IMR Trail Boss ?

[Unclenick]

Hafoc,

You are correct that detonation is not well understood. Quite a number of theories out there. The problem is lack of repeatability. O'Conner noted it with surplus 4831 many years ago. For a long time the assumption was it only came up with slow rifle powders when someone was trying to fire squib loads (a few grains) and left a lot of open space. Then one of the Finnish web sites has some extensive detail that, if I recall correctly, included documentation going back to faster rifle powders.

At any rate, it seems to be OK to shoot fast pistol powders without worrying about lower limits. Most common rifle powders, like IMR-4895 recommend you don't let it get much below 2/3 filled case capacity.

The effect that is proving repeatable is secondary pressure spiking from firing light bullets with slow powder. This is a phenomenon in which an accumulation of unburned propellant detonates right near the base of the bullet when it is over 18" or more down the tube. Texas gunsmith Charlie Sisk has blown the muzzles off several guns in demonstrations of this.

Nick