said the barrel was warm but not hot. I explained to him that the ammo was the outside temp, around 40 degrees. If a barrel is "warm" it may be around 80~90 degrees, thats a 40 to 50 degree temp change. I told him that I don't chamber a round while waiting for a wind shift..........................


Me and my big mouth, he beat me by a point.
smirk.gif
 
#22
Re: Analyze this OCW target

Thanks for the information. Some have mentioned a 0.3gr jump, which is not what I used. I went from 41.1-43.5gr in 0.2gr increments, and I realize now I confused the ladder test with the OCW method. I think I'm going to try loading 10rds of 42.1gr and 10rds of 43.1, and see how they shoot at 100 yards.

I intitially wanted to use Varget, but have not been able to find any locally. H4895 is what my .223 likes, and I have close to 6lbs of it to use. With 24.5g H4895 over a 75gr BTHP, my 10FP .223 is shooting 1" groups at 200 yards. Hopefully, I can get my .308 to do the same...
 
#23
Re: Analyze this OCW target

This is all very good stuff. When I read this I go get my legal file of targets and re anylize them. Even though I didn't know what it was, in the past I did the OCW sometimes round robin and sometimes a Quasi OCW shot sequential. The newer workups are all round robin.

It's pretty cool to see the scatter in targets I fired 3 and 4 years ago and didn't make sense of the patterns then.....wondering if it was me or the equipment.

Ejacation is a good thing.
 
#24
Re: Analyze this OCW target

I am not a harmonics denier, but when I do a work up and record all the group sizes, I imagine I have found some sweet spots.
Then if I try to replicate the process on the next trip to the range, the sweet spots are at different powder charges. That is with the same rifle, bullets, powder, brass, primers, OAL, same rest, same range.

I am, again, not denying barrel harmonics, but I am saying that, like neck turning, the benefits are too subtle for my level of shooting.

I must be dealing with recoil differently, gusts of wind, or some out of control variable that drowns out barrel harmonics down in the noise.

What I am finding in my 20 year accuracy quest, is that once a quality barrel, concentric ammo, and no wind come together, the ratio of bullet weight to rifle weight is proportional to group size. That is why benchrest has weight classes.

 
#25
Re: Analyze this OCW target

I agree the 5+6 and then 10+11 are the accuracy node approximate weights. I tend to suspect that 11 is nearer an accuracy range simply because it has a strange velocity and yet still printed well.

If are seeing no pressure signs run a batch spanning 10 and 11 at as fine a charge weight increment as you can measure, and shoot 5-shot groups. If you find an accurate load in that group concentrate on developing it. Otherwise, drop back to the 56 and run a batch spanning that range (as above).
 
#26
Re: Analyze this OCW target

I usually call up a friend with Quickload and have him run some numbers for my components. Then I look at my OBT chart and round robin 5 shots at .2gr increments that fall above and below the OBT nodes for my barrel length.
Once I find the load that runs well, an interesting thing is that it runs pretty well in all my 308's (something that Federal gets its FGMM to do).......
The third rifle I've used the same load with just dropped me 2.090" and 2.294" groups at 500 and 600yds respectively, and I just throw my charges checking every tenth or so. No neck turning or other crazy prep.
This is with my 308 running 168's. I seat them the same ogive length as FGMM.

I'm going to try out 175SMK's when I run out of 168's.
 
#27
Re: Analyze this OCW target

Ok, so can anyone give me some advice using this OCW method when trying to develop a 600yd load for a service rifle. It seems like this test would work best using a scoped rifle because your POA is so much more precise.
 
#28
Re: Analyze this OCW target

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">I usually call up a friend with Quickload and have him run some numbers for my components. Then I look at my OBT chart and round robin 5 shots at .2gr increments that fall above and below the OBT nodes for my barrel length.
Once I find the load that runs well, an interesting thing is that it runs pretty well in all my 308's (something that Federal gets its FGMM to do).......
The third rifle I've used the same load with just dropped me 2.090" and 2.294" groups at 500 and 600yds respectively, and I just throw my charges checking every tenth or so. No neck turning or other crazy prep.
This is with my 308 running 168's. I seat them the same ogive length as FGMM.

I'm going to try out 175SMK's when I run out of 168's. </div></div>

Optimium Barrel time Paper http://www.the-long-family.com/optimal%20barrel%20time.htm
 
#29
Re: Analyze this OCW target

Bro
u wanna ID MAX load for your gun, work back from that.

I find most loads are within 1.5gr of max

Load until u see ejector wipe or sticking bolt, back off .3 thats your MAX load for combo

From baseline (.3 under MAX) work back 5-6 .3gr increments

Shoot round robin @ 200/300 done deal
 
#30
Re: Analyze this OCW target

Not to drag up an old thread but I've just finished reading this. All I can say is the more I learn the more I realize how little I know! Some great info, thanks to all for adding to my continued education!

Where can I find the group measuring software?

Thanks,
Rath
 
#35
Re: Analyze this OCW target

I just checked the link and was amazed at the science involved in the reloading process. Even though I have a load that shoots a 5 shot ragged hole, I want to try this OCW process, just for the experience.

This web continues to impress me on the high level of tech knowledge the members share here.
 
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