I went to the website spoken of and saw the pix of the shortening barrel experiment. I wanted to copy the images, but when I went back there, I could not find them. It would be most instrumental were they shown.

There is no "secondary pressure wave", no "mini-see", no vooddo, just an artifact of the electronics and/or mechanical effects. The bullet is in a barrel only 1.04 to 1.07 milliseconds (from Hatcher and 24" 30'06), we see what is to be expected using fast and slow powders, slow lock timed rifles and fast lock time rifles, heavy slow projectiles with light fast projectiles. Long barrels and short barrels, target rifles and miltary rifles. These can be seen from the initial pressure curves and the timing of said curves. As the shortening barrel experiment (which I stated need to be done right after all this stuff came out), has demonstrated, it is not pressure related, as the "peak" moves back towards the muzzle (timing!) as the barrel is shortened. It is an artifact.







Sometimes the phenomenom is exagerated and sometimes it is subtle, but it is always there. So put away the tin-foil hats and go out and enjoy your Pressure Trace equipment. I do, the first pix are of my Argentine with 27" Lilja barrel.

quote:

If the gage is on the top of the barrel recoil will push the receiver back and up. This bends the barrel down

I don`t follow this.
Isn`t the recoil at 180 deg to the bullets base -equal and opposit- and the reason for muzzle climb due to the angle of the stock to the barrel? The pressure on the barrel walls being equal won`t result in one moveing or bending away from the other unless there is a uneven release of pressure in the other direction or a weak spot in the barrel.

I understand a vibration traveling in the barrel but don`t see haw a reciever can do much more then amplify / dampen it from one end. Bullet torque might do it though.......

Nitroman, I believe the bullet is exiting after the second rise starts. This is a trace of a 270Win 130 Hornady over R22. Note the "tic marks" on top of the trace rise, that`s the point of bullet exit as determind by the Pressure Trace unit useing the velocity from my Pact.


You show the same tics on the trace for your 150gr GK in the 30-06, it`s after the mark you point to stateing bullet exit.

NM-- You got exit time wrong. Tics tell when
the PT thinks bullets are exiting.On those loads with that trace
try a ball powder. Then the second spike will probably go away. And ball has more muzzle blast!! You can call them an artifact, but if you cranked up those spiky loads, your
muzzle might be an artifact.Try a full
load of AA8700 or AA Magpro even better.

Varmint Al--Welcome--Site for popenmann or
mtngun on his forum is www.mountainmolds.com
Ed.

Nope.

You are not considering what has been done. As I wrote before, if it were related to pressure, cutting the barrel shorter and shorter, you would be able to see the trace end. Sooner and sooner, as a relation to the shorter barrel.

The "peak" is stated (if it were pressure related), to occur just prior to bullet exit. This is assumed to be a combination of bullet, barrel length and powder used. Ok. Now, if you make the barrel shorter, the bullet exits sooner. The bullet exiting sooner would have no effect on what is happening prior to it exiting. You would see the the "peak" being sliced off (to use a phrase), as the bullet exits sooner.

When the fellow started chopping off his barrel, the "peak" simply moved. Each time he chopped off a bit of his tube.

"Blowing off the muzzle" of a rifle can be done, if you have a bore obstruction or the barrel is thinned at that point. The idea that it can be made to happen on command by using a certain combo of powder and bullets is...being polite...ridiculous.

Hasn't anyone wondered why no-one, ever, anywhere in the world, ever noticed this phantom "peak". Not governments, not genuine professional ballistics labs. No-one? Just now with this particular type of equipment?

Sisk made the peak go away by shortening barrel because Mini SEE or whatever started down barrel
due to the fast jump of light jacketed bullets,
at the instant of ignition and center of mass of gases and powders were down the barrel a ways.

Popenmann or mtngun on his own forum, cut barrel and spiky loads still gave spike, but his heavy cast bullets started hard, then jumped ahead fast, and I think the Mini SEE or whatever started near chamber so cutting barrel had no effect.But he changed to ball powder that operated a little different and spikes went away.Even though the hard to start heavy cast bullets made initial peak pressure little earlier than if a jacketed bullet of same weight was used with ball powder.

Some folks in the business noticed it.They set their machines so as not to pick it. Thus making all this wonderful discussion that gets
my post count up.Also did someone in the
business tell you that the bullet exited
at the point you told us?? If so I want to
know WHO....Ed.

I believe the exit marks shown by PT are based on some assumptions the PT must make regarding bullet drag, etc. I recall the calculations use the area under the pressure curve. I'm not convinced the bullet exit points as marked by PT are accurate.

Nitroman: That said, I believe an older, related thread mentioned a fellow at a ballistics lab had used a radar setup to verify the 2nd peak is coming with the bullet still in the barrel. Also, it has been posted here that piezo rigs may be seeing the same secondary rises in pressure, but this seems to still be in the category of rumor at this point.

(I have not theory as to what's causing all this; just reporting what others have said.)

quote:

trace of a 270Win 130 Hornady over R22.

Ol' Joe, if you could give me the dimensions of the 270 Win barrel, I could do a 3-D modal analysis of it to find the mode shapes and frequencies. It looks like the second pulse has a 1/2 wave of about 0.3 ms and that would correspond to a frequency of about 1670 Hz. I could see what mode is close to that frequencies.

For the dimensions, I would need the diameters at say every 3 or 4 inches along the barrel, its length, and its material. Also, was the barrel free floated? It wouldn't hurt to put some numbers with some of the theories.

Can you answer why the pressure trace starts at 11 KSI at time zero? That looks a bit strange. Was some early data lost?

Asdf--I don't think PT gets exit time right either.IT SETS IT TOO EARLY..This is based on
a lot of complicated math we did 50 years ago
about pressure curves and recoil, that if our interpretations of data we had at the time was correct barrel time was longer than
previusly thought......IE, Early in
this century estimates of barrel time were too fast. And someone saying spike is occurring
with bullet out of barrel, doesn't jib with
mtnguns muzzle sensor picking up a bullet going by it with the high spike right behind it.Ed.

The bullet exit tics will never be extremely accurate, because you never know the exact friction between bullet and barrel. However, it is well established that whatever event we are seeing happens before bullet exits. That was done at PCA, using Nalco varnish to detect the barrel strain, about 3" from the muzzle.

As to whether the pulse goes away when the barrel is shortened, we have an equivocal result. One experimenter found it did, while another found it did not. Both are credible. Until that is resolved, it is highly improper to flatly state whether the pulse does or does not go away with a shortened barrel.

The apparent decrease in pressure simply cannot physically happen, yet is totally consistent with what I have observed on my PT. So one possible explanation is some kind of event that acts a bit like a partial bockage of the barrel. That will momentarily slightly stretch, then release the bore. This will launch a soliton ring wave, that will propagate in both directions, and which will reflect off the muzzle as well.

The idea that such a event is unreal is in direct contradiction to the evidence of three rifles with three blown barrels, and a fourth that is ringed. That we know of. So far.
Charlie Sisk seems to have the ability to blow off muzzles at will.

There is nothing in the PT that is smart enough to get confused enough to electronically create such an event. The signal chain is a simple, incredibly linear instrumentation amplifier, which cannot create such an artifact, and a simple 8 bit A/D converter which is also unable to create such a thing. Nor can any combination of the two create such a thing.

This event has indeed been observed by others. A technician at White Labs has stated that the commercial Oehler systems simply cut off the trace when a sustained decline in pressure is detected. That's extra circuitry, which has no function, unless that system also responds to the pulse. The Fabrique Scientific pressure system flatly states in the manual that steps were taken to suppress what they assumed to be "barrel vibrations". This is nothing new. It is just the first time a lot of people have seen it.

Several posts back, asdf gave the first explanation of a longitudinal pressure wave that I find plausible. Perhaps it has something to do with that, but I can't see anything out of that except a longitudinal wave, which the strain gage will ignore.

If the secondary spike phenomenon is caused by a peculiar barrel/action, hormonic/pressure wave effect, then it doesn't matter when the bullet leaves the barrel - the effect could happen after the bullet leaves the barrel. To me, it seems more probable to occur after the bullet leaves the barrel anyway.

Varmint Al you have a PM

"The idea that such a event is unreal is in direct contradiction to the evidence of three rifles with three blown barrels, and a fourth that is ringed. That we know of. So far.
Charlie Sisk seems to have the ability to blow off muzzles at will."

This is the kind of thing you guys are taking as Jesus' gospel. Haven't any of you bothered to consider, of all the trilliuons of rounds fired since smokeless powder became available, this is the only guy who can do this? HELLOOOOOOO!!!! Anybody home?

Ed Hubel, I am extremely offended by your remark. But hey, what do I know? I only spent 5 years getting a B.S. in chemistry and molecular biology, waiting on my M.S. in environmental toxicology because my committee is slow to get going on my thesis.
My experiences began with fireworks and high explosives starting after my dad began using DuPont 50-50 Red Cross Extra straight nitroglycerin dynamite on the farm back inn 1968. I was making my own cannon crackers (9"x2"), when I was 11 years old after I found his copies of Weingarts Pyrotechnics, and Davis' Chemistry of Powder And Explosives. My current interests are high explosives and thier effects and properties, and chemical weapons. I am a chemist, this is what I am interested in. This doesn't mean I am any smarter than anyone else Ed, quite the contrary, I know full well there are plenty of people with more smarts, it only means I can look at some graphs and derive what they tell me. I can also differentiate between bullshit and reality. So excuse the fuck out of me.

quote:

Several posts back, asdf gave the first explanation of ...

Sorry, someone else deserves the credit; it wasn't me -- I'm utterly befuddled by this.

Nitroman, hang in there friend, your knowledge is certainly an asset here.

NM- Didn't intend to offend friend, but it is
little upsetting; that bad info is out and around the shooting fraternity,
about when bullets leave the barrel in relationship to those traces. That isn't fair to next guy who has problems, thinking he can ignore traces printed out like that.And I
sure in hell don't want you to ignore them
because of wrong info. Been through the
math,physics, chemistry bit myself and studied
ballistics before and during that college
time.If there is industry folks pushing the
idea that all extra spikes are after
bullet exits barrel or that like some were told it is electrical by one of the companies, we should know, and get out right info.That is why I asked. No offense intended.And please check
on a different load.Ed.

PS--NM,I really, really wish you were right about exit time for bullets,
for as a wildcatter going with designs that
are different it would take the worry factor out of what I am doing on some of my stuff.Ed

I have calculated the first 10 Mode shapes and frequencies for the 270 Win barrel. The mode with the frequency closest to that of the second pressure pulse is a torsion mode. Here is an animated view of that mode.


You can view the other mode shapes and frequencies here: http://www.varmintal.com/270win.htm

This might have asked more questions than it has answered.

I do have a question. I assume all of the pressure measurements were made over the chamber. Has anyone tried putting the strain gauge about 3" back from the muzzle to verify if the high pressure does occur there?

Good Hunting... from Varmint Al

quote:

This is the kind of thing you guys are taking as Jesus' gospel. Haven't any of you bothered to consider, of all the trilliuons of rounds fired since smokeless powder became available, this is the only guy who can do this? HELLOOOOOOO!!!! Anybody home?

If you will send me your favorite rifle, with barrel length greater than 24", I will happily test your belief for you, and then return your rifle to you.

There is no evidence that Charlie is the only person do to this. In fact, a friend of Jim Ristow has pressed a rifle almost to failure, producing permanenet barrel rings.

In Charlie's case, he deliberately increased the secondary pulse, step by step, until he blew the muzzle off. Three times, two different rifles. So he has not only done the experiment, he has correlated the outcome with the secondary spikes, shown that the muzzle blow up happens when they are present and very strong, and does not happen when they are small, and he has replicated the experiment.

You also ignore the physical evidence from Precision Crafted Ammunition, which demonstrated very high local, outward strain on the barrel, when the pulses occur, at pretty much the point that PT predicts the event to be.

That's three different sources demonstrating, by different methods, very high strain a few inches short of the muzzle.

'Splain me that.

Varmint Al--Yes, popenmann or mtngun as he is known on his site, put a sensor on muzzle and picked up the secondary peak.His machine printed out a trace 1.5 m-sec long and the spike was at the immediate start of trace. With the pressure way up high right behind bullet when it went by the sensor..Ed.

quote:

Originally posted by Varmint Al:
I have calculated the first 10 Mode shapes and frequencies for the 270 Win barrel.

First of all, a big thank you for modeling this!

A couple of questions:

1. How did you excite this? I.e. what was your stimulous?
   
2. Any idea what the relative energy for each fo the modes?
   
3. Assuming that the stimulous was a uniform, radial pressure applied inside the breach end, how did the bending moments appear?
   

The Questions:
1. How did you excite this? I.E. what was your stimulus?
2. Any idea what the relative energy for each of the modes?
3. Assuming that the stimulus was a uniform, radial pressure applied inside the breach end, how did the bending moments appear?


1. There is no excitation of the FEA model. The FEA code calculates the mode frequencies and shapes mathematically. All that is needed is to solve for the eigenvalues of the stiffness and mass matrixes. These solutions give the mode shapes and frequencies. Modal Analysis determines the “natural†response of the structure.

2. The calculation does not determine the energy partitioning into each of the modes. However some of the modes would be excited more than others. The first bending mode is excited in a rifle because the CG of the rifle is usually below the axis of the barrel and upon firing and while the bullet is till in the barrel, there is a rotation about the CG that would tend to bend the barrel in both modes 1 and 2. The pressure in the chamber and the spin up of the bullet would excite the Mode 5 torsion /breathing deformations.

3. NA

I can't think of an easy way to visualize the matrix solution. Before computer simulations natural frequencies and mode shapes were found by vibration testing. Here is a pretty good explanation of the process: http://macl.caeds.eng.uml.edu/macl-pa/modes/modal2.html

Here is another page that give some information: http://www.modalanalysis.com/

Good Hunting… from Varmint Al