Pressure Spikes Caused by Underloaded Cartridges

[Old Sandman 71]

I ran across a reference in Kuhnhausen's shop manual for the SAA that under-loaded cartridges, (loaded to less than the minimum charge listed in a loading manual) can produce "random spikes in pressure" (pg 27; figure 17) that can result in catastrophic damage to a gun.

I can understand charges that are too low can lodge a bullet in the barrel, but I've never seen any reference to this phenomenon in any loading manual that I've read. My guess is that these pressure spikes are related to cartridges that were originally designed to hold a large volume of black powder (.45 Colt, .38-40, 44-40 for example) being filled with a relativity smaller volume of smokeless causing problems due to the distance the powder is from the primer in a largely empty case. Am I in the ballpark?

Since I still consider myself a neophyte in the world of reloading, I wonder if some of you who have more experience could explain the and physics behind these spikes?

Thanks

 

[ATLDave]

This refers to the controversial claim of "detonation." Some awfully smart people have tried to recreate it without success. But some other smart people are very insistent that it is a real thing and a real danger.

 

[MEHavey]

Using the [normally] fast powders in SAAMI-loaded SAAs, no problem.
There are, however many "detonation" warnings about underloading high-enegy/slow/ball powders like W296/H110.
(But even then... lot'sa very competent folks have begun to question the whole ball powder/detonation lore.)

That said, UnderMin/Slow ball does engender dramatic velocity variations as burn is erratic, and I've personally seen multiple
instances where the ball powder just fuses together -- unburned -- and results in a squib.

 

[tcoz]

And that's why Hodgdon says never to go more than 3% below minimum with H110

 

[Old Sandman 71]

ATLDave-

So what's your take on what actually happens to cause "detonation" in an underloaded cartridge, verses normal explosion, ignition (not sure of proper term to use here) in a correctly loaded cartridge?

 

[mdi]

Could be wrong (and I don't have an opinion on "detonation"), but I read that a large air space, and the shock wave traveling up to the base of the bullet can cause extreme pressure; detonation. But, I've never read of anyone being able to replicate a detonation on purpose...

 

[Jlr2267]

And that's why Hodgdon says never to go more than 3% below minimum with H110

no, that's not why...it is to avoid possible poor ignition and a projectile stuck in the bore

 

[fguffey]

Could be wrong (and I don't have an opinion on "detonation"), but I read that a large air space, and the shock wave traveling up to the base of the bullet can cause extreme pressure; detonation. But, I've never read of anyone being able to replicate a detonation on purpose

I have primers that are strong enough to seat the bullet into the rifling.
Seating bullets into the rifling is a gad habit. When I do not fill the case with powder the flash of the primer seats the bullet before the powder starts burning 'OR' the primer ignites the powder lying in the case. That does not seem like a problem but the area ignited causes the powder to burn from the top down instead of from the back to the front.

Not forgetting about the stuck bullet, once the burning powder builds pressure the bullet does not have time to get out of the way.

I am the fan of the jump start, I want my bullets to have the running start. I do not seat my bullets into the land.

F. Guffey

 

[fguffey]

http://thefiringline.com/forums/showthread.php?t=341348

F. Guffey

 

[ATLDave]

So what's your take on what actually happens to cause "detonation" in an underloaded cartridge, verses normal explosion, ignition (not sure of proper term to use here) in a correctly loaded cartridge?

My take is that I don't know whether that occurs at all. Claimed instances of detonation might be the result of either an obstructed bore (prior shot stuck) or a double charge. Double charges are certainly easier with a small charge of powder that cannot easily be seen in the bottom of a large case.

Or maybe they do happen. I don't know. But I'm not convinced that they definitely do occur.

 

[Lost Sheep]

Opinions vary

Some people believe the phenomena known as "Secondary Explosive Effect" (S.E.E.) or "Detonation" or "Flashover" or "Ringing" (of barrels due to resonation of pressure waves in a barrel or by a bullet halting partway down a barrel before the powder charge really gets to burning) happens and some deny these are possible. Internal Ballistics is not an exact science and reproducing these effects is difficult, even in the best ballistics labs.

I used to think the danger was limited to light charges of slow powders until I read first-hand testimony of a fellow who was fire-forming brass with light charges of a moderatly fast powder (a generally accepted practice). He blew up his Thompson-Contender (a very strong gun), evidently because he let the powder charge fall to the front of the case instead of keeping it near the primer.

Here is a web page that contains several articles for you to consider, including the story I mentioned above (it is the article titled, "A RELOADING DEBACLE" by Charles J. Sharps Ph.D.):

http://reloadammo.com/liteload.htm

Lost Sheep

 

[dh1633pm]

I load 45-70 a lot. I load it hot and I load it not. When I load it "not hot" or mild loads, I use Unique at about 11 grains. (WARNING LITTLE BIT OF POWDER IN BIG CARTRIDGE USE AT YOUR OWN RISK).

You can find loads using Unique and the 45-70 all over the Internet, but still its a little bit it a big amount of space. Since I don't shoot straight up, I do use something to hold the powder down. Two squares. Yes two squares of good ol toilet paper, jammed down hard inside the shell. Works like a charm. Side benefit is the explosion of the toilet paper, especially near night fall.

I don't know if light loads in big cartridges is dangerous or not, so why take chances. With this load and a slight elevated rifle, I can lob a 300 grainer and hit a 200 yard target, but now I am getting off topic.

Would be good to know who worried about the problem and how they work their loads in an attempt to manage the problem, that may or may not exist. But better safe than sorry. Cream of wheat anyone? Polyfill?

 

[Old Sandman 71]

Your responses have given me enough info to begin to understand what's going on, especially helpful was the link to the "reloading debacle".
It crossed my mind when I loaded my first 38-40 cartridge with 4.6 grains of Accurate #2 and peered down into a mostly empty case that it might be wise to add a filler on top!
Thanks

 

[refuse2bafool]

Further Info

Mike Venturino wrote this article about it 20 years ago. He thinks its due to very light charges of fast burning pistol powder and large capacity cases such as magnum and old black powder cases.

Richard Lee talked about it happening with reduced charges of slow burning powders and large capacity rifle cases.

My own take is that it is hard for me to believe these are all due to double charges, so I do not go significantly below the reloading tables in any large capacity case. If the table only list a maximum charge I will reduce no more than about 10%

 

[MEHavey]

Guys... I'm having a real hard time accepting the anecdotal evidence
(which I admit does exist) beyond the point inexplicable/non-repeatable
lightning strike. ...and when something is "inexplicable/non-repeatable,"
grizzled old scientists tend to put it into the category of the supernatural.

(I was particularly struck by the 2nd-to-last paragraph in the Veneturino
article concerning total energy availble from a light charge)


Has ANYONE done any disciplined 3D hydrocode/strength-of-materials
workup/testing in this arena?

 

[243winxb]

No catastrophic damage seen- Just pressure spikes

Pressure Spikes have been seen when primers moved the bullet to soon in 9mm. Higher extreme variations in pressure and velocity in the lower pressure regimes of the start loads have been seen in rifles. See link. http://www.shootingtimes.com/ammo/ammunition_st_mamotaip_200909/ Here is a rifle problem. http://thefiringline.com/forums/showthread.php?p=4928827

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[MEHavey]

http://www.shootingtimes.com/ammo/ammunition_st_mamotaip_200909/

Great primer article.

 

[BSA1]

This is a well known and debated topic in Cowboy Action Shooting. SASS rules encourage use of low power ammunition. This is especially dangerous in large volume cartridges such as 45 Colt. I have personally seen three revolvers blow up on SASS matches. Two were clearly overcharged loads. One the cause was never determined.

 

[ljnowell]

It doesn't happen. If it did it could be recreated. And they have tried.

When people blame detonation it's a double charge it a squib followed by another round.

 

[refuse2bafool]

There are always things we don't understand

MEHavey,

I am not a scientist, but between applications of Just for Men I am a semi grizzled engineer. I don’t disagree with you. These phenomena do seem to violate the First Law of Thermodynamics.

A scientist’s ultimate goal is as complete an understanding of natural law as possible. An engineer has to get a job done. "Just enough" knowledge is his minimum criteria.

I am confident that listed loads have been sufficiently tested in both the lab and in real use to be considered “safe”. I like to shoot light loads, but I do not see any reason for super light loads, so I will not take the chance. For me the Zeroeth Law of Reloading is to err on the safe side.

Maybe the fact this only occurs with large capacity cases and light loads is indicative of double charges (my biggest concern). I just don’t know.

 

[243winxb]

If the bullet can exit the cartridge, i dont see a problem.

When the explosive charge is confined in a closed container.

The safest and most powerful low-order explosive is smokeless powder. These powders decompose at rates up to 1,000 meters per second and produce a propelling action that makes them suitable for use in ammunition. However, the slower burning rate of smokeless powder should not be underestimated. The explosive power of smokeless powder is extremely dangerous when confined to a small container. In addition, certain smokeless powders with a high-nitroglycerine concentration can be induced to detonate. On the other hand, high-order explosives do not need containment to demonstrate their explosive effects (Saferstein 1998). These materials detonate at rates from 1,000 to 8,500 meters per second, producing a shock wave with an outward rush of gases at supersonic speeds. This effect proves to be more destructive than the fragmented debris.

http://www.firearmsid.com/Feature%20Articles/McCord_gunpowder/

 

[bluetopper]

This scenario doesn't even move the needle on my meter of things to worry about.

 

[tcoz]

I'm a scientist and as such I look for evidence that can be studied for any phenomenon. In this case we have a number of anecdotal reports, many from excellent sources, and many reasonably possible explanations but what we don't have is the ability to recreate the phenomenon and thereby study it, and for that reason I'm skeptical but not totally disbelieving.

 

[mongoose33]

When the explosive charge is confined in a closed container. http://www.firearmsid.com/Feature%20Articles/McCord_gunpowder/

The safest and most powerful low-order explosive is smokeless powder. These powders decompose at rates up to 1,000 meters per second and produce a propelling action that makes them suitable for use in ammunition. However, the slower burning rate of smokeless powder should not be underestimated. The explosive power of smokeless powder is extremely dangerous when confined to a small container. In addition, certain smokeless powders with a high-nitroglycerine concentration can be induced to detonate. On the other hand, high-order explosives do not need containment to demonstrate their explosive effects (Saferstein 1998). These materials detonate at rates from 1,000 to 8,500 meters per second, producing a shock wave with an outward rush of gases at supersonic speeds. This effect proves to be more destructive than the fragmented debris.

Thank you--makes me wonder if anyone has checked to see if the type of powder in these "detonation events" is the high nitroglycerin powders, i.e., double-base versus single base.

 

[mongoose33]

I'm a scientist and as such I look for evidence that can be studied for any phenomenon. In this case we have a number of anecdotal reports, many from excellent sources, and many reasonably possible explanations but what we don't have is the ability to recreate the phenomenon and thereby study it, and for that reason I'm skeptical but not totally disbelieving.

I am as well and these kinds of situations are all about demonstrating causality. To do that you need to show correlation between cause and effect, the proper time order (cause must precede effect), and nonspuriousness, i.e., there is no alternative explanation that can account for the relationship between cause and effect.

In this case, we have two problems in demonstrating causality: we can't consistently show correlation, and as a result we can't show that we have eliminated all possible alternative explanations.

243WinXB's quote above is interesting; I haven't collected nor collated these anecdotal events, but I wonder if, for example, these anecdotal events only occur with the handloader using double-base powders. On the other hand, if some of these detonation events are occurring with single-base powders, that suggests the double-base powder explanation isn't correct, or at least is incomplete.

Interesting problem.