Optimal Barrel Time and Quickload

[NZVarminter]

This one is for Techshooter, but others feel free to provide input.

I have a 22BR on a Stiller Predator with a local (NZ Hardy)) Np 4 contour match grade barrel with 1:8 twist 6 groove.

I've been reading up on accuracy nodes. Looks like there are three variations to the "ladder" technique to find the accuracy nodes:

1) Dan Newberry's Optimal Weight charge technique.

http://optimalchargeweight.embarqspace.com/#/ocw-test-example/4529811475

Dan uses group size and position to pick the sweet spot

2) Chris Longs Optimal Barrel time theory

http://www.the-long-family.com/OBT_paper.htm

Soundwave theory...makes sense but looks difficult to calculate accurately without pressure trace.

3) Steve Laurence technique where he looks for the minimum velocity spread. See 6.5 guys vid

http://www.65guys.com/load-development-part-2-of-2/

As I have a 100m range at home, I want to try Steve's technique that relies on the velocity plateaus and minimum velocity spread to identify accuracy nodes as velocity is independent of the distance I'm shooting and a ladder test at 100m has too many overlapping shots to be easily interpreted.

I've just shot 11 x 5 shot groups from 29.9-32.9g on 0.3 g increments and here are the results:

Hmm having problem getting a readable image of my chart and this site wont let me upload the xls file.

My confusion is that the tightest groups are where there is the largest velocity spread, which is the opposite of what I was expecting.

I've modeled the load in Quickload and had to do quite a bit of fudging to get it to match my range velocities. Chris suggests changing the BA value and projectile weight to fudge QL to get it to match range velocity, but changing the BA and projectile weight only move the velocity up or down but parallel to standard values. The only way to vary the gradient of the velocity line appears to be to change the cartridge weight factor. I had to change this from 0.6 to 0.2 to lift the gradient of the velocity line to match my range velocity.

Once I got a reasonable match I calculated the OBT nodes, which I've added to the chart. Node 4 is pretty close to one of the velocity plateaus, but not where I shot tighter groups. Node 3 is also close to a marginal plateau but these OBT points are not really showing good correlation with my ladder test.

So where do you suggest I do further testing for my accuracy nodes?

 

[dcali]

I think the elephant in the room is that OBT is not important. I get branded a heretic for saying this, but the effect (although it seems entirely plausible that it's real) just doesn't make sense as a primary driver of accuracy. Rifle dynamics are just too complex to be captured by such a simple model.

Vibrations are real. Barrel whip is real. It all matters. But OBT doesn't capture *how* it matters. In my opinion, when it works, it works by chance. I do know some fantastic, smart shooters who swear by it, but I just can't get to the point where I'm convinced this isn't a dead end of a rabbit hole.

Now I'm going to go duck behind some cover...

 

[Sheldon N]

I've seen the same thing in one of my rifles, the tightest groups and the nodes from the OCW style tests weren't necessarily the place where the rifle gave the lowest ES and SD. I have seen that the OBT nodes match closely (but not perfect) with where I found OCW nodes and tight grouping.

My current approach is to use preliminary calculations from QL to know roughly where I should expect the OBT node to be, then conduct a shooting test using the OCW method to find a stable node, then tweak seating depth.

I would love to correlate all the above with chrono data, but I'm using a magnetospeed and don't do load development testing with anything attached to the barrel. Maybe someday I'll get a LabRadar.

One thought on SD versus tight grouping... Imagine you've got a 1/2 MOA difference in group size between the load with low SD and a load with higher SD that shoots tighter groups. You can run the math on what yardage the crossover point would be that the smaller group would start to give greater vertical dispersion due to SD. Ultimately we're looking for a load that gives the least amount of vertical variation at distance, and that may or may not be the load with the lowest SD.

 

[BoydAllen]

(This is an opinion, one mans. Others may disagree. That is to be expected)

Look, either the tools work or they don't. The object should be to identify accuracy nodes, and those should be defined by looking at TARGETS, not spread sheets or charts. I am always amazed at the lengths that people go to to bench race load development.

On a day when conditions are reasonable for such a task, show up at the range with your reloading equipment and components, a chronograph, and a set of wind flags. You can preload the first part of your test, two shots each of progressively heavier charges with increments suitable for the case capacity that you are working with. For a 6PPC I use .3 grains, more for larger cases, less for smaller. After firing a few fouling shots, shoot each pair into its own aiming point as rapidly as you can reliably do so, to have the greatest chance in getting them both off in the same condition. Obviously you will be looking for patterns in how the wind behaves, and doing some guessing as to when it is likely to hold for ten seconds or so. Take your time so that barrel heat does not become an issue. Clean and re-foul if your rifle requires that. This is all predicated on the rifle being in such a state that you believe that variations in groups are primarily the result of differences in the loads. After shooting The stepped charges to the point where pressure signs tell you it is time to stop. Go back and look at your targets. You will be looking for a pattern of opening and tightening of the groups. Note the spacing in terms of charge weight, and the number of groups that hold reasonably tight that are adjacent to each other in charge weight. Pick one or two middle charges in these groups and do some testing with larger numbers of shots, paying close attention to your flags. If all as gone as it should, you should have identified your most promising nodes. If nothing shows up, pick other components to test. Loading at the range, and the use of wind flags are the key. Obviously all of this would be a waste of time if your rifle had any issues like imperfect bedding, or a scope problem. A proper rest setup, decent trigger weight, and sturdy bench are also required.

Added later the same morning: I neglected to mention seating depth. Unless there is a strong reason not to, I usually do this test with bullets seated so that marks from the rifling are half to one third as long as they are wide. An exception would be when working up a load for a no-lead bullet that the manufacturer recommends be jumped.

 

[waldo1979]

Vibrations are real. Barrel whip is real. It all matters. But OBT doesn't capture *how* it matters. ...

The OBT paper talks about concusive waves vs. linear waves. The idea is that acoustic waves travel between the bolt face and the bullet base slightly propelling the bullet. If the bullet exits the muzzle just as one of these waves hits it then it is destabilized.

May be a load of crap, but the barrel time model does seem to work. Assuming your Quickload model is accurate, the OBT times will be pretty close to your accuracy nodes. If not, the OBT for your barrel will likely be consistent across different loads.

 

[dcali]

The OBT paper talks about concusive waves vs. linear waves. The idea is that acoustic waves travel between the bolt face and the bullet base slightly propelling the bullet. If the bullet exits the muzzle just as one of these waves hits it then it is destabilized.

May be a load of crap, but the barrel time model does seem to work. Assuming your Quickload model is accurate, the OBT times will be pretty close to your accuracy nodes. If not, the OBT for your barrel will likely be consistent across different loads.

I know what it *says* matters. But there are two issues I have with it. One is that the magnitude of the barrel disturbance claimed in the paper is too small to matter - it's a smaller dimensional change than the surface finish of the steel, and certainly smaller than the difference due to bore pressure. Second is that it's a *radial* disturbance. How is that going to change the direction of the bullet?

Throw in that there are all manner of other things going vibration-wise on that observable and measurable, and I just can't get worked up about one small, probably negligible effect, even though it's academically cool and interesting to my inner nerd.

That, and I haven't actually found it to work in practice.

 

[CharlieNC]

OCW and ladder testing are not about selecting a charge based on group size, but on minimal change of vertical point of impact. Those nodes have always been pretty close to OBT calculation for me, including multiple nodes for a given workup using several different weight bullets. If you refer to Varmint Als finite element analysis for numerous barrel harmonics I think you will see one of the major ones corresponds to the OBT based harmonic. Doesn't mean there could be some unusual over riding condition.

 

[BoydAllen]

Assuming the chosen components, rifle and test setup have the potential, I can be finished with everything that I described in a morning with time to spare. I understand the theories, but for me it is just a lot easier to do the testing. What I think that most are trying to get away from is loading at the range, and learning how to do a little wind flag reading. Most of my friends have a basket full of reasons why they cannot take a direct line from A to B when working up a load.

 

[dcali]

Assuming the chosen components, rifle and test setup have the potential, I can be finished with everything that I described in a morning with time to spare. I understand the theories, but for me it is just a lot easier to do the testing. What I think that most are trying to get away from is loading at the range, and learning how to do a little wind flag reading. Most of my friends have a basket full of reasons why they cannot take a direct line from A to B when working up a load.

I'm with you. And I would even go as far as saying that loading at the range isn't necessary for anything outside of benchrest, although it's preferable if you've got the gear. But shooting is going to be more reliable than calculating every time on this stuff.

 

[CharlieNC]

Boyd for me the primary use is not actually a shortcut for load development but in helping to choose between options when it comes to selecting new calibers, bullets, powders, barrel lengths, etc. Especially considering long range options to find if a node is likely at the upper velocity limit within pressure max. Having seen a good correlation with obt leads to confidence in limiting the number of options to evaluate vs an extensive list.

 

[BoydAllen]

It sounds like that wrench is a good fit on what you need tightened.

 

[NZVarminter]

I'm not trying to avoid load development at the range as I have my own 100m covered range, so I want a technique that will work at 100m to I only have to go to my clubs 300m range to confirm my preferred load. My range is covered, so wind is one variable I have substantially removed (though may have introduced another variable with thermal incline...time will tell on that one).

Problem with 100m is you any trends in POI movement are very small and can easily be missed by other variable. Thats why I was hoping charting the velocity would help me pinpoint where to focus my load development. Hell I've done 12 shot ladder test at 100m using a single case with 0.3g increments over 3 grains and 300fps and the total group has measured under 1". Then I pick what I think is a good start load out of that test, load up 3 rounds and shoot them and they go well over 1"! go figure!@#$%^

You can see loads 8,10 and 11 have noticibly more horizontal in them. This cant be wind, but could be my poor shooting technique but I didnt call any of these as "pulled", so I'm picking these are the scatter groups between nodes?

My pick would be to do a 0.2 increment around loads 5 and 6 which both shot 0.44 and have very similar POI....but they have larger velocity spreads!

I havnt annealed my cases since forming, so maybe variable neck tension is influencing my velocities, though seating pressure feels reasonably consistent. Think I need to repeat this test and see if the velocity spread is repeatable.

 

[NZVarminter]

One more thought... I cant understand why my real world velocities are so much higher than Quickload predicts? QL says 31.4 is over pressure, yet I have no signs of pressure at 33g.

Maybe my Styner Super Chrony is reading high? might set my old one up as well and see if they read similar.

 

[waldo1979]

One more thought... I cant understand why my real world velocities are so much higher than Quickload predicts? QL says 31.4 is over pressure, yet I have no signs of pressure at 33g.

Maybe my Styner Super Chrony is reading high? might set my old one up as well and see if they read similar.

I get a little of the same. maybe 50fps high. Is your case volume accurate?

 

[dcali]

I think people have expectations that are too high for Quickload. If it's getting you within 50 fps out of 3000, that's just a hair over 1% accuracy, which is pretty damn phenomenal for a few equations and some lab data. There are limits to engineering software.

 

[NZVarminter]

One more thought... I cant understand why my real world velocities are so much higher than Quickload predicts? QL says 31.4 is over pressure, yet I have no signs of pressure at 33g.

Maybe my Styner Super Chrony is reading high? might set my old one up as wll and

 

[NZVarminter]

The reason I'm tweeking QL to match my real world velocity is so I can calculate as accurate as possible OBT time....But at the end of the day, yes it holes in paper that tells the true story! And the more I look at velocity the more I realise chronos are only accurate to a degree, and mine seems to be the least accurate!

 

[Ned Ludd]

Powder burn rates are dependent on pressure, temperature, and probably a slew of other factors. Due to different cartridges, bullet weights, and additional load-dependent variables, there is not an easy way for QL to list a single burn rate factor for a given powder that will be spot on across a wide range of loads and other variables that occur during its use. I have typically found QL velocity predictions made using the factory preset Ba to be within 50 fps [ballpark] or so of actual values. As damoncali noted, this is pretty close in the grand scheme of things. However, it is the main reason I always look for the highest predicted OBT charge weight under MAX pressure using the preset Ba first, then reduce that by 2%, load some rounds, and determine actual velocity to "calibrate" QL for my specific setup. Because the initial OBT charge weight predicted using the preset Ba is already under MAX pressure, I have found the additional 2% reduction in charge weight to be more than sufficient to prevent inadvertently starting out with a charge weight that might be over MAX pressure due to the inherent uncertainty.

 

[dewey7271]

I have typically found QL velocity predictions made using the factory preset Ba to be within 50 fps [ballpark] or so of actual values.

Running a number of different cartridges with a bunch of help from friends has shown recently that the Ba on a fairly recently released powder is off sometimes quite a bit depending on cartridge. The burn rate needed to match actual velocities has varied significantly depending on cartridge.
Cartridges run were from 243 to 338 with the samples. Ba varied from a low of .330 to .372.
Just FYI.

 

[Webster]

Running a number of different cartridges with a bunch of help from friends has shown recently that the Ba on a fairly recently released powder is off sometimes quite a bit depending on cartridge. The burn rate needed to match actual velocities has varied significantly depending on cartridge.
Cartridges run were from 243 to 338 with the samples. Ba varied from a low of .330 to .372.
Just FYI.

You have to keep in mind that burn rates are not determined using a rifle. They use a cylinder with a hole in one end. No case, no primer, no bullet no barrel. I think they use the same cylinder volume powder charge for all the various rifle powders? All you can say is all the powders were tested under the same conditions even if they don't relate to some particular cartridge or bullet.