From: sfaber@ihlpb.att.com (Steven R Faber)
Subject: Re: Powder Detonation [LONG]
Organization: AT&T

From article <92Nov13.001503edt.6357@skule.ecf.toronto.edu>, by reidld@ecf.toronto.edu (Lloyd D Reid):

# Occasionally the topic of powder 'detonation' comes up in this
# group.  I find the subject rather interesting, and would like to
# offer a theory as to what is happening.
#
# First, I'll describe some of the reported causes of the problem that
# I am aware of:
# - a lower than normal powder charge sometimes results in abnormally high
# pressure increases.  Blown primers, stuck cases, or worse....
# - loose powder charges seem to make the problem worse (that is, an increase
# in the ammount of 'ullage' - (thats fancy talk for 'empty space'))
# - cold weather can sometimes make the problem worse
# - happens in the larger rifle cartridges (at least, I haven't heard about
# it in shotgun or pistol cartridges)
# - ball powders are more susceptible
# - slower burning powders are more susceptible
# - magnum primers are recommended as a way to reduce the problem
#
# If you are unfamiliar with the interior ballistic cycle, I have attempted
# to give an explanation at the end of this posting.
#

Nice "survey" article.  You make a good case for irratic ignition
being a factor due to cold temp, or weaker primers.

There was a recent "Guns n Ammo" article on "detonation"
in handguns.  They had some examples where lightly loaded rounds with
Bullseye would blow up a revolver under the right conditions.  This would
not happen with non-revolver pistols so the idea was the back
pressure wave when the bullet hit the forcing cone was a big
factor.   In rifles the pressure wave bouncing off the base of the
bullet idea was also suggested in other
sources, and the fact that there was little powder in the case to dampen
the waves was suggested as a cause.
I also wonder how progressive ball powders are.  Normally they would
be the opposite of progressive except for the coatings as you
mentioned.  I would still think they would not have a net progressive
burn rate.  If you have any sources on that, I'd be interested.
The only really progressive powders I know of are the tubular ones with
multiple holes through them, but don't know of any of these used
in rifles.
Also with the tubular IMR powders I don't think they vary the inhibitors
with powder speed, just the dimensions, except for 4831 the real
slow one.
Since ball powders occupy less volume than the IMR type, maybe the
case volume factor and the pressure wave idea contribute to the
phenomena.

Steve

From: sfaber@intgp10.ih.att.com (-Faber,S.R.)
Subject: Re: dangerous light loads
Organization: AT&T

The cause of the high pressures is most likely the effect of
the primer blowing the powder grains into the bullet base and case
shoulder, causing them to fracture and therefore become fast
burning powder.  There is always a certain amount of presure waves
bouncing back and forth, but with the case pretty empty, these would
not be damped out as much as with the case full, and with a full
case the powder would not fracture to as great an extent.
There were some pressure curves given in a recent Handloader that
show pressure spikes with a light load of powder shot when the powder
was settled to the base of the case before firing, and another curve
that showed lower more damped spikes when the powder was initially
toward the front of the case.  The article did not speculate on the
causes, but the data supports the above theory.  Besides someone
who works on developing tank ammo told me about that effect :).
If you keep in mind that burn rate is proportional to the pressure,
then one could imagine that a high pressure wave front could
build in amplitude sort of like the gain of a laser, but that
is just my analogy/speculation.