First OCW - please help me analyze

[glock24]

SH,

I was first introduced to this OCW process while reading this thread, including <span style="color: #3366FF">komboyatch's </span>informative tutorial. Thanks to all for this valuable info! My last tuning process involved too much trial and error, so I'm delighted to gain this insight.

I attempted this procedure tonight with my new 6.5x47mm Lapua, Varget powder, and Berger 130 grain VLDs. I was shooting at 100 meters in very calm conditions. I waited two minutes between shots and started with a clean barrel, fouled with three sighters. I also had the rifle in a front and rear rest.

With everything I've been reading on jumping and not jumping the Bergers, I did the OCW twice. One test was 0.010" off the lands, and the other test was 0.010" into the lands.

The chosen charge weights were relatively arbitrary and based simply on my collection of notes from other shooters.

That said, please take a look at my testing, and help me understand where I should go next. I'm conflicted about which test to optimize, and also whether or not I've included enough range in my charge weights.


<span style="font-weight: bold">First Test</span> (0.010" off the lands)

I'm not sure if 37.6 grains represents a scatter group, or whether it is really at 37.3 grains (not tested). If so, would I chose 38.0 grains and now adjust seating depth? I don't like all the vertical I'm seeing in this powder range. Is that relevant?

I'm hesitant to keep playing in the 39.0 grain range as the 39.6 grain loads produced strong ejector marks on my cases.

<span style="font-weight: bold">Second Test</span> (0.010" into the lands)

I really don't know where to begin with this one. I'm wondering if I didn't go high enough in charge weight. None of these loads showed signs of pressure.

As you can probably tell, I'm kinda lost. I'm second guessing my powder choice, bullet choice, and shooting ability. Any insight would be appreciated.

Thank you

 

[MitchAlsup]

Re: First OCW - please help me analyze

Top image 39.3 shows promise; it is sitting between two groups that are a bit big, but not out of bounds big. This suggests somewhere between 39.0 and 39.6 lies one accuracy node.

Bottom image: 38.0, 38.3 and 38.6 all show the same group scatter pattern as in the top image. Unless you are seeing ejector wipe of a stiff bolt, you might try walking up the pressure curve towards at least 39.3-ish.

So you have tow good looking groups at 38.6 and one good looking group at 39.3. You have narrowed down the search space. Suggest you survey the search space in finer charge weight increments.

 

[Powder_Burns]

Re: First OCW - please help me analyze

3 shots is too small of a sample size. You need to do 5 or 10 to get a better idea of how the loads are performing.

 

[Rich Emmons]

Re: First OCW - please help me analyze

try this

Jason Baney's ladder test

if got access to 300-500yds it can work at those ranges too.

 

[bigwheeler]

Re: First OCW - please help me analyze

37.6 through 38.3 are keeping the point of impact the most consistent. Using a
load around 38 is looks to be the most forgiving. I would try different seating depths
and maybe primers and neck tensions with that load.

 

[kombayotch]

Re: First OCW - please help me analyze

37.6 looks like the scatter group in the first, 37.3 in the second. This makes sense since seating into the lands should increase pressure and velocity. I would focus on 38.3 and 38.0.

Download OnTarget and plot the (x,y) group centers to an MS Excel chart, this will help in making things more visual. I suspect you should see the telltale "loop" when you do.

Also, post this on http://practicalrifler.6.forumer.com
Dan is good at interpretting the groups visually and might already know where the OCW load for this combination is.

 

[glock24]

Re: First OCW - please help me analyze

Thanks for the feedback folks. You've given me some good leads in which to follow up.

One follow-up question: was I wrong to do this OCW twice, both on and off the lands? Is it correct to assume the distinct pressure differences will create my accuracy nodes at different charge weights?

 

[kombayotch]

Re: First OCW - please help me analyze

Its never a waste if you learn something from it. And its another form of confirmation anyway.

Yes, you would most certainly see a slight difference in charge weights for the nodes if you're seating into the lands vs. out of them. There isn't much of a difference if you're moving stuff around away from the lands, but one you get close to them or into them, you do start seeing a difference.

 

[lawrence97]

Re: First OCW - please help me analyze

I would definitely try to stretch it out to at least 200 yds. for the test to have significance and it will be easier to identify what works.

Also, before playing with seating depths, I would figure out a good powder charge and then fine tune it with very minor seating depth adjustments. It seems as if you are playing with too many variables which can be a data overload...

 

[doc76251]

Re: First OCW - please help me analyze

You have consistent "split groups". Which is indicative of either a heated tube (not likely with 2 min between shots) or you are getting excited and not doing things the same.

You may find some benefit to dialing the scope up 3 or 4 minutes and concentrating on where you are aiming vs. having the target change in appearance with boolet holes in it.

FWIW I would look at the 38.0 - 38.6 range.

Don't shoot where you are aiming! This test is all about group location. You will need to ensure that your target is plumb and level to make ANY sense out of it though.

Cheers,

Doc

 

[glock24]

Re: First OCW - please help me analyze

Thanks again guys. I think I'm going to try this experiment again per <span style="color: #3366FF">Doc's</span> suggestion because I know I was guilty of "getting excited". I'm going to move my POI away from my POA and not get so uptight about group size during the experiment.

I also plotted the x,y centers per <span style="color: #3366FF">komboyatch's</span> suggestion. Remind me again what the loop means?

 

[kombayotch]

Re: First OCW - please help me analyze

I haven't done an extensive study, but from doing a lot of these plots, I notice that around the node you tend to see the curve do a loop. It is different than a sudden change in in direction and there are usually 3 points that are fairly close together. But sometimes it is only formed by 2 points.

Did you record any velocities while doing this? If you follow my example, you will notice the Hornady and Lapua brass results formed similarly shaped curves. And that the points on those curves had virtually the same velocities for similar locations on the curves. There are some similarities in the shape of your two curves. And the points seem to have a pretty consistent offset... around 1.0 gr. less for the "on the lands" puts the points into a similar pattern.

As Doc points out, if your groups are being biased by flinching or poor technique, the results may be harder to interpret. I bet those curves would look very close and velocities would be close for similar points otherwise.

 

[glock24]

Re: First OCW - please help me analyze

Okay guys, I went back to the range today with some good advice. I moved my POI off the target and concentrated on the bullseye and not the bullet holes. I feel like these groups are a lot more rifle and and a lot less shooter.

I also decided to try H4350 as it is a bit slower than Varget. Dan's OCW procedure recommends using the slowest powder first.

Below are my results. And just for <span style="color: #3366FF">kombayotch, </span> I also plotted the (x,y) centers. Boy is it a mess!

So what you think? I really like the velocity of the 42.0 group, but the 40.3 group is probably my OCW. Should I stick with H4350, or retest the Varget?

 

[doc76251]

Re: First OCW - please help me analyze

That we can work with! Well done.

Having done these once or twice I would be looking VERY hard at 41.0gr and play with your seating depth. OCW is useful only if you can pull a charge that is in the middle of a "flat spot" in group location. Between 40.3 and 41.6 there is very little group location shift.

Contrary to popular opinion the roundness or the tightness of the groups have little to nothing to do with OCW. You get that by tweeking the seating depth.

Oh one other thing an OCW load will give you is temperature insensitivity. If your rounds land in the same place + / - .5gr how much velocity up and down is that? Does that velocity spread cover you velocity changes due to temperature? Most times.

Nice shooting!

Cheers,

Doc

 

[kombayotch]

Re: First OCW - please help me analyze

The first 3 groups for a nice tight loop. There is definitely a node 40.0 and I think you may have another at 40.0-42.3+

 

[bigwheeler]

Re: First OCW - please help me analyze


42 would be the load for me. The poi on either side is the same and it has the
speed you want. I agree that 40.3 has a great group as does the 40 but the poi
drifts right a bit with the 40.6 meaning your sweet spot goes down to the 39.6.

 

[JLM]

Re: First OCW - please help me analyze

I've been dabbling with the OCW method.

How do you make the chart above and even more important how do your interpret the results from the chart?

 

[glock24]

Re: First OCW - please help me analyze

I'm learning this too, so bear with me . . .

The chart comes from plotting (MS Excel, scatter plot) the horizontal and vertical offsets between the POI and the center of the grouping of bullets.

The easiest way to calculate these offsets is by using a sweet little software program (free) called OnTarget. This software lets you input digital images of your targets, and with a little input from you, it calculates all the information.

From what I know, the point of the chart is find the section in the loop that "flattens out" or has the least spread. This is basically the same as analyzing the targets visually and looking for the OCW.

I posted my targets over on Dan Newberry's website. As one of the pioneers of OCW, he is very good a visual analysis. He's also against using the charting method, although I kinda like it.

http://practicalrifler.6.forumer.com/viewtopic.php?t=947

 

[Greg Langelius *]

Re: First OCW - please help me analyze

Whether you group is 3 or 5, or even 10 shots, no single group is indicative of anything but that one group, and is only marginally applicable to anything else.

What is important is each shot, its deviation from a common Point Of Impact, and of that point from a common Point Of Aim.

I shoot individual shots at targets of my own design at 100yd. They consist of 4 columns of 5 rows, yellow 1/2" dots with bold black borders.

Those numbers are just personal preferences, the important thing is that each shot has a Point Of Aim, and a deviation from it.

As I shoot, I keep an identical target alongside me at the bench, and annotate that target with the POI as well as anything pertinent about that shot, for each shot, as the shot is completed. This allows me to see each shot in its own context, and to compare them each and all at a glance, with no doubt or confusion about the influences involved.

I will shoot fairly large quantities of shots for each increment, and make some arbitrary decisions about how many increments I use; keeping them as limited as a SWAG can determine. Sometimes, no increment will offer itself as ideal, but nearly always the first set of increments will either point me in a likely direction, or confirm that good enough, if not ideal, accuracy will be found within the incremental limits I have chosen to test.

I'm not shooting BR, I have no need for the bestest possible load recipe, I simply want something I can shoot and not feel too shabby about. But very often, by the second or third round of tests, I'm at or in the ballpark of something pretty close to ideal anyway.

I try to keep the load fabrication methods simple.

It's maybe a no brainer, but seeking loads that require extra operations and efforts would appear to be counterproductive to my goals. Restated, if I wanted a simple life, why would I seek it by doing complex things? Maybe, if what I'm doing can only be accomplished by doing the complex; then maybe, just maybe, I'm approaching the problem from the wrong direction, eh?

Life is a hard as you choose to make it; and if it's harder than you think is reasonable, then by your own definitions, you're doing it wrong.

One final thought. Large increment groups make for a lot of component expenditure. Some times are better than others for doing this, and at times like these, when components are rarer and dearer, it may pay to shoot with what you have that works, rather than branching off into the fields of experimentation. Some things can wait.

Greg

 

[JLM]

Re: First OCW - please help me analyze

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: glock24</div><div class="ubbcode-body">I'm learning this too, so bear with me . . .

The chart comes from plotting (MS Excel, scatter plot) the horizontal and vertical offsets between the POI and the center of the grouping of bullets.

The easiest way to calculate these offsets is by using a sweet little software program (free) called OnTarget. This software lets you input digital images of your targets, and with a little input from you, it calculates all the information.

From what I know, the point of the chart is find the section in the loop that "flattens out" or has the least spread. This is basically the same as analyzing the targets visually and looking for the OCW.

I posted my targets over on Dan Newberry's website. As one of the pioneers of OCW, he is very good a visual analysis. He's also against using the charting method, although I kinda like it.

http://practicalrifler.6.forumer.com/viewtopic.php?t=947 </div></div>

Actually I've been using OnTarget to make the plots I just suck at Excel mostly, need to figure out how to make the thing in Excel so I can see it. Thanks

 

[SuperXJeff]

Re: First OCW - please help me analyze

Great post Greg ( elder fart). I look at getting the most for the least and sometimes it works. I know this site is all about precision but it sounds like this is a pretty new gun/ Can he really come up with the best load this soon or does his rifle need a little more seasoning? It's one old shooters opinion but with so many groups with two bullet holes touching it would seem a little hasty to have any direction just yet, 40, 40.3 and 42 with the 4350 are pretty close and yet a little far apart as far as charge weight goes. If it was me I would do what you are doing but start trying diffrent primers. In early load development I like to see big swings that indicate a real direction to head before I settle on a charge weight that varys but less then two grains that produce groups that are so very close. I don't know what you goal is with this load( Accuracy I know!) but as it stands the gun appears to be a shooter. Good luck! Jeff

 

[glock24]

Re: First OCW - please help me analyze

Okay guys, one more question if you don't mind . . .

I took Dan Newberry's advice on OCW recommendations for both my Varget (38.0 grains) and H4350 (40.0 grains) test runs. I then conducted a round robin with seating depth.

I decided to go with the following;

0.010" into the lands
0.005" into the lands
0.005" off the lands

Is this sufficient, or should I extend the range of my testing?

Below are my results. I really, really like the Varget powder because it gives me a solid 100 fps more than the H4350 (2850 fps vs. 2750 fps). As you can see however, the H4350 shot the best group.

So now what? Does this mean that H4350 is preferred, or should I not give up on Varget so soon? My next steps will include lots of 5-shot groups at longer ranges. I'd like to pick one powder and move forward.

What do you think?

<span style="color: #3333FF"><span style="font-weight: bold">Varget</span></span>

<span style="color: #3333FF"><span style="font-weight: bold">H4350</span> </span>

 

[kombayotch]

Re: First OCW - please help me analyze

You can make adjustments when you're away from the lands without affecting things a great deal and sometimes small ones when you're in the lands. But, you can't mix the two without adjusting your charge weight.

Unfortunately, you are re-tuning your loads by seating them in and out of the lands. It can be seen clearly by their change in point of impact and was also noticeable in the analysis of your two Varget tests above. The +/- 0.005" is probably, for all intents and purposes, the same.

 

[glock24]

Re: First OCW - please help me analyze

Dang it!

Well, I have OCW numbers for both powders with the bullet into the lands. How far in and out should I consider testing the seating depth, assuming I never leave the lands?

Do you think there is any reason I should consider retesting off the lands with these bullets? I know anything is possible, but the VLDs seem to like being seated into the rifling.

 

[kombayotch]

Re: First OCW - please help me analyze

Generally, you always want to be pulling things back since it reduces pressure (until you start pushing the bullet deep into the case a lot).

For out of the lands, start with your 0.005" off and pull it back in 0.005 or 0.010" increments. For into the lands, take your deepest depth into the lands and pull it back in 0.002" increments (it's more sensitive in the lands). I prefer being out of the lands because you don't have to re-adjust as often as the throat erodes. Your Varget load did as well 0.010" out as it did 0.010" in...

When adjusting the seating depth, the point of impact should stay the same, as should velocities. Do this testing over a chronograph. When you start seeing noticeable changes in velocity in conuction with your seating depth changes, it means things are starting to re-tune. If the velocities are changing, so are the pressures and thus, the barrel times are changing too.