Thanks for the suggestion.

I don't know what temperature is required to strip atoms in CO2, but other inert gasses are cheap enough that it is less work to go get a bottle of one of those than it is to look up the data. Besides, you can fill the bag more quickly...

Ackley Improved,
I am using some of the same cases since I bought the gun about 6 years ago, they may have been reloaded 20 - 30 times, mostly with full throttle cast loads and 4350 which I now know has the big secondary spike. The pockets are still tight and I have never had to trim cases except for the initial squaring up. I have never had a case failure other than the occasional split mouth due to belling the mouth for cast bullets.

To my knowledge, no one has reported case damage or action damage due to secondary spikes. The only reported problem has been to the barrel, near the muzzle.

If you place a partial obstruction in the barrel near the muzzle, what kind of pressure trace will result? Will a copper crusher detect a spike when the bullet hits the obstruction? Will a piezo? Will it cause the action to blow up or the primer pockets to loosen? How about someone (other than me ) go do the experiment on a cheap milsurp rifle and find out? Dr. Mann experimented with partial obstructions, and the only problem he encountered was ...... a ringed barrel. If a partial obstruction at the muzzle can ring the barrel without causing the brass to fail, or without causing unusual piezo or CUP readings, then is it possible that our mystery spike can cause barrel damage without registering a problem at the breech end, except on our stretchy, uncalibrated, unreliable, hypersensitive Pressure Trace?

Mike375, yes, fillers were blamed for the rings in the old days, and the rings were usually located near the chamber throat, so that may be a completely different issue -- though it still begs the question of how a pressure ring is formed, and there may be similarities. I haven't traced fillers yet so who knows what we will find But there was also talk of problems with slow powders. Col. Harrison suggested using a duplex charge of Unique or Herco to get good ignition with 4831. About a year ago, wasn't there a lively debate on this forum about erratic pressures with one of the surplus 50 BMG powders that some people were using with cast bullets?

I could throw out some other wild ideas, but I'd rather be at the range doing experiments. Unfortunately, I have to do income taxes instead

If we look at a brass case as a crush cylinder,we run into the problems of the crusher measuring pressure,duration will show more sign than short peaks.

My question is : Why would a load of Varget not produce SPS, whereas a load of RL-22 would in a 338WM?

Ackley Improved User has a good point concerning what the big labs see using their piezo rigs. Along these lines, one logical place to phone would be Oehler, since they supply both piezo and strain gauge, and see what they have to say. I have to believe they have already looked into this.

John Barsness reports seeing these secondary spikes with strain gauges but not on the piezo rig he has access to. He wonders if the piezo rig would see a secondary spike lower in amplitude than the first spike, since the cartridge case might not relax fast enough to record a second deflection. OK, I think that theory pretty lame, and he admits it is, but he feels there may be something to this secondary spike thing. One way to test his theory would be to put the piezo at the case mouth instead of along the case body. Has anyone seen the piezo traces from a CIP style test? I recall they measure at the case mouth.

Interesting topic...

quote:

Originally posted by downwindtracker2:
My question is : Why would a load of Varget not produce SPS, whereas a load of RL-22 would in a 338WM?

Because the Varget is totally or nearly consumed by the time the bullet enters the "problem" zone???? Therefore it cannot re-ignite???

(Quickload shows powders like Varget are consumed after only 8 or so inches of bullet travel, depending on the load, and after that, the only thing pushing on the bullet is the compressed gas trapped in the barrel, much like an air rifle).

Because Varget burns OK at moderate pressures, whereas the problem powders may burn erratically if pressure drops below a certain level?????

I've used words like "burn", "re-ignite" and "the flame goes out" loosely, but the actual phenomena may not be a "burn." Even Bullseye does not create an instantaneous pressure spike when it burns. We could be seeing a detonation, a collision (a pressure wave colliding with the bullet base), or a reflected pressure wave.

So many possibilities .......

popenmann, your strain gauge is situated on the chamber - putatively measuring (indirectly) internal pressure at that point. If your instument is showing a massive spike (sometimes to 107,000 psi plus) then that much "internal pressure" has to be occurring at that point - that is, in the chamber. Also, because the bullet has traveled and is located in the distal barrel, the implication is that the strain gauge is estimating pressure that must be uniformly distributed throughout the length of the barrel traveled by the bullet. The bottomline is that the case had to be exposed to these massive pressures just like the rest of the barrel.

But, you report that you're reloading your cases multiple times - even 10 to 20 times - and, they show absolutely no pressure signs. Brass is not immune to pressures of 107,000 psi plus - cases exposed to such high pressures should be unusable, stuck in the chamber, and/or the primer pockets totally destroyed - BUT THAT IS NOT HAPPENING! The only conclusion is that the massive secondary spikes in "pressure" are not happening and that these peculiar secondary massive "pressure" traces are technical artifacts of the system. Moreover, it hard for me to believe the distal barrel could withstand such massive pressures. The action and chamber might withstand pressures over 107,000 psi plus, but not the thinly metalled distal barrel.

THE INESCAPABLE CONCLUSION FROM YOUR DATA IS THAT THE SYSTEM YOU'RE USING HAS SOME MAJOR TECHNICAL PROBLEMS THAT MUST BE WORKED OUT BEFORE YOU CAN GET RELIABLE DATA.

AIU...

Good job! You have now graduated from opinion, the lowest grade of information, to the middle grade, analysis of data. I think you're doing better.

There are a couple of problems with your analysis, though.

First, you have not accounted for all known data. There is the issue of Charlie Sisk's barrel tip being blown off twice, and a varmint rifle owned by Jim Ristow with an expansion rings near the end of the barrel. In the face of that, it is not proper to assume that the secondary spike is not real pressure.

Second, you have not accounted for the data (remember, data trumps analysis) that says that the strain gage system is highly repeatable, at least on a par with piezoelectric systems. The single most key figure of merit for a measurement system is repeatability.

I suppose that it is possible to measure true blood pressure by opening the patient up, and hooking a manometer directly into his aorta. Fortunately, doctors have a pressure cuff that measures it indirectly, by measuring the ability of blood in the arm to swell the mass of the arm in opposition to air pressure.

Pressure cuffs manifestly work.

Strain gages manifestly work.

All arguments that they cannot work fail in the face of the fact that they do.

Do I find the secondary spike troublesome? You bet. And the fact that the brass isn't smashed beyond recognition is a real issue. I don't know the answer to that. There is always more that we don't know that we do know. Fortunately, there are a few things that we do know.

AIU,the duration of the load on the brass is so short that the brass doesn't deform.That just common sense.This was a complaint about the old copper crusher,too.My opinion on SPS,if the brass isn't harmed,maybe the rifle isn't as well.They have been burning 4831 for almost 60 years ,now.

Her is some more thoughts on them;
[URLhttp://www.24hourcampfire.com/ubbthreads/showflat.php/Cat/0/Number/457413/an/0/page/0/gonew/1#UNREAD]other thoughts[/URL]

DWT, at 107,000 psi plus the brass will respond - if it doesn't, it means the pressure never reached those heights. The secondary massive pressure spikes have to be an technical artifact - possibly some peculiar "rebound" effect as pressure returns to normal. Remember the ballistic engineers at IMR/Hodgdon don't record these secondary spikes with the piezo electric system - neither does the case, the best record of what happened inside the chamber.

P.S. Blood pressure cuffs are notoriously inaccurate in FAT people.

I am definately interested in what a multiple gage recorder would have to tell us about what is happening at various positions on the barrel.


Fortunately, the end of the barrel does not get ringed or blown off often enough to motivate the major balistics labs to investigate this phenomenon with all the instruments that modern science could bring to bear.

It occurs to me that if we had the instruments to record it we might see a standing wave propagated in the barrel, coupled with reflected sonic effects in the gases in the barrel.

Often poorly understood phenomenon of this nature are attributed to several sources as we finally gain a thorough knowledge of them. There are so many dynamics at work in the process of internal balistics, and the events occur so quickly, that I seriously doubt we will gain a complete understanding of the process during any of our lifetimes.

I can imagine a ring type wave of expansion being propagated at the chamber, traveling to the muzzle, then returning to the chamber.

Or a vibratory wave could be traveling to the muzzle and returning. If such were the case, two strain gages mounted at opposite ends of a chamber diameter would give different values. Or more accurate yet would be three gages mounted at 120 degrees around the circumference of the chamber.

Even if a strain gage is occasionally subject to some little understood noise patterns (we still do not know for sure if these secondary spikes are real data), It is less so than any other method of determining chamber pressure available to the hobbyist of less than multimillionaire status. Thus it is still the most accurate and repeatable system available to most of us.
It is of even better use if its use is coordinated with observations of MV and fired brass. A wise man takes into account all data available to him, and considers the validity of each.

First, I am not a ballistician, nor a physicist, nor a a chemist, nor any other kind of scientist it would take to figure this out. Nor do I play one on TV. There are a few things that I think I know though. First, the bullet is travelling fastest at the highest pressure -- while it is still in the barrel. Next, as pressure drops, the bullet decelerates. Third, if there is any powder left at that point, crushed by pressure/heat, it might stop burning as pressure drops. Fourth, I was under the impression that white powder had enough oxygen on board to sustain a complete burn chemically.

Could it be that a decerating bullet, pressure dropping, the fire goes out actually acts as an obstruction for the gas column to catch up too, raise pressure, reignite the powder and give the slowing bullet another BIG push. Just a poor ole country boy thinkin' about things. sundog

naw. prolly way to simple...

New hypothesis... and I think it accounts for most all the data.

The oxygen depleted, incandescent gasses exit right behind the bullet. The gasses mix with air, and are pulled a little way back into the barrel, by the partial vacuum that is pulled by their rapid exit, and the hydrogen and oxgen explode in the barrel. This exerts outward pressure on the barrel for a very short time. As the barrel stretches and snaps back, it launches a single pulse wave in the steel, which propagates toward the muzzle and toward the breach. When it reaches the strain gage, it produces the pulse we see.

A pulse like that does not represent real pressure at the gage, which explains why the brass isn't mangled, but it is a real wave in the steel, from real, fast pressre near the end of the barrel.

The electronics in the PT are not designed to show actions that put the gage into compression, so we can't see the whole wave, just the tension portion.

That explains Charlie Sisk's muzzle, and Jim Ristow's ringed varminter. It explains why we see the pulse. It explains why we do not see mangled brass. It explains why it happens more in longer barrels. The remaining issue is that it appears to sometimes happen before bullet exits, so that is something still to be explained. Perhaps the exit marker is off??

Of course, until someone puts some observational data behind it, it is just a hypothesis, but I like it better than others I have seen.

BTW, the Fabrique originally was able to see these pulses, but the designer fixed it so the user does not. The PT unit sees them, as we know. The Oehler unit also sees them.

Denton, your hypothesis doesn't answer the Varget vs RL-22.Or the slow dirty barrel.The big muzzle flash powders should have greater peaks.My favourite, N-560 is not the powder for drought conditions.

As regards "instrumentation problems", the bending moment on the barrel could also give such an output. The recoil impulse causes the receiver to rise. This gives a downward flex to the barrel. Two gages on oposite sides of the barrel would be needed to measure this. It is hard to believe the data is "real".
Great information on these postings, tou never know it all.
Good luck!

quote:

Originally posted by popenmann:

quote:

Originally posted by ASS_CLOWN:
popenmann,

What is the trace like if you place the strain gage 4" rearward of the muzzle? How about 6" back from the muzzle, then try 8" back? The results may be surprising.

ASS_CLOWN

I haven't tried it myself, but vaguely remember reading about someone trying it, and confirming the existance of the spike. I've got a bunch of gages on order, so maybe I will be able to try it later. Ideally, you'd want to be able to read all the gages at once and synchronize the output, which I am not equipped to do.

I think it's quite possible you're equipped. Couldn't you not connect a chain of strian gauges glued all the way down the barrel in series?

The first gauge to stretch would be over the chamber. The increased resistance shows up as pressure on the software's graph. The next gauge down the line wouldn't stretch until the bullet passed, and the passing of the bullet would look like a sudden step up in pressure on the graph. As the bullet passed each strain gauge, the resistance of the whole series of gauges would go up in steps, and the trace you would record would look like a staircase.

Of course, you may or may not be able to make use of the recorded pressures, but you would be able to measure the position of the bullet versus time and wouldn't need an expensive high-speed x-ray movie camera to do it.

I guess all the gauges could be connected in parallel and hooked up to the same Pressure Trace module or recording oscilloscope or whatever, and you would also see step changes in the resistance. Maybe the smaller change in overall resistance would help you keep the whole recorded resistance versus time trace on a meanigful scale that you (not I) could interpret.

Would this help you detect or understand pressure spikes?

H. C.

I think we have an answer... or at least a better hypothesis than the one I put forward. I received this from the person who designed the PressureTrace:

quote:

Denton,

I went part way down that road way back at the beginning since a moving plasma can generate an electric field. I determined at the time that the electric field created would not be nearly big enough to cause the effect we were seeing. Since the secondary pulses I was seeing were happening before the bullet exited the barrel, I eliminated what you are thinking of from further consideration. I had to go with something that could cause the problem in all cases not just some subset.

And we do see "mangled" brass. The brass from my 243 AI was blown out and ruined (loose primer pocket) by the huge pressure pulse with just one shot.

A Chemistry Explanation

I guess you didn't get the information from the ammo manufacturer in Virginia. Whoops. He was a chemist who got sick of the rat race. Now he makes custom ammunition for people who don't want to take the time themselves. Apparently it's fairly lucrative.

Anyway. He wanted to understand secondary pulses. He set up a microwave radar reflected down into the barrel. When he shot he was able to determine bullet position during the entire event. The bullet then went through the reflector.

He correlated the data and found where the bullet was when the secondary pulse occurred. He drilled a hole in the barrel behind the bullet position and sampled the gasses in the barrel during the secondary pulse with a gas chromatograph.

I don't have the exact gas breakdown. He may have sent it to Jim. (We had hoped to make contact with him at the SHOT show but it didn't work out.) I do remember that the gasses in the barrel when the secondary pulse is just starting has a nitroglycerine content 300% above what it started with. It's this atmosphere that is about to blow up and create the secondary pulse.

He found definite correlations between the type of powder used and the volumes of the explosive gasses. Ball powder was the worst.

He believes that he can explain secondary pulses strictly from a standpoint of chemistry. What he says dovetails nicely with the Catch Up theory.

Given his mangled brass, Charlie Sisk's blown off muzzle (twice), and Jim Ristow's ringed barrel, I think it is safe to say the following--

1. The secondary spikes are real events that are a real hazard.

2. There is a very plausible explanation for them, based on a serious investigation.

3. A few people detected them before PressureTraces became so common, but nobody took them seriously or explained them. So it almost counts as a new discovery.

Many years ago Dupont loading data tables consisted of listing all of their powders for all of the calibres and resulting pressures.

So at one end they had to top loads with 4227 in the 264 with 140 grain bullets and at the other end a case full of IMR 483 with the 458, 308 and 222 etc.

Those loads would have been based on the copper crusher which should show the higher pressure obtained while the bullet was in the barrel.

It is reasonable to assume that they never saw the 100,000 pressure spike readings with powders that were way too slow for some of the calibres.

The other query I have is that with calibres with large expansion rations such as the 30/06 and I think the 7.62 X 39 was mentioned....if such a calibre was plugged at the end of the barrel, but with no bullet, what is the maximum pressure that that could occur. I think I remember reading quite some time ago that if the powders we use were ignited in a container with no room for the gases to expand the maximum pressure that would be reached would be 250,000 psi.

Some of the users on the thread with the pressure tracing equipment have mentioned about going back and dupicating loads that produced over a 100,000 pressure spike. Have the users been prepared to do this because they do not fully believe the readings reflect reality.

Lastky, for those of you that have experimented with the pressure tracing an differnt loads what are you thoughts on these type of loads:

1) 378 Wby loaded with around 85 grains of the 4964/Varget burn rate which usually gives 2600 plu with 270 grain 375 bullets and is about 10 grains below a maximum laod with such powders.

2) 460 Wby also with about 85 grains of the 4064/Varget and 500 grain bullets which gives just over 2000 f/s and such a load is about 20 grains below maximum.

Note: No fillers used in the loads.

I have used these type of load in two prevously owned 378s and two previously owned 460s and with out problems....at least observable problems

However, since I have a pair of 378s and a pair of 460s coming from the Wby custom shop I am not overly keen to ring barrels etc.

Any thoughts on those type of loads and simiar loads with powders in the 3031 burn rate.

I have used, but not that often, reduced loads by using powders too slow and in the 460. A friend of mine regularly uses 105 grains of H4350 for 500 grains in the 460 with 500 grain Hornadys and that is about 15 grains under a top load. His load is similar in principle to most of the loads being used in the 416 Rigby to give 2300 or so with 400 grain bullets.

I am not convinced of the secondary explosing factor with reduced loads of slow powders in big cases with small bores. However, it is at the back of mind and I would not use 85 grains of H4350 with 150 grain bullets in a 30/378, which pressure wise is similar to 85 grains of Varget/4064 with 270 grainers in the 30/378.

So in summary, from the experiments you have done what type of loads would you avoid and especially in relation to the type of reduced loads I mentioned in the 378 and 460.

Mike

I once ran out of 4895 for my '06 match rifle, and subsituted AA-2495 (46grs./168 bullet). The rifle shot well for 60 rounds, but here is what happened every third shot or so:
1.Huge fireballs were blowing out the muzzel (noted by range officer)
2.Brass comeing out of the chamber was too hot to touch.
3. Brass comeing out of the chamber had the neck slightly sized down (and bullet would not re-enter).
4. The barrel was heavily coppered. It took sereral days and half a bottle of Sweet's to get it out.

I concluded that I was getting a secondary burn down the barrel. The same powder worked great in a .308.

quote:

when the secondary pulse is just starting has a nitroglycerine content 300% above what it started with.

Denton, does this mean the secondary pulse is never seen with single base powders?

Don't know yet.

Well, maybe we do. I was getting some very distinct secondary spikes with Varget, a 27" barrel, and SKS 123 grain bullets in a 7.62x54R. So the proposed model does not yet explain everything. Varget does not contain nitroglycerin, but it does contain 2,4-dinitrotoluene, and I have no idea how that might behave, or what compounds it might produce in a cooker.

As you increase a load, you first see a little flat spot in the decaying pressure. Then, as you go up a bit, you see a little 1 cycle sine wave in the decay. As you go up more, the positive portion of the sine wave grows, much more quickly than primary peak does. Eventually, it maxes out the measurement system.

Hmmmm.... some of that argues for some kind of wave propagating through the steel. The wave is real, and the gage can "see" it, but it does not necessarily represent pressure at the chamber.... heckifino.

Denton, forgive me for getting too detailed...but curiosity is a major part of my nature!

Did your friend's experiment include loads that didn't show spikes? IOW, was the nitroglycerin content the only difference noted between loads with secondary spikes and those without? With the same, or VERY similar powders...or better yet the same powder and heavier bullet that didn't show 2nd spikes?

What kind of gas sampling system can measure nitroglycerin content at those kinds of temperatures and pressures? I don't have tables with me at home (vacation today), but I suspect the autoignition temperature of nitroglycerin is well below what is found in the average rifle.


Is this experimental data available online?

The explanation sounds good on the surface, if we can find a way for NG to not autocombust until reaching the later stages of the barrel...maybe still contained in some unburned powder kernals...maybe as a byproduct of DNT or nitrocellulose combustion?

Feel free to PM me if you like...

CDH, I've posted just about all that I know about it. I may be able to get some direct info from the guy who did the experiment, and I will ask.

I've seen the spikes with Varget, and I don't know diddly about 2,4-dinitrotoluene, which is in Varget. You get hanging dinitro and trinitro onto toluene or an alcohol (like glycerin), and it just has to be in the same class of chemicals as nitroglycerin... but I don't have a clue how that would behave. So does that count as a double base powder???

Wonder if I would see them with Accurate 2015, which I have on hand, and which is definitely single base??

This is one of those aggravating details the just bugs the bejabbers out of me. And you would certainly think that NG would explode at the temperatures and pressures in a barrel, wouldn't you?

Denton has anyone you know of looked at how long the barrels are when these secondary spikes show? Can you see it in short 20-22" barrel or just the longer ones? Everything I seem to hear on this claims its a longer barrel occurance, something we find in varmite and magnum rifles with long tubes for peak velocities.

Ol' Joe
I have that 25" tube on mine, if you want to experament. Just remember that we never ran a throater into it, so it is very short to the lands (Don't try using a 220 RN in it, you'll never get the bolt closed).

quote:

I don't know diddly about 2,4-dinitrotoluene

IIRC, DNT is a deterrant. What I am thinking is that maybe the deterrant coatings, in the combustion process, reform into basic NG (or something remarkably similar...combustion rarely has complete, 'stable' molecules in the middle of the process) before burning. That would/could explain the deterrant effect...the time and energy required to reform, as well as the presence late in the combustion process.

To make a long story short, I remember enough of my college organic chemistry as well as some years in a trace metals lab to wonder how an accurate measurement is made at the temperatures and pressures in a rifle barrel. I was thinking about a gas chromatograph, but keeping the NG from finishing combustion was holding my logic process up. Maybe examing for resudial gases...can be done but is tricky with multiple chemicals involved....??? A very small hole in the barrel would give a LOT of cooling effect as the gases exited, both from expansion effects and heat transfer to barrel metal...

If you ever find out more, my curiosity is well and truely up. I would appreciate any data you find. Thanks!