Will powder detonate in very light-loaded case?


October 12, 2008, 06:12 PM
There's some mention over in the General discussion board about whether small center fire cartridges can be loaded down to achieve the report of RF ammo. One poster brought up the potential dangers of having so little powder in a case that it detonates, rather than burns. I posted the following there:

"I've read of the dangers of under loading cases too, but can't puzzle out the physics. How would a 1/2 grain or full grain of powder be the tipping point between a fast burn and a detonation? I think I'll scoot over to the reloaders and see what they know about it."

How about it? Is this a real phenomenon or a reloading urban legend?

If you enjoyed reading about "Will powder detonate in very light-loaded case?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
October 12, 2008, 06:37 PM
Smokeless powder simply cannot detonate in the small quantities used in small arms ammunition. There is not enough mass for a detonation shockwave to progress through the charge.

Reports of reduced load blow-up's are generally in large magnum cases that are very over-bore. (Small caliber belted magnums)
It is thought by many, myself included, to be more closely associated with a bore obstruction.

1.The reduced load of slow burning powder is laying on the bottom of the case.
2.The primer flashes over it and doesn't get a complete high-pressure burn going.
3.The bullet moves from the case, and sticks in the first inch or so of rifling.
4.Then the rest of the charge lights off and pressure rises so fast the stuck bullet can't get out of the way fast enough.

IMO: "Detonation" blow-ups in handgun light loads are nothing more then double charges, or more, from faulty reloading procedures. It seems to be a phenonum that happens to pip-squeek load Cowboy action shooters more so then any others.

(Years ago, I saw it in light-load Bullseye shooting where star progressive reloaders were involved.)

Powder only has so much energy in it, and as I already said, cannot support a detonation in less then rail-car quantities.

Carry it a step further.
If smokeless powder can detonate in small quantities, you could stick a fused blasting cap in a pound can of 4831 powder & have a very powerful bomb.

But you can't, because it won't detonate in container size quantities.
Including 8 pound kegs.


October 12, 2008, 06:37 PM
Seems some rifles have blown up when loaded with light charges of slow powders, most often under heavy for caliber bullets. The evidence is there and most ballistics authorities believe it but, so far as I know, no one has ever been able to do it in a lab.

The best guess I've seen is that the bullet gets pushed into the bore so slowly it gets stuck and stops, or nearly so, maybe an inch out. The powder continues to burn and the pressure rapidly spikes, it goes up so fast the bullet cannot "get out of the way" fast enough so pressure continues to spiral up rapidly until the gun blows. Not quite a "detonation" but the effect is much the same.

PS - it appears that RC and I were typing at the same time!

October 12, 2008, 06:51 PM
The evidence is there and most ballistics authorities believe it but, so far as I know, no one has ever been able to do it in a lab.

No one has been able to prove that it happens small arms. It is known that field artillery barrels sometimes burst when the gun is fired with a low charge: This has been duplicated.

October 12, 2008, 06:58 PM
Firearm technology has been aware of the pressure excursion phenomenon. It is commonly called 'Secondary Explosive Effect' among internet forums. I sincerely doubt any of us hobbyists deeply understand the issue, but you may wish to research it more fully. See the entry under SEE in this glossary:

This guy talks about subsonic ammo, and mentions the danger of secondary explosive effect when loading light charges:

I don't pretend to have the credential to tell you all about it.

October 12, 2008, 07:48 PM
I believe it can happen.

Smokeless propellants, of which smokeless powder is a sub set, have very complex combustion reactions. Humans like to think of events in a linear fashion, but most phenomena is exponential. Smokeless pressure curves are exponential. Funny things can happen with exponential systems.

The modeling of smokeless propellants has been conducted for years. The rocket industry has had numerous occasions where fully loaded rocket motors blow up. The class I attended, the explanation they used was that pressure waves collided.

I read an article describing the detonation of flammable gases. The proposed computer simulation and discussion would be in line with detonations with small powder charges. The article came out of the 8 March 2003 New Scientist magazine.

Basically a few molecules could leap ahead of the main shock wave, triggering further reactions so the explosion turns into a detonation.

I would say 99.9% of detonations in cartridges are due to bad reloads, but this phenomena has happened enough that it is common knowledge not to use reduced charges in large cases.

October 12, 2008, 07:55 PM
seem to happen "they" say from certain powders.bullseye is blamed by some BUT it is double charges with that powder.If your case is sized to handle small charges it wont. meaning 25acp for little charge.:uhoh::rolleyes:

October 12, 2008, 07:58 PM
rcmodel nailed it....but the 243 Winchester is also known for light charges blowing up guns.

Jim Watson
October 12, 2008, 08:24 PM
Ackley reported high pressure from reduced loads of slow burning rifle powder.
Some nitwit chambered a Rolling Block for .250 magnum, as I recall; then tried to make a .257 Roberts out of it just by loading less extra slow powder.

Never saw report of a reliable case of a light load of pistol powder "detonating."

One rather famous case of a SAA blowing up with light CAS loads was checked out. The owner said there was no way he could have double charged the powder in that .45 Colt, it must have "detonated." A couple of experienced reloaders watched him at work, and sure enough, his methods precluded double powder charges. But after a while, he managed to seat two bullets in one case. Bullet lube deposits stuck one in the seating die, he assumed he had neglected to position one and put another in place. The next handle stroke seated both. Naturally the observers stopped him and pointed out the problem. 500 grains of lead over even a pistol load had not been good for the gun the first time and they did not want him trying it again.

October 12, 2008, 09:07 PM
So . . . what's the answer then? So far they fall into these categories:
It depends.

Well, let's say it is a risk. Would the .22-250 fall into small diameter/large capacity list of troublemakers? Would one see any signs of potential detonation before a squib load, or a straight-out detonation?

October 12, 2008, 09:26 PM
Tell me "EXACTLY" which round (223, 308, etc.) you are wondering about and I'll give you a more definitive answer.

Slow burning pistol powders can be used in some rounds. but not all.

And light charges (of less than listed minimums) of slow burning rifle powders are usually a very bad idea.

October 12, 2008, 09:37 PM
Deleted by OP.

October 12, 2008, 10:06 PM
"Are .22 CB longs safe indoors?"

I believe you are quite safe from a detonation from a light charge of slow powder.

October 12, 2008, 10:57 PM
Firearms Pressure Factors, by Lloyd E. Brownell, Ph.D., Wolfe Press 1990 is an excellent work on the subject of the title of the book.

The first three chapters give a basic overview of the problem of 'pressure excursions', the scientific, descriptive term for the action that blows up firearms. I'm not going to download the first three chapters of the book for everyone. It would be tedious and probably a copyright infringement. It's a paperback, it isn't all that expensive and it's worth reading and having in one's library.

Guys, it's real, it happens. And no one - yet - knows exactly what causes it. However, the combination of large capacity cases and small amounts of slow burning powder is the basic scenario. Unfortunately, it still remains to be done on demand. I say 'unfortunately' as some refuse to believe it under those circumstances and fool around with reduced loads of slow powder. Those folks usually add to the information regarding the occurrence at some point. (Hopefully they keep records of their loads.)

This slow powder/small charge is most pronounced in rifles. The same occurrence in handgun cartridges seems to be more explained by double charges - or double bullets. (I for the life of me can't see seating two bullets in a handgun case and not noticing. There's a first time for everything, I suppose.) (And that's not to say I haven't done some rather silly things in my reloading career.)

October 13, 2008, 02:23 AM
I've heard of people putting a little tissue paper in the case, over the powder and under the bullet, so the powder lights more evenly when you have a large case and not that much volume of powder.


October 13, 2008, 02:26 AM
Thanks, Archie. Mystery solved. Now if I can only figure out how light a load I could run through my .22-250 without becoming a statistic.

And Ranger 335v, thanks for your re-assurances on the CBs. I was pretty worried about that.;)

October 13, 2008, 10:00 AM
http://i338.photobucket.com/albums/n420/joe1944usa/collapsedshoulder.jpg This is one thing that can happen using slow burning powder/light charge. The brass does not seal the bore, the hot gas comes back and smashes the case. For a detonate to happen something has to be plugged so the powder can build pressure like in bomb making. Or the round has to be crimped into the chamber by the trim length being to long, or the loaded round neck diameter is to large for the chamber, crimping the round into the chamber. OR In addition, certain smokeless powders with a high-nitroglycerine concentration can be induced to detonate Scroll down to "Improvised Explosive Devices"

http://www.fbi.gov/hq/lab/fsc/backissu/april2002/mccord.htm When smokeless powders are in the open air, they just burn slowly, unlike black powder that flashes.

October 13, 2008, 10:35 AM
But you can't, because it won't detonate in container size quantities.
Including 8 pound kegs.

Want to bet? Even a VERY small quantity of smokeless powder can be detonated with a primary high explosive... DBSP is simply flaked secondary HE. :)

October 13, 2008, 02:35 PM
There is really no reason to light load with slow powder in the first place.

Suggest you read this:

The 60% rule using H4895 should work quite well in the 22-250.

If still in doubt, call Hodgdon and ask them about it.

As for the lightest 22-250 load I have used?

Just a MLR primer and a .22 air-rifle pellet knocks the stuffing out of barn pigeons!


October 13, 2008, 06:51 PM
Just a MLR primer and a .22 air-rifle pellet knocks the stuffing out of barn pigeons!Hmmm........ :evil:

October 13, 2008, 10:41 PM
rcmodeler, that is an intriguing possibility. Any pellet preference? Brand, weight, shape?

October 14, 2008, 01:13 PM
Flat-point pellets kill far better then pointed or round nose.

Other then that, doesn't matter what brand.


October 14, 2008, 06:54 PM
For such light loads could you not use a case filler on top of the powder and under the bullet?

Wouldn't this hold the powder directly against the flash holes for the primer and solve the problem?

October 15, 2008, 01:23 PM
Well then you got a big wad of case filler that has to be pushed past the bottleneck and into the barrel.

People do it using Kapoc, and Cream of Wheat, and Puff-Lon and other stuff.

But if you just use the proper kind of powder for reduced loads to start with, it really isn't needed in most cases.


October 15, 2008, 01:34 PM
If you simply use a powder reccomended for light loads, you will likely forego the after effects ofa blowup. SR 4759 and Trail boss are known fluffy powders meant for reduced pistol and rifle loads.

I use 8 gr of Trail boss behind a 150 or 165 gr lead or plated bullet, in the 30-30. Likely you can use either of those for reduced loads.

If you enjoyed reading about "Will powder detonate in very light-loaded case?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!