Light Load DETONATIONS...?

[BusMaster007]

Someone said to ask HERE, so here's the link to the thread where the discussion is:

http://www.thehighroad.org/showthread.php?p=1516917#post1516917

Basically, we're wondering if a light load can blow up.

Maybe someone who frequents the Reloading Section remembers the magazine articles I refer to and can comment on that.

Thanks.

 

[Black Snowman]

The subject has come up and as I recall no one could find any proof that an extremely light load alone has created a detonation. Normally the danger of very light loads are inconsistant iginition resulting in a stuck bullet from a "squib" that creates an obstruction for the next round.

 

[pbhome71]

Here something to think about... Second peak pressure from light load. I got this from RSI. They, actually he, designed, and manufactures pressure guage for handloader. If you call Jim up, he will keep on talking. He is a very nice guy.

Here is an example of a scary light bullet load recommended in several load manuals taken from a .223 bolt action rifle. Note the secondary pressure spike just as the bullet exits the muzzle and how the pressure traces do not overlay nicely with each successive shot.

This is characteristic of "finicky" bad loads and is probably caused by a pressure shock wave and/or secondary ignition because the powder burn rate is too slow. The exact cause of the secondary pressure spike may never be determined but it is real. Altering the bullet seating depth, powder charge and even adding a 35 lb. sand bag to the barrel did not eliminate or significantly alter the spike.

If I remember correctly. As the powder burnt, the initial pressure drove the bullet forward. As the power burnt more the expanding gas caught up with the travelling bullet and causes secondary spike. However, as he said, "the real reason may never be determined..."

I have just ordered the Pressuretrace and have not have time to play with it, yet.

 

[pbhome71]

Here's more discussion... It may be product specific, so please take it with a grain of salt.

From - http://www.shootingsoftware.com/barrel.htm

Secondary Pressures

PressureTrace collects more data then competitive products previously used by shooters. Our output is also not filtered or "smoothed" so "what you see is what occurred". Other strain gage systems either do not collect sufficient data to see anomalous secondary pressures or they are filtering it out as noise.

A short-lived debate occurred when shooters could first see the severity of some secondary pressure spikes. Understandably, some shooters did not want to accept how often it occurs or the severity; especially when the subject has been largely ignored by shooting magazines.

A conclusion by some was that PressureTrace picked up barrel harmonics. In an attempt to prove this theory one shooter even hung a bowling ball off the end of his barrel, but of course there was no change.

Strain gages change resistance when stretched in one direction. A strain gage glued "around" the chamber can only detect radial expansion of the steel under the gage. Only if a gage were attached longitudinally on a barrel would it be able to detect barrel "whip". Even then, movement at the thickest part of the barrel shows only minor current changes that appear as slight "squiggles" in a trace. Public debate over whether these secondary spikes are real was finally put to bed when Charley Sisk at Sisk Rifles blew the end off two barrels. Case Closed, it is real!

Indeed powder formulators and powder manufacturers have known about this phenomenon for some time. I first heard about it more then 20 years ago, before good instrumentation was readily available, and in reference to ball powders. A friend who worked at one of the powder companies once told me, "If consistency of performance where the only issue in powder design, ball powders would not exist. Ball powders are simply less expensive to manufacture and make it easier to produce ammo with consistent charges." He then went on to explain, " The three primary formulation features of powder is nitrocellulose content (or base material composition), granule shape and granule coatings. If the granule shape is spherical, then coatings become far more important to maintain a desired burn rate. Unfortunately coatings can burn off and are not the most reliable way to maintain a burn rate for every circumstance."

Power companies have no control over how a particular powder will be used. They must rely on ammo manufacturers and those who produce load manuals to keep things safe. Ammo manufacturers and compilers of load manuals do a tremendous job, but there is no way they can anticipate every possible combination that will cause secondary pressures. Given the litigious nature of our society, this is a real touchy subject, and most in the industry would prefer shooters remain ignorant of the phenomenon.

 

[only1asterisk]

pbhome71,

That was a light load of "slow" (for application) powder. This is a pretty good way of wrecking a gun. It should be pretty well proven to most people by now. I don't see any room for debate.

The contention that light loads of fast burning powders produce the same effect is absolutely unproven. You would think that if the effect is reproducible with slow powders, it should be reproducible with fast powders too. While the double curve may be found, the pressures are never enough to get you in trouble.
The idea that all light loads are bad is TOTAL BS. Using the right powder, greatly reduced loads are perfectly safe.


David

 

[Fumbler]

The problem isn't double chrages of fast powder, it is very light loads of relatively slow powders (like H110 in .357mag).

The problem isn't the light loads causing kB!'s, the problem is the slow powders won't ignite because the flash can't reach the powder and the primer pushes the bullet into the barrel causing a bore obstruction for the next shot.

 

[Black Snowman]

Thanks for that post pbhome71. It's always good to have some solid info.

 

[grendelbane]

The problem isn't the light loads causing kB!'s, the problem is the slow powders won't ignite because the flash can't reach the powder and the primer pushes the bullet into the barrel causing a bore obstruction for the next shot.

I have done half of that.

Yes, it can happen. I was fortunate, I did not fire that second shot. It was too light of a load of 296, (H-110's twin brother), in a .45 Colt.

The bullet made it half-way down the barrel. The load was from a reputable bullet manufacturer's loading manual.

296 is a good powder, but believe Winchester when they say not to use reduced loads.

 

[mete]

Thanks , that graph is a very clear illustration of what can happen with bad loading practices. Unfortunately there are many who refuse to believe it !!

 

[griz]

I'll preface this by saying I am not trying to call anybody a liar, just asking a question.

If the second pressure rise is real, and assuming that it is coming just before the bullet leaves the barrel, why are barrels built tapered toward the muzzle? Or more to the point, why don't they all blow up at the muzzle?

It seems to me that there is a long history of our technology accepting that the high pressure occurs in the first part of bullet travel, and as such we need more evidence than one chart to qualify as proof of this second spike.

 

[Fumbler]

If the second pressure rise is real, and assuming that it is coming just before the bullet leaves the barrel, why are barrels built tapered toward the muzzle? Or more to the point, why don't they all blow up at the muzzle?

They are tapered because the loads in question are unusually light loads. Commercial ammo will never be loaded like that.

I remember reading a test where a man turned a 30-06 barrel down, 1 inch in front of the chamber, to increasingly smaller diameters. He would fire ammo between each diameter reduction and the barrel did not rupture until the barrel wall was only 1/16 of an inch thick.

 

[Third_Rail]

Detonation of DBSP (modern double base smokeless powder) is harder to achieve than through a primer.

You need a primary high explosive with a booster charge to get it to detonate. I thought we all went over this before.

 

[mete]

Griz, go to the website and take a look at the normal graphs [without spike ] and compare with the spiked one. These problems have been noted by a number of knowledgeble shooters for at least 30 years but it has taken a while to prove it as the graph does.

 

[BluesBear]

I'll bet a dollar to a doughnut that the light load featured in the graph exhibited quite a bright muzzle flash.

Muzzle flash is caused by the escape of burning gases. In theory a light charge should burn completely before the bullet leaves the muzzle and flash should be decreased.

What is happening to the rounds in the graph is a classic case of inconsistent powder burn.

In very light loads, where there is no filler used, the powder is spread out over the "floor" of the case. The primer ignites only a part of the powder and the resulting pressure forces the bullet and a portion of the powder charge down the barrel. One the pressure drops low enough the heat ignites the remaining powder. Usually the secondary pressure spike is still within SAAMI parameters.



When testing very light loads place a large piece of white butcher paper on the ground about 3 feet to 6 feet in front of your muzzle and in many cases you will be surprised at the amount of unburned powder you'll recover.

 

[griz]

OK, I looked at their site but I'm still not sold. I will not dispute the claims of detonations with reduced loads of slow powders. But these folks are talking about secondary high pressure spikes from common recommended loads of recommended powders. That is something else.

In the example shown here they blame it on the type of powder. I've never tried 2230, but many people have used it in 223's with much success. For what they say to be true, Accurate Arms would have had to know they are selling a dangerous powder, and still recommended it for that application.

They give another example where the pressure was almost 120,000 PSI at the muzzle with "reference" ammunition. They do not say if that is a handload or factory. Here I will repeat my question: why doesn't the gun blow up if the pressure is that high just before the bullet leaves? That would be twice the guns rated pressure, applied at the thinnest part of the barrel, the part not designed to even take the SAMMI max, so the barrel should let go.

They even say that factory loaded ammunition can have these dangerous pressures but apparently most of the ballistics labs in the country either have unsophisticated equipment that will not pick up the spike or are covering up the problem to keep sales high.

And last is this from their site:

Note: Secondary pressures readings taken at the chamber are lower and of longer duration then the actual event due to compression of gasses behind the bullet and the time required for expansion and contraction of barrel steel. The above event may have spanned only .1 milliseconds of time but could have reached 150,000 PSI!

This doesn't add up to me. I'm familiar with strain gages and their use, although I've never used one on a firearm. But they can install the strain gage on any part of the barrel they desire. There is no reason to limit their use to the chamber area. So to make that claim is unsupported speculation that could be verified if they choose to.

What do I think is going on? I think they are measuring some false pressure that only shows up in some loads. I don't know why it shows up at all, much less why with certain combinations only. But I do know that guns are not indestructible, and if you apply pressures as indicated by their instrumentation it would blow up the end of the barrel. (Yes I saw their claim that Sisk had this happen, but their link does not confirm it) At the end of their page they say there will still be doubters. Put me down in that category.

 

[cracked butt]

ntxt

 

[cracked butt]

I think if there was much truth to the article, cast bullet rifle shooters would be blowing themselves up in droves.

Lead bullets take very little pressure to push them down the bore, and shooters use powders ranging from light loads of fast burning powders like unique red dot, to loads of IMR-4227 and 2400 with a lot of space in the cases, to light loads of slower burning rifle powders like 4831 to 4895.

Powder burn rate too slow for the bullet.
Bullet weight too light for the powder's burn rate.
Bullet bore contact area less then normal for the bullet weight
Barrel longer then normal
Bore severely worn or incorrectly lapped (loose/worn toward the muzzle)
Moly in bore or moly coated bullets that reduce bore friction

 

[Master Blaster]

First off the Chart above it proports to show the dangerous effect of a light load. NONSENSE it shows no such thing.

From the Accurate arms data on their website:

http://www.accuratepowder.com/data/PerCaliber2Guide/Rifle/Standarddata(Rifle)/22Cal(5.56mm)/223%20Remington%20pages%20185%20to%20187.pdf

AA2230 40 grain Nosler BT max charge 26.4 FPS 3666 Pressure in CUP 51,562.

The chart above is showing a load that is .5 grains above the maximum load in the AA data. The AA data shows pressure in CUP so add 10% to convert to PSI ( a rough estimate not reliable) you get 57,000 PSI and the folks doing the test have added half a grain to the max load so 61-65,000 PSI is not out of reason for the load they are showing.

The load they are showing is not a light load.

So their theory about detonation based upon this evidence is

 

[g56]

Looking at their charts and reading the article, my first thought is the phenomena he is showing might be related to his software or measuring equipment and may not even exist in real life.

I could be wrong, but what he is saying defies logic.

 

[Vern Humphrey]

For years there have been cases of guns blowing up with reduced charges. For a long time there was supposed to be a "detonation" phenominon -- and this was associated with reduced charges of slow-burning powders.

Again and again, examination revealed there was no "detonation." A detonation is a chemical reaction propagated by a shock wave -- and it's characteristic signature in steel is shattering, with a chrystaline structure plainly visible at the breaking point. All guns that blew up showed the stretching consistent with high pressuers, not with shockwaves.

The double spike phenominon shown in the graphs has been seen in many cases, and the explanation -- that the primer drives the bullet into the rifling, where it sticks, and a fraction of a second later the powder ignites, is the one most accepted by most ballisticians.

Note that some reloading manuals now caution against reducing recommended loads in some powders.

 

[Art Eatman]

About 30 or 35 years ago, a doctor brought a .243 rifle to the attention of the NRA staff. It was wrecked. The story, as I recall it, was that the doctor was adamant that he had not double-charged with a light load.

IIRC, the charge was around 25 grains, and of 3031. Now, a max load of 40 grains of 3031 (behind a 70-grain bullet) almost fills the case; I can believe that he didn't successfully load 50 grains into it.

At the time, the consensus was, "We don't know why."

Now, 35 years ago, nobody ever spoke of a "double spike"; that phenomenon wasn't known.

Stipulating the doctor was correct, this is the only recorded case of which I know about a light load and detonation. Ever since then, powder manufacturers have spoken against using slow-burning powders in reduced charging. (May have been other events; I haven't read of them, is all. Shrug.)

I've long used pistol and shotgun powders in reduced loads in my '06--since 1950. More recently I did the same for .30-30, .30-40 and .308. No problems whatsoever. I've found that 2400 works, and that's plenty good for me.

FWIW, Art

 

[Vern Humphrey]

Quote:
-------------------------
Stipulating the doctor was correct, this is the only recorded case of which I know about a light load and detonation.
--------------------------

Not a "detonation." The rifle exhibited the characteristic stretching of excess pressure, not the shattering associated with detonation.

The best bet is a hangfire in which the primer drives the bullet into the rifling before the powder ignites.

 

[Clark]

When I plug the bullet, powder, caliber, and charge into Quickload, it gives me about the same pressure for the first hump, and just as the second hump starts, the bullet exits the barrel at .9 milli seconds.

I am designing a strain gauge amplifier, and I have a circuit to cut out the second hump. That is when the gun makes a big bang sound and the barrel rings like a bell. It has little to do with the peak pressure of the load.

I don't worry about detonation, no one has ever been able to replicate
it, and many have tried.
I don't believe in crop circles, UFOs, global warming, second hand
smoke, the Bermuda Triangle, Bigfoot, or leprechauns either.

 

[griz]

the bullet exits the barrel at .9 milli seconds.

My first impression was their data was showing a problem with the equipment reacting to the near instantaneous drop in pressure when the bullet left the barrel. Glad to hear some confirmation of barrel time, I didn't know how long it was.

 

[Gewehr98]

Anybody remember the old phrase...

"2.8gr Bullseye Surprise"? (With respect to .38 Special light wadcutter loads)