Selecting powder nodes from chronograph/SDs/flatspots - What am I doing wrong?

[MikeMcCasland]

Hey Guys,

This should be a fun thread.

I want to preface this by saying, I don't have a problem finding good shooting loads; generally speaking I can come to the line with a competitive rifle. I will usually perform load dev at 300 yards, and look for flat spots in vertical dispersion, then tune depth. If it shoots well for me at 300, it'll typically perform quite well out to 1k.

That said, I've been on a quest to become more efficient in load selection, and I've seen lots of folks on here (not just internet high-masters, but known/accomplished shooters) talk about only using a chronograph to identify their powder charges/primer combos.

I'm familiar with the general theory of how to do it. Basically identify a rough range of where you expect the rifle to tune in (within 1-1.5gr), then load up maybe ~3 rounds at each powder charge in .1 or .2gr increments (depending on the cartridge), qty 3 for each primer you want to test. From there you can identify flat spots in velocity along with low SDs. In theory that should identify your ideal charge node.

Example: .308 Win w/ 200.20x and Varget
Qty3 43.3gr CCI BR4 Qty3 43.3gr GM250M
Qty3 43.5gr CCI BR4 Qty3 43.5gr GM205M
Qty3 43.7gr CCI BR4 Qty3 43.7gr GM205M
Qty3 43.9gr CCI BR4 Qty3 43.9gr GM205M
Qty3 44.1gr CCI BR4 Qty3 44.1gr GM205M
Qty3 44.3gr CCI BR4 Qty3 44.3gr GM205M
Qty3 44.5gr CCI BR4 Qty3 44.5gr GM205M
Qty3 44.7gr CCI BR4 Qty3 44.7gr GM205M

Shoot it. Find your flat spot. Park your powder charge between the flats.

That's the theory as I understand it anyway.

I've tried this in the past with basically zero success, but admittedly I didn't put a ton of effort into it. Recently though, with components being as scarce, the idea of quickly identifying loads became very appealing, and I figured I'd give it a serious attempt.

The first attempt is on a .308 FTR rifle with a new Krieger tube; the 8th barrel cut off this reamer. I have a pretty good idea as to where it's going to tune in. I know it's going to shoot a 200.20x, and I know it's going to shoot N150. Primer, charge weight, and depth (+/- .005 from where it always is) are basically all I have to contend with.

I perform the test from 44gr - 44.8gr with both CCI and Fed primers. Per the chronograph velocity flat spots, my ideal charge is right at 44.3gr (this is plausible based on all my other barrels). I do depth testing and the barrel looks ok, but not what I'd call good or great. I find a good depth and get to it.

After two club matches with the barrel I decide to go back to load testing my old way. I re-do powder testing (keeping same depth) looking for vertical on target, and end up at 44.6gr (also plausible). I re-confirmed it again this past weekend, and the gun hammered at 44.6gr....way better than the 44.3gr "chronograph node".

I've had the same experience with a 6BRA over the past month. I am just getting into this cartridge, so I don't know where it'll tune like I do with the .308. I tried tuning with the chronograph, and it just shot ok. I re-did it based off on-target vertical, and it seems to shoot much better.

So...that begs the question...those of you identifying powder/primer combos for F-Class loads using only a chronograph...what am I doing wrong? Enough smart guys proclaim to use this method that I'm confident it works...I just can't seem to make it work....selecting loads using vertical on target may take more rounds, but it works for me every single time.

tl;dr - Mike not smart. Mike no find powder node with chronograph. What Mike do wrong?

 

[Belly Benchrester]

thats interesting! Although i will say my last barrels were both cut with the same reamer. my bartlein settled in at 43.9 and my kreiger at 42.9 of n140. at the 2610-2615 fps node and 200's Both using n140, Br-4s and palma brass. both 30" barrels. two different lots of n140 but i doubt the lots vary by one whole grain. i usually just shoot groups and work up in .2-.3 grains till i see what i like then do seating depth, neck tension and sometimes tuner

 

[Cfshooter]

Way more in depth than what I may do, but one thing I have always found held true was results on a target. I will develop with chrono looking at velocity and POI, and then test on target to verify and almost always have to "true" my dope from target results. Use info from both will probably help get best results.

 

[Jdne5b]

I tend to pretty much see PRS type shooters doing the flat spot\chrono work and most Effers I talk to test at some distance letting the target tell the main story, not the Chrono, and then verify at longer distance if they initially tested up close. (100-300).

I pretty much only test at 600, and only Chrono out of curiosity after I've found a load.

I *think* one could find a good .5-.75 moa load using the flat spot method, especially with the equipment we have now days. With a custom rifle, a 6br cartridge, and 105hybrids.. it's pretty hard NOT to be sub moa from what I've seen (could be exceptions to this but in general they shoot very well), and for a lot of people, that's good enough. For me, for Fclass (FTR) I need to be sub-half moa in good conditions at 600.

TLDR.. Mike need to read target, not Chrono.

 

[davidjoe]

tl;dr - Mike not smart. Mike no find powder node with chronograph. What Mike do wrong?

Mike shoot big big score Sunday. Mike win TR long throws. Mike 1 point less Open. Mike make more better gun?

 

[MikeMcCasland]

I tend to pretty much see PRS type shooters doing the flat spot\chrono work and most Effers I talk to test at some distance letting the target tell the main story, not the Chrono, and then verify at longer distance if they initially tested up close. (100-300).

TLDR.. Mike need to read target, not Chrono.

I tend to agree with this observation; it's mostly PRS guys trying to have chronograph battles with each other. That said, I have also noticed a few of the big named F-Open folks claiming to do it for their load dev. I'm not going to call them out by name, but I've seen them make mention of it here, as well as on the YouTubes.

I don't think these guys are saying it to mislead either; I genuinely believe it works for them...so I'm left to assume that I'm doing something wrong.

Mike shoot big big score Sunday. Mike win TR long throws. Mike 1 point less Open. Mike make more better gun?

Hah! That's hilarious. I don't want to make anything better, I just want to arrive at the same conclusion while expending fewer primers on new tubes/new cartridges.

Mike no waste primer. Mike want answer faster. Mike seek answer smart people.

 

[CharlieNC]

Barrel harmonic oscillation is not reflected by the Chrono, but does greatly affect the target.

 

[PopCharlie]

I shoot short range benchrest for fun. I don't compete. I do like shooting tiny groups. I use a chrono to do powder/ primer testing. I shoot 1 round for each charge, low to high, in .2 gr increments. I like to see 3 flat spots, low, middle, and high. From there, I select a powder charge that is in the middle of a flat spot. Then seat bullets (for my 6br) at jamb, -.003, -.006...etc. 5 shots each. When I find the best, meaning smallest group, that's my load. I will say that this method is not always successful or repeatable. The only reason I test with a chrono is to find a starting point for powder and primer. I'm going to follow this thread because I want to find a better way.
How does one select a powder charge when starting a new load development project?
PopCharlie

 

[Ned Ludd]

One potential problem with searching for a "flat spot" in the charge weight vs velocity curve is the sample size (n). Even when using 5 shots to determine velocity, it is possible to have an outlier or two that alter the interpretation of the resulting curve. Three shot groups would make this endeavor even more difficult.

The notion of "flat spots" in the charge weight versus velocity curve is not new. Over the years, I have read a number of posts here where members stated that they use this approach. I also personally know a couple of excellent F-Open shooters that swear by it. Having said that, I have never seen a "flat spot" in a velocity curve loading .223 Rem or .308 Win that actually held up on repeated to the range. There would seem to be a solid "flat spot" on one trip, but it would disappear the next. This is where I believe using such a small sample size may be a contributing factor. However, it is also difficult to come up with a rational explanation of exactly what would be happening in terms of combustion/internal ballistics to explain the existence of such a "flat spot" in terms of physics/chemistry. The notion of a "flat spot" in the charge weight versus velocity curve cannot be explained by what I know about physics/chemistry. In fairness, that doesn't necessarily mean much. There is a LOT I don't know, and just because I don't have a rational explanation for something doesn't mean it doesn't exist.

As an alternative view, in discussion of this topic here and elsewhere, I have noticed that the presence and magnitude of "flat spots" in such curves seems to be very pronounced in much larger cartridges than I reload. In fact, it seems as though the larger the case capacity, the wider and more obvious the "flat spot". So one explanation of why I have never reliably observed such "flat spots" could be that .223 Rem and/or .308 Win cases are small enough that other variables in terms of velocity variance might be masking them. I have also been told by a very reliable source that if the "flat spot" couldn't be observed from a specific charge weight/velocity test, that that was a good indicator that different primers should be tested, until one was found that reliably showed the "flat spot". I typically use Fed 205s for almost everything, so this could be another explanation why I haven't observed these "flat spots".

At the end of the day, what would really be interesting to see would be a well-defined and repeatable "flat spot" in a velocity curve, tested using a "ladder" format, so that the relative bullet impact height on the target within the "flat spot" region could be compared to the shots of higher/lower velocity within the test range. I do not recall ever seeing anyone do a test this way, or at least, where both data sets (i.e. charge weight/velocity and vertical impact) were shown together. If one were planning to use the "flat spot" approach for load development, it would be nice to know how vertical on a target at some distance was affect within the "flat spot" velocity region, as opposed to simply printing groups at 100 yd or so.

 

[Dub]

Great info Ned

 

[jelenko]

While completely agreeing [recognizing that my level of expertise means my agreement doesn't mean much] with the sample size issue, I wonder if flat spots would be caused by 'quiet times' at the muzzle so that the muzzle is essentially pointing in the same direction.

Ignore my comment about 'quiet' times. That would affect POI, not MV. Well, just, duh.

 

[mikecr]

Well there are at least 3 node types.
Powder burn
Vibrational
Recoil
The combinations leading to dynamic results (summations/compensations).
With this, there is currently no prediction,, only target validation.

I've never seen an MV flat spot. For me, when powder goes up, velocity goes up, even when 100% burn was never attained.

 

[PopCharlie]

Great posts from Ned Ludd and Mikecr

 

[PopCharlie]

As a follow up from my earlier post, I read somewhere that you should pick a powder charge on the low side. Then do seating depth testing. Once a seating depth is found, walk the powder charge up to get the best velocity.
There is a big assumption in all of this. That being the shooter is capable of shooting well from a bench. I'm not, at least not consistently.

PopCharlie

 

[Keith Glasscock]

Flat spots do exist. As has been noted by others, those flat spot may or may not align with the vibrational behavior of the rifle in whole. When the two marry up, it's like magic. Otherwise, it's a waste of time.

I tune by POI, but chrono at the same time to look to see if I'm in a flat spot, because that tells me if my ES/SD is going to be good or not. Sometimes, the picture in the crystal ball is cloudy, and good POI happens too frequently. I sort that out by velocity flat spots.

I always verify at long range, anything I decide at short range.

 

[RegionRat]

It is never as easy as the internet tries to make it sound. For an example of a single charge sweep, along with the verticals that Nedd was talking about, I can offer an example from last year with a fresh barrel. This is a 30" 6 Dasher with Berger 105 Hybrids using Varget and CCI 450 with virgin Alpha brass. I use guess for the first seating depth so these are all at a jump of 0.010".

The Blue plot is velocity on the left, the red plot is the vertical component on the right at 600 yards.



Here is what that target looked like.

 

[MikeMcCasland]

It is never as easy as the internet tries to make it sound. For an example of a single charge sweep, along with the verticals that Nedd was talking about, I can offer an example from last year with a fresh barrel. This is a 30" 6 Dasher with Berger 105 Hybrids using Varget and CCI 450 with virgin Alpha brass. I use guess for the first seating depth so these are all at a jump of 0.010".

The Blue plot is velocity on the left, the red plot is the vertical component on the right at 600 yards.

View attachment 1259517

Here is what that target looked like.

View attachment 1259521

That's a very interesting analysis; appreciate your contribution as always. If I were just looking at the spreadsheet I'd say park it at 31.65gr and call it good. With the shotmarker data added to it, I'd run it at 33gr and not give it a second thought.

I'm probably going to steal this. I assume you manually input the data into excel? There's no way to easily export from your LR and shotmarker?

Edit: Somewhat related, I've found enabling the mean radius stat on my SM really helpful. Noticed you don't have it on; figured I'd make mention.

 

[Bc'z]

It is never as easy as the internet tries to make it sound. For an example of a single charge sweep, along with the verticals that Nedd was talking about, I can offer an example from last year with a fresh barrel. This is a 30" 6 Dasher with Berger 105 Hybrids using Varget and CCI 450 with virgin Alpha brass. I use guess for the first seating depth so these are all at a jump of 0.010".

The Blue plot is velocity on the left, the red plot is the vertical component on the right at 600 yards.

View attachment 1259517

Here is what that target looked like.

View attachment 1259521

This is what I'm not grasping....
Shots 17&18 are plotting a flat spot in velocity but vertical on target.
Shots 15&16 are plotting vertical but horizontal on target.
Sharing load tune information with another member I've seen his chronograph #'s for charges shot against the target. I remember 1 target in particular 3 shots per charge, one of which had the same velocity for all 3 shots but a very open grouping, whereas a charge with a variation in velocity of 6-8fps grouped the smallest.

 

[Tokay444]

I don’t believe in flat spots. Anytime one has presented in a load test, it hasn’t been there again any other time the test was duplicated. I see a very direct correlation in rise of velocity with increase in charge weight. Certain charges will have better ES/SD than others, but there is no flat spots in velocity.

 

[RegionRat]

That's a very interesting analysis; appreciate your contribution as always. If I were just looking at the spreadsheet I'd say park it at 31.65gr and call it good. With the shotmarker data added to it, I'd run it at 33gr and not give it a second thought.

I'm probably going to steal this. I assume you manually input the data into excel? There's no way to easily export from your LR and shotmarker?

Edit: Somewhat related, I've found enabling the mean radius stat on my SM really helpful. Noticed you don't have it on; figured I'd make mention.

When you spend enough time doing analysis in your life you get used to things like MatLab, Minitab and Excel, it takes seconds to transfer the ShotMarker or LabRadar data. Both SM and LR are creating files that are readily turned into graphs using Excel or Matlab. When I get done with a day of development tests, I dump the SM and LR data into files and folders by barrel and caliber.

When I am just holding on a dot and pulling the trigger during charge or depth tests, I am only looking at the vertical, so the Mean Radius doesn't help me cause I am only looking at the vertical component and ignoring the horizontal. When I go back to verify actual groups, I do pay attention to group stats.