Newsgroups: rec.pyrotechnics
From: ahahma@utu.fi (Arno Hahma)
Subject: Re: Pistol Powder, can it...
Message-ID: <ConD0s.ADJ@utu.fi>
Date: Fri, 22 Apr 1994 06:07:40 GMT

In article <125.1570.60.0N3F6C10@irs.com>, Hoss Topper <hossie@irs.com> wrote:

<about low charge detonation in firearms>

>spread out along the bottom of the case with a lot of airspace left above
>it, it can -- sometimes -- detonate or at least burn MUCH more rapidly

In fact, it will burn too slowly at the beginning. Later on, the powder
burns very fast.

>According to ammunition and powder companies, the mechanism is not yet
>fully understood.  Meanwhile, reloaders are advised to use

How come? In think the mechanism isn't that difficult at all to
understand. If you have a too light load unevenly spread in the case,
the charge will ignite partly, slowly or not at all because of too low
a pressure, too weak a primer or uneven distribution of the flame
across the powder volume. Then the bullet may start decelerating or
even stops in the barrel.

Should that happen, the gases behind the bullet stagnate and the
pressure and temperature rise sharply at the bullet base. As the powder
charge always moves with the bullet, the powder starts burning rapidly
at the bullet base (local pressure peak) and amplifies the pressure
peak.  Next, the pressure peak will start traveling towards the bolt in
the barrel and reflects back at the case bottom (bolt face). All the time,
the pressure wave gains more and more energy from the powder spread
along the case and the barrel behind the bullet. When this oscillation
reaches high enough amplitude, it turns into a shockwave, i.e. a
detonation (powder is still present to provide the shockwave with
energy).

Such a small charge detonation is always preceded by several pressure
peaks (can be seen in a test barrel with pressure transducers) until
the peaks reach very high pressures and all of the powder still left
burns with a single pass of the wave, which indicates a real
detonation.

>fast-burning pistol powders in squib loads for large-cased rifle calibers.

Pistol powders (especially the porous types) ignite easier than coated
rifle powders. In addition, it is best to use as strong a primer as
available for those light loads to ensure proper ignition of the
powder. Also, as pistol powders burn faster, the pressure rises high
enough for stable burning and for keeping the bullet under acceleration
until the powder burns out.

Using pistol or other easily igniting and fast burning propellant is
the correct procedure to avoid a low charge detonation. A filler also
helps, as the powder charge is kept close to the primer and ignites all
at once.

BTW, revolvers are particularly prone to low charge detonation, as the
bullet hits the lands hard and always decelerates strongly.

>george.willard@f66.n286.z1.fidonet.org

ArNO
    2