Blowup question

[PREMOD70]

I don't wish to start a problem but there is a post on another site that causes me to question the statement and I would like your input without stirring the pot of dissent so here goes the the thread;

Detonation can occur even at low pressure with a very light powder charge and with the same results...leading the shooter and spectators to assume that a double charge caused it. When it happens in revolvers, it often breaches adjacent chambers and sympathetically sets off the rounds in them...and the resulting explosion is spectacular and dangerous.

Smokeless powder is designed to burn progressively from back to front...much like the flame front in a combustion chamber that lights at the spark plug and travels across the piston. Like a combustion chamber, if the fuel is lit all at once...you have detonation...spark knock's ugly step-sister. It can knock the tops out of pistons and crush rod bearings. Detonation in a gun generally unwraps the gun the first time it happens.

When a too-light powder charge is in a case, it tends to lay flat, exposing the primer flash hole. When the spark comes, instead of punching through the powder charge, it moves unimpeded along the length of it...lighting it all at once, so instead of the charge burning progressively from back to front...it literally explodes...or detonates...setting off the destructive shock wave that blows the chamber.

It's a rarity with undercharges. The conditions have to be just right. The same applies to an overcharge. It's just easier to bring on the detonation with large powder charges and pressure jumps because of the property of smokeless powder to burn faster as the pressure goes up. If you happen to hit the sweet spot with a particular powder and charge weight...ka-flippin'-blooey.

 

[TonyR]

The best explaination of this I have read can be found in Volume II of PO Ackley's "Handbook for Shooters and Reloaders", page 43 in my edition. He discusses possible reasons for detonation when a reduced charge of a slow powder is used in an overbore cartridge. I think this is why most reloading manuals list bopth minimum and maximum charges. He believes that the powder ends up up near the shoulder of the case and is too far from the primer for proper ignition but also mentions other theories.

 

[fullersson]

The quote is from the link about sub-sonic load development. I don't know if you are talking about sub-sonic or not but either way it still deals with low pressures and light powder charge. Brian Brown.

http://members.shaw.ca/cronhelm/DevelopSubsonic.html

"The ultimate danger in subsonic loading is a phenomenon known as Secondary Explosive Effect (SEE). SEE can destroy the strongest rifle action and it can happen on the first shot or the tenth. In fact it is more likely to happen after the bore is dirty from the first few shots. SEE is the result of slow or incomplete ignition of small amounts of smokeless powder. The powder smolders and releases explosive gases which, when finally ignited, detonate in a high order explosion. The warning sign for imminent SEE is a hangfire or delayed ignition.

There are a number of techniques that can be used to prevent or delay the onset of SEE. These involve specially prepared cases as well as bullets, in addition to selecting a suitable powder and primer."

 

[PREMOD70]

Great read so far but when the statement related the incident as revolver related I did a query and found this link;

http://forums.handloads.com/archive/forum_posts.asp?TID=22648&PN=1&TPN=1

and after reading that became concerned but I now wonder if the cause for detonation is not the same as stated on the previous post's link concerning SEE.