Optimum Barrel Time and Accuracy Nodes

[LRRPF52]

Maybe once htey release it. I have versio 3.6 (what NECO is selling) and it does not have the latest powders. Hopefully within a year it will be updated. There have been a lot of powders introduced in the past year or so.

I have been using it for a year now and it is not cut and dry with loads. It is a reference tool only. It does not replace load manuals. So far, I have not been able to have it come close to my real world data from my Oehler 35P and manuals.

Welcome to the forum, hntbambi. There's a new member thread where you can tell us about yourself, your Grendel interests if any, and so forth.

[Rambozo]

Well, the version I have has stuff like XBR8208, so you guys must be using an older version.

As for the accuracy of the program. I've found it to be quite accurate. But this is like any software program for ballistics and reloading. It's only as good as the information you give it. Are you using the default cases and bullet dimensions and capacities? For accurate results, you have to measure this stuff yourself. I know that there is enough difference in the capacity of my Lapua brass and Remington brass to produce drastically different outputs from the software.

As for optimal barrel time; this is something that I've spent time toying with. The problem is that I don't believe it to be the single primary consideration. It makes sense, but I've stopped paying attention to it. Quickload seems to be essential for determing it, but again, it relies on good source information. Even still, it seems to me that the windows between accuracy and scatter nodes is wide enough that it requires drastic shifts in velocity to move between one or the other. I've really stopped paying attention to it.

My reloading technique is entirely different and simplified. I work in .5 gr charge incriments based off of my theorhetical max load in 5 shot groups. So I define my loads backwards across the load range. I generally do a .020 jump and pick whatever primer I want (Wolf or Winchester). Generally, I can find a promising load this way. Next range trip, I can work on variations.

I try not to over think these things, because it's easier to find more questions than it is answers. lol

[JASmith]

...I try not to over think these things, because it's easier to find more questions than it is answers. lol

I can relate since I am frequently "wrongly accused" of over thinking these things. How else does one find interesting questions and frequently even more interesting answers!!??

Sometimes the accusers have a point.....

[bwaites]

Have we discussed this before? I just came across these concepts, and found them very interesting. Basic premise is that the longitudinal shock wave that resonates from chamber to muzzle, then back and forth, significantly affects accuracy if the bullet is leaving the muzzle at the time the wave is at the muzzle.

Seems to be a lot of data to support that this is the explanation for unexplained open groups with certain charge weights, while others fall into certain accuracy nodes.

Apparently, Quick Load has a function to deal with this, called Barrel Time, measured in microseconds. The links have tables with the accuracy node figures for different barrel lengths.

I've had this feeling about load development and barrel harmonics that has been nagging me, with the suspicion that there is some type of physics behind accuracy nodes, but I just couldn't put my finger on it. Apparently, these guys have proposed one theory, and testing by various participants has shown that there is reproducible merit to the Optimum Barrel Time hypothesis.

Pretty crazy stuff.

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

http://optimalchargeweight.embarqspace.com/#

I met Chris Long at a match a couple years ago. He explained the stuff in pretty good detail, and I thought I understood SOME of what he was getting at.

I now have a new barreled 7mm WSM, and I'm trying to work this through, to prove my theory vs actual development, since I have no preconceived notions of what will shoot well in this barrel.

Anyone want to work it through for me, so I can double check my results vs. yours BEFORE I fire a round?

[JASmith]

I've just started working the 'optimal barrel time' for my new .243 Win but will need to get to the range a couple of more times before I start to get an idea of whether it might work. After that I'll tackle my son's Grendel.

[JASmith]

OBT a Failure?

I've done a little bit of homework and tried using QuickLoad to estimate loads that map into the OBT node matreix for my rifle. The problem for me is at least one of confidence. First, I would expect that QL would match the velocity for at least two loads to within a few percent to get a good barrel time prediction. The same is true of the maximum pressure because that's the region that will have the most impact on barrel time. I. e., the bullet is moving slowly there and small differences in pressure will have relatively larger influence on velocity than the same percent pressure error in the last half of the barrel where the bullet is close to its maximum velocity and accelerating very slowly.

There are some, however, who have reported fairly recent successes with the method (http://www.snipershide.com/forum/ubb...Number=2807521). It appears that they chronograph their own loads, suggesting that the method can work OK if your are willing to shoot a few rounds just to calibrate QuickLoad.

I have tried matching the highest and third highest velocities for the 87 grain bullet in the Hornady manual and finished the exercise with less than 100% confidence. Part of the problem here results from there being several different bullet designs for the same load data and we don't know which bullet or bullets were used in their testing.

I guess I'll need to look closer at gettin a Pro-Chrony...

[JASmith]

Alternative Paths to Optimum Accuracy Load

Bwaites has almost certainly developed his own methods to systematically get the best load for his long-range shooting. Many of us, however, probably haven't because we are just getting started in the sport of precision shooting so I'm posting the most salient one's I've looked at over the last few days. A cautionary note: these methods use up a fair fraction on one's barrel life unless he's using a Grendel, 223 Rem, or a .308Win. (Some of these may duplicate links from previous posts):

• Alternative to OCW from FrankenMauser at http://thefiringline.com/forums/showthread.php?t=445335
  
  This shooter reports getting a good load quicker and more cheaply than OCW "by finding powders that reach 100% density with a near-max, max, or barely-over-max load. I use that to calculate a 95% load, and it is nearly always extremely accurate and forgiving"
  
  The writer indicates also that it is important to first determine what the safe loads are...
  
  
• Ralph Constantine gives an excellent explanation and illustration of the Audette Ladder system. The file is downloadable http://www.desertsharpshooters.com/m...incredload.pdf
  
  
• Ladder vs OCW: Jason Baney, , has an excellent discussion about how to implement the ladder test for 1000 yard competition. His technique lets him get 2" vertical dispersion for three shots at that range, sometimes just one-inch. That's 0.1 moa!
  
  The technique, however, looks like it takes about 100 shots. This is about 10% of the barrel life of large capacity cases like the 20 BR, 243 Win, 7mm WSM, etc. http://practicalrifler.6.forumer.com...ic=363&start=0

[CTone03]

I've used the ladder system successfully in the past, but I had previously used the OCW system with the same load and had the exact same result. The load was a 308 win using RL17 and the 175 grain Nosler CC, and the node was quite obvious with both tests. Quickload wasn't very close at matching my actual velocities even when I entered in the water weight of my Winchester cases, but when I manipulated the temperature field in the program to make the velocities match, the "barrel time" field became very useful. So I knew from the ladder and OCW tests right where the node was, and then I used the barrel time field in Quickload to tell me what the best seating depth would be, which is the OBT method. I ended up with a great shooting load that pushed that 175 J4 at over 2,650 fps from a 20" barrel.

Again, I honestly see that one method is not exclusive; the OCW or ladder test locates the "node", and the OBT method locates the optimal seating depth. I think if you discount the usefulness of one method, you cheat yourself out of perfection.

[JASmith]

Ctone,

Thanks! That's very useful information.

I would not have expected that the temperature field would have enough influence on velocity & barrel time.

Did you try tweaking "Ba" in the powder menu? Any other fields?

Your experience also shows us yet another reason the chronograph is a very useful tool when questing for accuracy.

[CTone03]

JASmith - I've read on reloading forums where folks have tweaked the powder fields, but I don't know enough about them to mess with them. What I do is click the hand-with-a-pen on the right under the "selected powder" drop down, which makes a thermometer button appear right above "Apply and calc". Just by tweaking the temperature using that thermometer button, you can match your velocities very close. Usually if I have data from a string of multiple charge weights, I'll match the velocity in QL to the specific charge I'm interested in, and the rest are almost always within 10 fps or so.

I'm a believer in using a chronograph, but I've recently learned to use a test load/cartridge to make sure you're getting accurate velocities. Different lighting variables, temperature, and the small changes in distance from the muzzle from setting up one day to the next can skew your velocites, so being able to account for that is important. The best way I've heard of to do this is with .22 rimfire by keeping a 500 round box (or several identical lots of ammo if using a different cartridge) and shooting 2-3 rounds and recording it. This also ensures that the chrono is working right. I can't tell you how many times I've started an OCW test with handloads that I lovingly and painstakingly built, only to have the chrono miss the first several shots because the batteries were running low or there was a shadow across one of the sensors.

[JASmith]

Thanks for the info!

To date, I've tried tweaking the powder fields once, and wasn't comfortable with the results even for an OCW/OBT exercise. It is also possible that the results were not as consistent as I like because I ran the exercise against a table of data where the charge weights were given for even hundreds of ft/sec AND four different bullet types were listed for the same charge weight and velocity.

I'll try to find a more dedicated source for the powder/bullet combo I'm interested in and try the temperature knob in addition to the others.

[JOAT 0311]

This a great thread! Thanks!

[LRRPF52]

I noticed yesterday that when I shot my Lapua-brass .260 Rem loads with everything else being equal, my tight groups went from .4" when I use Winchester 7mm-08 necked down with 43.3gr of H4350 and 130gr Berger VLD's at 2840fps, to 2880fps and 1.5" with the Lapua brass.

There definitely is something to accuracy and the projectile leaving the barrel at a certain speed. I was able to shoot several .5" or better groups with the other loads until I started shooting the higher-velocity loads with the same components.