My (warped) understanding of "detonation" is that it occurs in large capacity cartridges with very light charges of gunpowder. The effect is a very high pressure peak that can damage or even destroy a firearm. Nobody seems to know for sure why this occurs. Any thoughts, ideas, theories, experiences, published articles or books would be much appreciated.

Good shooting.

Robert

M.L. McPherson, a writer for Precision Shooter magazine (writes for Rifle Shooter also) recently wrote an article about how the positioning of the powder in the case (when less than full) can affect pressure and velocity....it was very interesting. My understanding of the problem you describe is that it happens much like an explosion in a grain elevator (an I think it is a simplistic explanation). A case with little powder sits in the chamber and the powder lies on the bottom of the case...the gun is fired and the primer ignites part of the powder and put the rest of the powder into "suspension" which then explodes causing the problem. You can cause a similar explosion using a small amount of common kitchen flour in an empty coffee can strong enough to blow the lid 20 feet into the air.

What happens is that the powder charge may be ignited over too large of a surface area and the pressure will build too fast. That is why most reloaders use a powder that will occupy 85% or more of the case capacity.

I almost forgot, you can make a good comparison with IMR-4831 and Alliant Unique. At a loading ratio of 30% of case capacity, The 4831, IF Ignited Just Right, will burn at a much faster rate than intended, just like substituting Unique for 4831 in say a .30-06. The only thing that will happen will be BAD.
For all intents and purposes, no one would

[This message has been edited by DaveC (edited 05-10-2001).]

DB Bill,
A grain elevator explosion happens when the atmosphere, (either in a room or silo) gets saturated with dust (dirt or flour) to a high enough concentration that if there is a spark, a flash will occur and end up in a flame front moving from particle to particle, always expanding and will build enough pressure in a confind space to create an explosion. In an effort to reduce the chances of explosion, all elevators and grain mills are required to spray mineral oil on the products to reduce dust.
Dirt or flour laying on the ground will not burn, only when stirred up to the right concentration with air will it be capable of carrying a flash.

In a chamber with a properly loaded and headspaced cartridge, a combination of events can turn a safe load into a bomb. Lets say that the bullet is seated about .05 off the lands. The primer ignites with enough power to dislodge the bullet from the case and jam it into the lands. The powder for whatever reason ignites a few miliseconds after it should have (moisture, bad lot, oil) and it does so just after the bullet has come to a complete stop from the primer's initial push. A scenario like that can happen and will likely result in a blowup and pressures probably about double what they should be.

-redleg

[This message has been edited by redleg155 (edited 05-10-2001).]

I have heard that detonation can also occur when a light charge of powder is positioned to the front of the case, near the base of the seated bullet. Something about the pressure wave expanding rearwards, instead of forward.

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Happiness is a 200 yard bughole.

I read a study of this a while back and they seem to think it is because a pressure wave of expanding gas moves forward and hits the base of the bullet, and since the bullet isn't moving very fast, or not at all, the forward part of the pressure wave then moves back towards the primer end of the case and hits the back part of the pressure wave, which is still moving forward. This then causes a tremendous build up of pressure within the case.