According to Oehler technicians, the reason for the peculiar secondary pressure spikes with the strain-gauge PSI systems is from the "electrical effects" of the ionized gases from the muzzle blast interacting with nearby connecting cables. They believe that they can reproduce the effect by strategically placing the cables such that this effect occurs, and they can eliminate the secondary spikes by simply moving the cables away from the muzzle blast. In other works, its an artifact created by the "electrical effects" of the ionized gases of the muzzle blast. Interesting idea - any thoughts?

I was over at the mountain molds site. The data he has shows two secondary pressure spikes, the first was clearly before the bullet left the muzzle.

Well then some on here should try to do it
and see if Oehler is right.I don't think that is the source of those spikes that mtngun is showing on his site.And another PT expert told me that he could make spikes at will in a 7.62
Russian by changing to 123 gr bullets(used in AK loadings) and using
different powders, as opposed to regular wt bullets.Don't know if he wants into the argument over this, but he can decide when he reads this thread.
Short light bullets or slippery bullets that start easy are the culprit with the wrong powder--bullet starts too easy, combustion slows, bullet slows, powder gets back up to speed and with bullet slowed, a spike occurs.
Mtngun has set up pads out near muzzle(with
wires run back)
also and recorded the spikes on the same loadings(His slippery bullets) that showed same spikes on sensors on the chamber.And he
has tested other harder to move bullets in same setup and no spikes occurred.

I would think that they(O) would have mentioned such a thing years ago for the benefit of their customers...........Ed.

quote:

Interesting idea - any thoughts

It was one of several ideas we hashed over about a year ago on this topic. As a working Electrical Engineer I can say that it should be easily reproducable, and it isn't. The physics of induced magnetic fields and their effect on nearby conductors is pretty well understood...and the shielding on the strain gauge should block 90+% if it. The 'classic' experiment was (by Denton I think) to move the leads from perpendicular to the muzzle and parallel to the muzzle and verious angles. The plasma (hot combustion gases) and induced magnetic fields should show significant variations in the spikes, and it didn't.

Unfortunately the thread is now lost/scattered in the pre-upgraded world of AR. Maybe someone saved a copy...the makers of the RSI Pressuretrace were involved in several postings...

The electrically induced artifact idea is a nice sophistry, but not the source of the spikes.

The electronic reasons are many, including the fact that the input to the PT is balanced above ground, with a diff amp that would reject such a signal to the tune of 90 dB. That's a whole dang bunch. Besides, have you ever seen any evidence that gunshot produces an electromagnetic pulse?

There are multiple excellent physical evidences against such a notion. One is that Charlie Sisk has now blown the muzzles off three rifles, by deliberately inducing large spikes. Another was already mentioned--I can make them come and go at will, with the same cable, same system, same rifle, just by changing powder charge. With 123 grain bullets in my Finn, I can shoot a charge that causes a small spike, and then go up a couple of grains and pull a whopper. Still another is that the pulse happens before the bullet leaves the muzzle.

Another experiment that has been done is coating the barrel with very brittle insulating material. Where there is strain, it cracks. It cracks nearer the muzzle, at the point where the bullet is when the spike happens. There is now one known case of a varmint rifle that is "ringed" at that point.

There are a lot of ideas floating around, but that is one that doesn't make the cut.

And what must be done is that folks using
this testing and are good at it, find what type of loads do this and get the info out so that people won't load the same and damage
barrels.Denton, do you think this is
a bigger problem, or bigger chance of happening
in 25-35 caliber range, with necked cases as opposed to big bores?Ed.

I wish I had an animation to show this. I've been wondering if the pressure spikes and the blown off barrel ends, are a result of longitudinal wave superposition. The barrel is not very lossy, so it will vibrate for a relatively long time (sort of like a bell ringing). It is possible to have a standing wave, where the sum of the two waves results in a compression (thinning) of the barrel sidewall to the point of failure. High pressure would corespond to thickening of barrel walls.

Now all of this may simply be effecting the peizo transducer, and not be indicative of a real pressure increase. That doesn't mean the pressure doesn't vary due to the reflections, it just means that the transducer may be exagerating by a factor of 2.

I know the progation velocity of a longitudinal wave is about 4.2us/inch. I know the rise time for ignition pressure increase is about 250us. What I don't remember is how to figure out the dominant frequency based on rise time and then relate the wavelength to the physical length of the barrel. Stuff is sortof rusty in my head. Oh well, it's late and nobody pays me to remember this stuff anymore

Denton; The common mode rejection may be 90 db at 60 hertz, but it reduced 20 db per decade of frequency. Rapidly changing waveforms have greatly reduced rejections. In what way is the gage shielded, either electrically of magfnetically.
Good luck!

How often have you ACTUALLY EXPERIENCED a blown-up barrel tip - either in your own guns or seen-it in someone else's gun? In a lifetime of shooting (and being around shooting) I've never experienced it nor heard of it! How often does this occur with the military - folks who fire millions of rounds per year? - essentially never. Yet, you guys "measure" these spikes continually, claiming they can blow the tip of you barrel up. Something is very WRONG here! The secondary spikes must be essentially insignificant. They must be either an ARTIFACT of the system (engineering glitch) or a peculiar barrel harmonic effect - maybe a rebound "stretch/expansion" wave reflecting back into the strain gauge - possibly rebounding back from the action or the distal barrel. The profile of the spikes look much like the primary pressure trace - that is, a reflection.

Ackley.........I agree.

Some of these guys are getting lost in their little world of electronic instumentation and forgetting their logic and common sense .

quote:

Another experiment that has been done is coating the barrel with very brittle insulating material. Where there is strain, it cracks. It cracks nearer the muzzle, at the point where the bullet is when the spike happens.

Denton,

Do you know if that "material" is one of the coatings designed for stress analysis? Stress Coat is one trade name. We've been tossing that idea about over at Mtn. Molds. Thanks.

Forward mounted sensors are able to
pick them up.
Don't seem like there would be
a compression rebound effect there, that
a forward mounted sensor would pick up?

And when these are occurring bullet is moving,
not at rest like at the start of ignition,
so the barrel strength in most guns handle
it ok. It is not like a detonation against a
parked bullet, in the effect
on barrels.So most bareels hold it.So that
is why there is very rare problems.

But loads that might be a problem should be
found out and put out too the reloading,
wildcatting folks so they can stay away
from them.Ed.

Lots of questions... and I've got one foot out the door to go on a business trip.

How many barrel tips do you have to blow off before you decide that something is really happening? Or how many barrels do you have to ring? Not many. We have enough.

The name of the material is Nalco. John Buchanan at Precision Crafted Ammunition is the one who did that experiment.

I haven't experimented with larger and smaller bores... no data yet.

The effect happens predominantly in long barrels, and with light bullets.

Whatever is going on, there is a lot of energy being put into the event, it is happening in the region of the bullet, and we are seeing a remote manifestation of the event, back at the chamber where the gage is. The model that makes the most sense to me at the moment is that somehow we are inducing a momentary stretch in the barrel, which, when it releases, causes a ring wave to propagate down the barrel. You very well might also be seeing superimposed waves, as suggested. That could be it.

We know it happens, we know its real, and we know a few things about it. What we don't have, so far, is a physical model that works.

quote:

or seen-it in someone else's gun?

Yes.

quote:

The effect happens predominantly in long barrels, and with light bullets.

That sounds suspiciously like an oxymoron to me.

Has anyone bothered to ask the question: why did no-one notice this before there was pressure testing equipment? The "ringed" barrels I mean. No-one was concerned until a couple of years ago.

As I wrote a response to one of the principals of the PressureTrace: have a rifle producing the "spikes" or whatever they are, and slowly cut off the end of the barrel closer and closer to the point of the "spike" until you go through it. There are many answers this experiment would give. If it were purely pressure related, the "spike" would go away once the barrel was shortened enough. Vibrational effects due to mechanics (this was tossed about for awhile), would be answered as the "spike" would move as the barrel were shortened. And so on...

As a chemist, the "ionized gases of the muzzle blast" is ridiculous. The solid matter of the nitrocellulose/nitroglycerin composition is plenty sufficiently cooled by the time it reaches the muzzle that there are no longer any free atoms floating about. Only within the actual chemical reaction, i.e. within the chamber and near the chamber would temperatures be sufficiently high enough to allow for free atoms. Once the bonds between the atoms are broken, they very quickly rearrange into compounds again (CO2, N2, H20). The flash you see at the muzzle is high temperature (as compared to the surrounding air), gases cooling, and falling back through energy levels releasing photons.

Another thing to do would be to try same loads creating spikes, in a real heavy bull barrel.
I mean a heavy straight full size barrel blank.
Then "IF" secondary spikes went away, then that would point to compression of waves in the barrel affecting metal expansion the sensors are picking up-----as I think that the loads
couldn't get the heavy barrel to stretch and
compress like light barrels.
Another question has anyone rapped the front of a barrel real sharp with a hammer to see if
the wave however big, generated a spike from
chamber sensor???????Ed.

Secondary "pressure" spikes caused by a harmonic effect (expansion wave) rebounding back into the strain gauge, which I suggested above, seems to have gained a bit of momentum.

As the powder ignites and the bullet travels down the barrel, a pressure bulge is created that must travel in both directions from the chamber - that is, into the tenon of the action as well as along with the bullet down the barrel.

In a sense the pressure bulge would have wave properties, which theoretically could reflect back toward the chamber - its starting point.

Moreover, steel is a very stiff elastic, and thus the wave would travel very quickly. As this wave passed back through the strain gauge a secondary spike might be created. Such waves (pressure bulges traveling as waves) would mimic the primary pressure spikes - that is, the secondary spikes look (apparently in most cases) like smaller primary spikes. A reflected pressure bulge/wave would have diminished intensity. Furthermore, the piezo-electric transducer systems do not record these secondary spikes, because they measure chamber pressure more directly - rather than deformation or stretching of the chamber steel


The timing of the secondary peaks suggests that the waves (traveling as a pressure bulge) may be bouncing back from the action, rather than the barrel; because, the spikes occur before the bullet leaves the barrel.

The ionized gas in the blast seems to have lost "steam" as a potential explanation.

Who knows, just thinking - Regards and safe/happy shooting, AIU

quote:

The flash you see at the muzzle is high temperature (as compared to the surrounding air), gases cooling, and falling back through energy levels releasing photons.

Absolutely correct, according to my understanding. The fire is long out by then, but the gasses are hot enough to glow. You also have some H2 gas as a byproduct, and sometimes you'll see that ignite as it hits the air.

quote:

Another question has anyone rapped the front of a barrel real sharp with a hammer to see if the wave however big, generated a spike from chamber sensor???????

I just don't have the heart to do that with a hammer, but I have done it with a mallet. I have also stuck a firecracker down the muzzle. No effect.

AIU, I think the general area you are going is not far from where I am. If you bulge the barrel within its elastic limit, and then let it snap back, you ought to get a wave propagating up and down the barrel. As noted, it should bounce around quite a bit.

I suggested the following experiment a while back to test the expansion wave theory...but I haven't had the equipment to try it...

Take multiple strain gauges and wire them to a 4-8 chamnnel high speed digital oscilloscope (100 Mhz should be good enough, but faster ones are available). Place the gauges at the chamber, 1/3 length, 2/3 length, and muzzle end of the barrel. Examine the overlaid traces on a 'spiking' load. If it is an expansion wave, it should show a progression/time lag from the origin (theoretically the muzzle) to the chamber end. It should also show some rebound from chamber to muzzle...but possibly very small. In simple terms, the secondary peak would show up at the muzzle gauge first, then the 2/3 gauge, then the 1/3 gauge, then the muzzle.

Simple, right!?!? Now to find a $10000 o-scope and go to the range!

Has anybody using piezo equipment experienced this, or is it specific to pressure trace stuff?

DD, the IMR/Hodgdon experts, who report using a state-of-the-art piezo electric transducer system, claim these secondary spikes do not occur. Hence, the secondary spikes appear limited to the strain-gauge systems.

quote:

Originally posted by Ackley Improved User:
DD, the IMR/Hodgdon experts, who report using a state-of-the-art piezo electric transducer system, claim these secondary spikes do not occur. Hence, the secondary spikes appear limited to the strain-gauge systems.

And that would make since if the strain guage is measuring a longitudinal wave reflection.

But I don't see how the longitudinal wave reflection would result in the end of the barrel thinning to the point where it fails. Unless this only happens with a tapered barrel.

Well then, that certainly clears things up.

Mtngun hammered his barrel today, repeatedly and no trace even at lowest settings, and
I thank him for doing it.

But if the compression wave idea is to be considered, two questions must be figured out.
Why no spikes on all types of loads with
hard, soft, slippery, heavy, light bullets,
in a certain gun..Only some loads.

And secondly loads causing spikes must be tested
in a bull barrel.Where the heft of the metal would affect compression and wave rebound, to see if it makes a difference.If bull barrel
made a difference, then the reflected wave
reinforcing the regular wave idea
has support.If no difference then probably
other idea we mention.

But I think that every load combination in
a certain gun generates waves and reflected waves. In steel the waves travel at 16000
ft per sec I read on other forum.And if they
are responsible for spike reasdings,
And some where
in the curve or cycle of every type of load
wave reinforcement occurs, then all loads
should have secondary spikes. Some where in the cycle as waves move super fast in steel!!
But only some loads have secondary spikes.

I would do heavy barrel test if possible at all.
I have no equipment, no small bore stuff to
work with, and 47 other projects going.
Later I am going to try PT on big bores.Ed.

We need to put one more piece of information into the puzzle.

When Charlie Sisk found his spikes, they appeared on a cleaned barrel, but not on a fouled barrel (IIRC). Why? How does that fit in with the "easily engraved" bullets like cast? FWIW, Dutch.

The fouling created more friction.
So cast bullets engraved harder like jacketed.

Keeping more steady gain in pressure and acceleration, so not too much drop in pressure
allowing bullet acceleration to slow.
If bullet slows I think powder slows and
then powder takes off again and a spike occurs
as bullet has slowed and acceleration has to
be picked up again.

On other forum report of stress paint test
on light and heavy barrels showed stress in both from a spiky load.That points toward
the above idea, not the wave reinforcement idea.

Here is a thought. Say you are comparing easy to engrave and hard to engrave bullets.
Same gun, caliber, etc.
Same wt bullet and same powder.You
use powder that works with hard engraving bullet the best.And you set a
peak pressure limit.So with harder engraving bullet you use less powder, for keeping
under peak limit. Easy to move bullet you put in extra powder, get same peak at start, but bullet jumps say the first 20% of barrel travel
faster than hard engraving bullet, leaving to much pressure off of the burning powder, and powder burn slows, bullet slows, pressure returns, and compared to other bullet you have more powder, so you get a spike.And during
short interval when powder slowed extra gases
were released from powder that where not burned instantly and then when it took off it made
a faster than normal burn, when they caught
up.

Solving it means using a faster powder for the easier engraving bullet.And if it is a
jacketed light bullet you may get your high velocities
ok. Using a cast heavier easy engraving bullet, you may have to settle for less velocity using less powder, which by the way most cast bullet loads are slower than the same wt jacketed ones, as faster powder will raise peak pressures
due to extra wt of bullet...Like a 130
gr jacketed vs a 180 gr cast, in 30 caliber.Ed.

Determine the wave propagation time. The speed in Iron is approx 5100m/s about 16,732 f/sec. So yes absolutely a pressure wave can beat a bullet out of a barrel but that wouldn't be my guess due to not seeing the phenomenon every shot. I would check the installation of the gauge and type of strain bridge being used. Is the wire laminated to the barrel or hanging of the strain gage. A wheatstone bridge is quite an amplifier. Rub the gage with you thumb to see if you get a reading it may just be a poor bond. If its suspected to be a combustion issue the bearing length of the bullet may be an issue. If your using a light bullet with a worn throat I could see a primer sending the bullet down the barrel a ways and pressure building after the engraving pressure increased or changed. Does crimping the bullet in the case have an effect or seating pressure? Are you measuring something that could my have hangfire type symptoms, meaning a real mismatch between primer, powder and bullet. The problem with all this analysis everyone is speculating is you need a position sensor for the bullet to debunk these theories. I think you would be able to wrap a coil around the barrel and detect the bullet passing through it, come on you electrical engineers speak up.

quote:

Originally posted by DemoSam:
Determine the wave propagation time. The speed in Iron is approx 5100m/s about 16,732 f/sec. So yes absolutely a pressure wave can beat a bullet out of a barrel but that wouldn't be my guess due to not seeing the phenomenon every shot. I would check the installation of the gauge and type of strain bridge being used. Is the wire laminated to the barrel or hanging of the strain gage. A wheatstone bridge is quite an amplifier. Rub the gage with you thumb to see if you get a reading it may just be a poor bond. If its suspected to be a combustion issue the bearing length of the bullet may be an issue. If your using a light bullet with a worn throat I could see a primer sending the bullet down the barrel a ways and pressure building after the engraving pressure increased or changed. Does crimping the bullet in the case have an effect or seating pressure? Are you measuring something that could my have hangfire type symptoms, meaning a real mismatch between primer, powder and bullet. The problem with all this analysis everyone is speculating is you need a position sensor for the bullet to debunk these theories. I think you would be able to wrap a coil around the barrel and detect the bullet passing through it, come on you electrical engineers speak up.

I think you'd need a ferous metal to alter the inductance of a wire-wound barrel. Neither copper or lead would do it.

You could just mount your strain guages at 1" intervals along the barrel. I'm not sure about summing the signals though.

Another thought put a load on the barrel vertically or horizontally and see if you get a reading on the strain gauge.

Mtngun has put all types of side strain on the barrel and nothing happened.He beat it with a hammer,Nothing.Others have used stress coating
paints on thick and thin barrels, both show stress where the secondary spike was occuring.
So I think it is a powder,bullet, combustion
issue.Easy to move bullets at the start, with wrong powder.Mtngun has some of his cast 06 bullets oversize enough so that he has to force the bolt hard to chamber a round. The bullets are in the throat tight, and yet he gets spike.
Bullet makeup of his cast 30 calibers is still an easy moving bullet compared to jacketed, even jammed in.All cast bullets are esier to engrave rifling than their same size and weight jacketed coounterparrt.His powder
is about the same as used for a jacket bullet of same weight.Trying to get high velocity.
But bullets jumps out faster at start and
combustion process changes for that wrong
powder,as I described above.When I say wrong
it is in context of--- it may be getting velocity, but it is getting spikes also.

Mtngun used a ball powder W-748 and spikes went away,So I posted this on the thread on his site----
"I like DB ball powders and get best
velocity out of my wildcats with them.Would you please try W-760 and being slower than 748 will allow full loads.If no secondary spikes occur with
760, which I don't think will spike, then I know for sure the reason for the spikes using too slow of tubular

IE,Here is my theory-- DB Ball is degressive burning, by that time in the cycle it has its progressive coating has burnt off, and if slippery bullets jumps too fast and tries to cause a loss of
pressure I think the DB ball will be into the gaining combustion phase, that keeps the pressure
gaining steady and bullet from slowing too much.
And no excess production of unburnt gases at that stage----Stick powder is
progressive much longer in its combustion cycle and even though burning may slow, the
structure of the tubular grains keeps on releasing
gases which when burning gets on the ball again, catches fire, and in tandem with slowed bullet, you have a spike.""

Something to think about.
IE, and a way perhaps to get full
velocity loads, using heavy cast bullets in 06....Ed.

quote:

I think you'd need a ferous metal to alter the inductance of a wire-wound barrel. Neither copper or lead would do it.

Harold Vaughn used the inductance thing by mounting a field coil around the barrel and putting a small rare earth magnet on the nose of the bullet, this to detect core slippage. I assume it would also ID the point in the barrel and/or whatever other data you wanted to at point.

Mountain Gun has made many measurements with strain gages. Some results; Strain gages at the breech measure a different "spike" at the top of the breech and at the bottom. A gage at the muzzle will see breech pressure before the bullet gets to the gage. Some seem to occur after the bullet leaves the muzzle. Tying a weight on the muzzle changes the "pressure spike". For each of these several theories have been posted. Mine is that is it a measurement problem. The strain gage is dumb, it only measures a change in it's length. Anything that varies it's length, or adds an electrical signal into the equipment will come out as "pressure". Why the muzzle brakes blow off some rifles does not have to be this effect.
good luck!

Hawkins-you state that the muzzle sensor picks up breech pressure before bullet gets there. That's wrong.I thought the same until I found out that the machine puts out the same length
timewise trace on all sensors and the spike
the thing picked up made the trace look as
a regular trace from breech sensor only with lower spike.Due to being printed on a trace longer than the actual event.But I found out different, that reading muzzle sensor picks up
is from the bullet passing that point.Ed.

I think you guys are on the right track with the combustion issue. Something similar to detonation spikes in and engine. If its ball powder and a straight wall case or has a shallow taper shoulder. How much unburnt powder will follow the bullet down the barrel only to be ignited by the pressure wave from primary ignition catching up. I wouldn't go with slower buring powder I would lean towards a faster burning extruded powder. Extruded powder will tend to lock in the case better unless the cartridge is straight walled. This is an interesting phenomenon to say the least. I'm still a believer cast bullets belong in pistols or blackpowder rifles due to the problems experienced here. Especially when you get to less than 80% of case capacity. Why are they shooting cast bullets?

Looking at a wave propagating in combustion gas:The reflection coefficient for the muzzle to air interface would be negative. Therefore, since the intial rise in pressure, say from 10Kpsi to 50Kpsi would result in a negative pressure reflection. I.e. it would reduce pressure at the muzzle.

longitudinal wave (think of it as the barrel walls thinning resulting in the barrel elongating) propagating in metal:The reflection coefficient for the muzzle to air interface would be positive. Therefore there would be a large positive (adding to the original) reflection. Esentially doubling the thinning of the barrel walls.

It is important to remember that the combustion gas reflection at the muzzle has nothing to do with the static pressure measured at the muzzle. And a longitudinal wave in metal is trying to lengthen the barrel, not cause to vibrate from side to side. For both cases, the reflection at the muzzle is the incident change (pressure or wall-thinning) that occurred at the chamber.

Now for something different - a theory: We assume that the coefficient of friction for the lead to bore interface is constant. But that might not be the case. The lead might start out shearing (high friction, high resistance) and at a certain velocity, due to frictional heating, transistion do a self-lubricating mode of lead-liquid lead - bore, or a very low coefficient of friction. And the bullet speeds up, or accelerates faster for the given pressure. Back to transmission line theory for a moment: A wave, (This sudden pressure change, due to the rapid acceleration of the bullet), will travel towards the chamber. Meanwhile, the pressure dropped, and if the lead-to-liquid temperature is on the edge, the coefficent of friction may change again and the bullet slow down (but this last part is really a wild theory). Bullet velocity is poportional to gas pressure and inversely poportional to friction

OK, the wave traveling towards the chamber will be reflected only if there is a mismatch in impedance of the medium the wave is propating in. Two cases: (1) Very fast powder. It has turned completely to gas by the time the wave returns. No change in impedance, because the "source" (i.e. the powder) is consumed and cannot react (i.e. burn some more to increase gas volume). (2) Very slow powder. Wave returns and the powder is not yet consumed. The reflected wave is a reduced pressure. The powder burns some more to raise the pressue. The low-to-high pressure change begins traveling back towards the bullet. I believe this is what is referred to as "catch up". Now none of this matters unless the round trip propagation time for the pressure wave is much faster than the movement of the bullet. Sound (pressure waves) propagate at ~1100fps. I know that the velocity is much greater at 40Kpsi, but I don't remember the formula. And I've got to get to work


I don't know the pressure that barrel steel becomes plastic and permanently deforms, but I do know that "ringing" and blown off muzzles are due to exceeding that pressure.

dla-In steel the waves travel at 16000 + fps,
as was posted elsewhere.
If it happens as your theory is explained,
then it is a powder combustion issue,
as a causal factor.IE fast powders don't do it.

As I read your idea the waves relecting are adding to combustion pressure, causing
combustion increases that raise pressure fast against slowed bullet thus causing an actual spike.A true reading...Other wave theorys says that reflected waves overlap and affect sensor to give a false peak reading.Does that comparison of your idea to others sound right?

And I think also, that lead gets a little more slippery with heat. Heat from combustion and
friction.But even lead bullets jammed in tight
in the throat and lands are still more slippery than jacketed with clearance, and not jammed
in. And if weighing the same, knowing
lead bullets move easy, folks try same powder
as used on jacketed, trying for high velocity,
and maybe serious problems with these spikes.Ed.

quote:

Originally posted by hubel458:
And I think also, that lead gets a little more slippery with heat. Heat from combustion and
friction.But even lead bullets jammed in tight
in the throat and lands are still more slippery than jacketed with clearance, and not jammed
in.

I'll post a bit more on this later, but for now I think you are right. An experiment could be done where a cast bullet with a significantly higher melting point is used.

I would suggest trying a moly-coated bullet, but I think that the initial engraving would remove the moly from lead to bore interface at the lands.

The premise of the experiment is that the higher the melting point of the gilding material, the more consistant the coefficient of friction.

Lubricating oils have a maximum shear rate beyond which they stop acting as a lubricant. So it is possible that oiling a barrel could make the problem worse.

The spike you are seeing is not related to stress wave propogation. Due to the speed of a stress wave propogating thru a barrel your going to see more than on spike in your data if you were measuring such. And you will see it on every shot. Not just one. Someone mentioned double base powder. At the right temp and pressure it will detonate. I believe a certain famous bomber proved that. Have done FEA analysis on barrels I can tell you most contours will not take a pressure equivalent to the peak chamber pressure over its entire length without yielding.

has anyone considered the rifling stripped from the lead bullet in such an application. Were the barrels excessively lead fouled? It would be interesting to actually recover the bullets.

I use lead bullets surrounded by copper jackets - like virtually everyone else these days, especially those buying strain-gauge systems. Hence, how would lead pealing off the bullet be relevent? I'm beginning to wish I hadn't started this thread.