Optimal Barrel Time Concept

[Howa 9700]

Anyone familiar with this?

http://the-long-family.com/optimal barrel time.htm

Seems there is supporting documentation if you think about it. The Satterlee ladder test.......recall reading where Scott Satterlee said that once he had ID'd the optimal velocity for a gun and bullet, he would get the same results regardless of powder.....as the bullet reached the same velocity.

And one more observation. Doing some research on these ladder tests, I have seen a lot of instances where guys graph their velocities to ID the flat spots. Likely as not, those seem to appear about half to 1 grain short of maximum load data......at a point where case is going to be full of powder....and right o the edge of being a compressed load. A full case load of powder was one of the key conditions the OBTC author had identified as contributing to accuracy.

It all starts pointing in the same direction.

 

[Hooda Thunkit]

I've been playing with Gordons Reloading Tool (GRT). The algorithm in it has an Optimal Barrel Time (OBT) listed, and it changes with powder charge, bullet weight, seating depth, etc.

TBH, through the years I haven't paid much attention to it, probably to my detriment. I really haven't had the computing power necessary to make any sense of the concept. I've always used the hit-n-miss method.

I think that's going to change. I'm fixin' to start playing with a Howa Mini-action in 223. I've got several bullets and 6 -8 powders to try. Instead of just burning components I think I'll set something up in GRT and see if the OBT concept has merit.

It certainly makes sense on the surface.

 

[GHinNH]

There are far and above more qualified people who run GRT than me, so this is just my observation. It took me a while to figure out the OBT tool but after reading the manual and discussions on the GRT discord, and also some experimentation I believe I have a grasp on it.

It is said that using Long's theory of OBT will get you sub MOA without needless ladder steps. It took me a while to grasp the concept of using it correctly with GRT and you need to choose which ladder step shows the best accuracy to run it with.

As long as the OBT tool in GRT is used correctly my experience is it's pretty darn close to right the first time. It requires real world numbers, so If I run a new to me powder I go through the usual process of a ladder load. After adding chrono numbers to the measurements tab, and making adjustments to the IP if needed, the OBT is run and then saved as a grtload OBT file.

Then the "compute node charge adjustment" is clicked to find the theoretical optimal charge. Sometimes that node charge is too high so it also supplies 1/2 or full nodes up and down from there, so you can choose the one you want.

My personal experience, after running the OBT tool I have found it lines up very close to my accuracy observations when running a ladder load, so my confidence level with it is quite good.

 

[Howa 9700]

Well crap............turns out there is a whole Gordon's Reloading Tool channel on U-tube that explains all this. Something like 80 videos. There is a week shot!!!

https://www.youtube.com/channel/UCEdG4IMYRhSA4Tc09hUKN_A

 

[Varminterror]

Personally, I don’t believe the Satterlee method proves different powders at the same muzzle velocity with the same bullet will hit the same node. It just doesn’t happen. Been there, done that.

I also don’t believe the Satterlee method backs up the OBT method, as I have ridden barrels on significant velocity losses as the barrel wears out, and the node indicated by the Satterlee method has coincided with the powder charge, not the constant velocity or barrel time. Been there, done that too.

And to restate, in following the OBT, I simply have not found the TIME to be a reliable predictor of a node - naturally, when we do our initial test, the specific velocity corresponds to a specific barrel time, but as the barrel speeds up during break in and then slows down as it wears out, the node doesn’t move away from the powder charge, it doesn’t stick with the velocity, doesn’t stick with the dwell time. The node sticks with the powder charge.

I expect that’s one reason we hear so little about the Long OBT compared to the Newberry OCW, Audette Ladder, and Satterlee Velocity profile... these 3 don’t seem to break apart as easily under scrutiny. But breaking OBT theory happens a few times every barrel...

 

[Howa 9700]

Clearly I'm new to all this and still learning, so not in a position to say one way on the other as far as Satterlee. But this is where I got that from...(the part about same velocity nodes using different powders)...and as for his ladder test and my connection to OBT, that is just me speculating. When you drill down into what both are doing, it gets to be remarkably similar. Different approaches to get there, but apparently similar end results....both in methods and outcomes. One a trial and error approach, the other a mathematical calculation that explains the trial and error results.

http://www.65guys.com/10-round-load-development-ladder-test/

One thing I like about the OBT concept is it at least sounds plausible. I've been wrestling with the concept of barrel harmonics, and as I've seen it explained even in credible sources like my Lyman reloading manuals, that did not make sense. They describe it as barrel vibrating up and down like a tuning fork. Clearly barrels do vibrate, but most of that after bullet is long gone.

The OBT concept of pressure induced waves traveling up and down the barrel, and timing of bullet movement relative to those waves sounds more plausible.

 

[Varminterror]

Whip oscillation has been proven to NOT be independent in “barrel harmonics.”

Read up on positive compensation.

Equally, recreate your Satterlee curves and OBT tests with the first shots, 200th shots, end of barrel life, and twice useful barrel life. You’ll see for yourself the node hasn’t shifted, despite velocity increasing and decreasing. Without question, the groups can still be itty bitty, but the stability node typically doesn’t follow the velocity. When every shooter in the country can witness this for themselves, it really proves the barrel time simply doesn’t correspond independently. Most folks simply don’t do load development repeatedly with the same components over the life of a barrel, and further don’t compare the results for this objective.

Remind yourself also - barrels will be oscillating in a MHz frequency - this means there are multiple frequency nodes where a given velocity would align with the nodes of the wave. This is far smaller scale than the nodes we see in load development - when we see nodes 50-200fps apart, even knowing that a bullet dwell time is only on the millisecond scale, we know a velocity curve would cross oscillation nodes THOUSANDS of times between the nodes we observe.

And of course, when we change combustion mechanics by changing our powder charge, we’re changing the energy which initiates the oscillation.

AND of course... the same velocity with a given bullet (proven valid in many competitive shooting cartridges) is proven to work in many barrel contours and lengths. We know these don’t have the same barrel time...

AND of course... we can see the same powder charge node appear in extremely different barrel lengths, despite extremely different velocities. Certainly my 24” fluted heavy sporter has a different natural frequency than my 15” Competition contour pistol barrel, and different than my 24” heavy AR barrel, and different than my 26” heavy Palma, and different than my 26” M24... but they all have nodes in the same powder charge, despite EXTREMELY disparate velocities.

So I don’t buy the barrel time relationship at all. It breaks apart at every corner.