Why I think the Satterlee and Audette Ladder Tests Work and Why-- You Decide!

[Stammster]

I would not assume back pressure would necessarily decrease velocity.

 

[Veteran]

I would not assume back pressure would necessarily decrease velocity.

Curious why? Another form of backpressure is friction.
More friction definitely decreases muzzle velocity.

 

[Stammster]

My thought is that it would increase start pressure slightly and also prevent ever so less gas blow-by until the bullet engraves due more "static" air in the longer "effective" barrel length.

But then again, max internal pressure generally not believed to be a function of barrel length - so I'm probably wrong.

 

[aschler]

One other thought as the barrel harmonics cause sound and pressure waves to move back and forth in the barrel, the amount of friction the bullet experiences going down the barrel is also not a constant as charge weight is increased. So, small changes in bullet contact with the lands and rifling going down the barrel as it twists and turns due to harmonics may also be contributing factor to these flat spots in the velocity curve. A little more friction due to bullet resistance against an undulating barrel that is not perfectly straight for some milliseconds means less velocity at exit. All of these things play into counter intuitive physics results in the real world.

Here is an excellent source published in 1997 that essentially analyzes the Audette Ladder Test and says it works for the same reasons I explained above.

Man its all physics!


https://2poqx8tjzgi65olp24je4x4n-wpengine.netdna-ssl.com/wp-content/uploads/2012/07/incremental-load-development-method.pdf

By the way, I believe the whole reason you will find a low node, and a high node or several nodes that work where the graph goes up and then flattens again is related to barrel harmonics and sin waves of pressure and sound in the steel barrel.

Different combinations of harmonics are produced with different charge weights, bullet seating, etc. So, you may find a higher velocity node where it all flattens or goes down because the harmonics happened to come back into play again just right.

So as in electrical harmonics, you may get a 2nd, 3rd, or 4th order harmonic sin wave at some different frequency as you go up the velocity curve and find another node. I believe its all related to unique system harmonics in your specific rifle with its specific barrel
taper and length, and weight, the powder burn rate, the volume of the cartridge, the bullet seating used, the weight of the bullet,
etc. Then its all vibration of that barrel as the sound and pressure waves move back and forth before the bullet exits.

Explanation of harmonics and orders of harmonics -- ie, sin waves


https://www.electronics-tutorials.ws/accircuits/harmonics.html


Now, I don't have scientific proof from a lab to prove what I think......Lots of this is my own rationalization of what I see in the data and the graphs in searching for the answer why???? You might say it is a very good hypothesis. I would say yes, I agree, but to prove all this in exacting pinpoint precision will take a major army DOD lab or a major gun or ammo manufacturer to set up a test rig in a lab capable of measuring and logging pressure data at many points along a rifle barrel, shooting actual ammo with differing charge weights, and analyzing the barrel harmonics of that rig in milliseconds of time as each shot is made and chronographed. It could be done, but not by me or you. But, its the only explanation I think matches why this occurs and occurs
at intervals along the curve with lower, and higher nodes. Now, if anyone else has a better explanation, man I want to hear it.

Remember, don't give me any BS about monte carlo runs and statistics. The lab could also run this experiment a statistically valid
number of times to get a 95% confidence level and I believe they would still see it on the graphs. Its real. I fire at least 4-5 rounds per charge weight when I do it, just to make sure I get better repeatable results.

There is a book called Rifle Accuracy Facts written by a guy who was the supervisor of the aeroballistics division of Sandia National Laboratories who doesn't agree.

 

[aschler]

Curious why? Another form of backpressure is friction.
More friction definitely decreases muzzle velocity.

It is pretty well documented that suppressors increase velocity and backpressure (similar to brakes but usually much longer) but I've never seen a causal relationship claimed. You are still going to have some pressure much higher than atmosphere pushing the the tail of the bullet longer than if you didn't have the suppressor attached to the bullet. All the brakes I have seen have some distance where the same conditions would be present, just for a much smaller distance. I would guess it was different atmospheric conditions causing the issue but we are only talking about a 0.7% difference in velocity so I could see it being a lot of things; condition of the bore hasn't been mentioned yet.

 

[Mikecr]

The only valid explanation is the barrel harmonics had changed by fitting the brake.

Perhaps your muzzle device mounting tightened or extended the muzzle.
Only a truth passes all tests.
Tape your muzzle brake to the outside of the barrel near the muzzle. Shoot across a chronograph, did velocity change? How about grouping?
You'll find barrel vibrations change, and velocity does not.

 

[Veteran]

There is a book called Rifle Accuracy Facts written by a guy who was the supervisor of the aeroballistics division of Sandia National Laboratories who doesn't agree.

I looked this book up. Its 305 pages and costs $160 used.....$2 to 300 new......but I found a free download and downloaded it. I am very interested to read it. Thank you for pointing it out.

 

[Veteran]

It is pretty well documented that suppressors increase velocity and backpressure (similar to brakes but usually much longer) but I've never seen a causal relationship claimed. You are still going to have some pressure much higher than atmosphere pushing the the tail of the bullet longer than if you didn't have the suppressor attached to the bullet. All the brakes I have seen have some distance where the same conditions would be present, just for a much smaller distance. I would guess it was different atmospheric conditions causing the issue but we are only talking about a 0.7% difference in velocity so I could see it being a lot of things; condition of the bore hasn't been mentioned yet.

The way to prove this out is Take some consistent ammo, say 10 rounds to the range with the can on your rifle. Fire 5 rounds w the can across your chronograph.

Then remove the can. Fire 5 more rounds right then, same day, location, temperature. See what the average velocity is of the two ways. I would be surprised if the avg. velocity from the 1st group was higher if you are shooting low ES groups both times. There may be so little difference that bad quality ammo would spoil the comparison.

But, I believe that the backpressure from a can would slow the muzzle velocity ever so slightly. If this is not true I want to understand why.

 

[parshal]

I've had the same ammo shot in two successive strings provide average velocity differences of near 10 fps with both labradars and magnetospeeds. Those are 5-7 shots for each string. The SD of the ammo is usually in the low teens to high single digits. That's across multiple different calibers. I don't pay much attention to any average velocity difference until it consistently exceeds 20 fps.

 

[Veteran]

Yes, that may be the issue.....the ES and SD of the ammo may be higher than the actual resulting effect of the chsnge.....

 

[Veteran]

An example is when my .338 LM was rethreaded for the tuner and new muzzle brake the smith wanted to trim off the old threads and start his own to insure concentricity.

I told him I was worried about losing Muzzle velocity. He said it would be 15 fps or less. I went home and modeled my load in Quick Load with .75 inch shorter bbl.....sure nuff only 15 fps loss in velocity in the model.....about what the ES might be at times...... So yes the effects of a can or no can might be hard to see...

 

[homerthebeeman]

Deep stuff here...

Very deep stuff…and i love it!

 

[Veteran]

Very deep stuff…and i love it!

Yes, I want to know why something works. I think the velocity curves that go flat or down with increase in charge weight are real. I think the ladder tests where there is a sweet spot where vertical dispersion is tight even though charge weight is increasing is real. I think the theory behind barrel harmonics and Newbury OCW test is real.

I think at least right now that the unifying physics behind every one of these methods is rooted in barrel harmonics. These are all valid methods, just from a slightly different angle or approach. They all work or at least get you into the right ball park for fine tuning load development. And harmonics is the only physics or science which I believe can explain why there is not just one sweet spot, one node only but that you can at times find a higher or lower charge weight and velocity range where your rifle groups....Its my working hypothesis for now. I may be proven wrong and if so I will freely admit I went down the wrong alley. So, Im open and exploring this. I want to know why these methods work.

In the case of Newbury OCW, I do not believe there is any open question. It is a fact that this method is the result of barrel harmonics and barrel position at bullet exit. There is no question about this one.

 

[homerthebeeman]

Yes, I want to know why something works. I think the velocity curves that go flat or down with increase in charge weight are real. I think the ladder tests where there is a sweet spot where vertical dispersion is tight even though charge weight is increasing is real. I think the theory behind barrel harmonics and Newbury OCW test is real.

I think at least right now that the unifying physics behind every one of these methods is rooted in barrel harmonics. These are all valid methods, just from a slightly different angle or approach. They all work or at least get you into the right ball park for fine tuning load development. And harmonics is the only physics or science which I believe can explain why there is not just one sweet spot, one node only but that you can at times find a higher or lower charge weight and velocity range where your rifle groups....Its my working hypothesis for now. I may be proven wrong and if so I will freely admit I went down the wrong alley. So, Im open and exploring this. I want to know why these methods work.

In the case of Newbury OCW, I do not believe there is any open question. It is a fact that this method is the result of barrel harmonics and barrel position at bullet exit. There is no question about this one.

Just want to thank you and other on LRH for sharing your years of knowledge.