From: ahahma@polaris.utu.fi (Arno Hahma)

In article <1991Nov8.020210.1224@cis.ohio-state.edu>
rubin@chocktaw.cis.ohio-state.edu (daniel j rubin) writes:

>BP IS BETTER in the things you have mentioned above.  All I know is that when
>I used Pyrodex to launch a approx 2" shell from about a 2' mortor it did not

BP is better for launching a shell in this case. You say: "about 2" " -
that is exactly the reason why pyrodex does not work. With "precisely or
very close to 2" " it would be much better.

Internal ballistics of guns is a large area to explain in a single
article :-). Anyway, I try to give some information without too much
differential equations ,->. 

>think Pyrodex would do diddly in Cannons and the other things you mention 
>above.  That is why they use BP.

It works just fine as long as the projectile is heavy enough and the
fit is tight enough.


Demonstration #1:

  >get that much altitude and really didn't even have a powderful sounding burn
  >( it is kinda hard to explain what I mean here, but you can just tell the 
  >difference in the launch when you use BP and Pyrodex by the WHOOOSH of the 
  >launch ).  The shell was a very tight cylindrical shell.  BP seems to even


>  Daniel Joseph Rubin    |


In article <8NOV199112142791@ubvmsc.cc.buffalo.edu>
v064myby@ubvmsc.cc.buffalo.edu (Christophe J Quaranta) writes:

Demonstration #2:

  >	I stated in a previous post that Pyrodex has a slower burning rate
  >when unconfined than commercial BP.  This can be demonstrated simply by 
  >pouring a small amount on a flat surface and igniting.  Black powder goes
  >off with a whoosh, while Pyrodex makes more of a shhhh sound.  

Both of the demonstrations here, the one with the loose fitting mortar
and the especially the open burn test indicate the burning
characteristics of pyrodex quite clearly and also explain, why it does
not work with the mortar as described.

>	However when confined, as in a mortar tube or gun breech, the two
>should have nearly the same burning characteristics.  I'm going to give it
>a try, because I'm sure you could get Pyrodex to work in a mortar.  

Yes, it is possible - use a tight fit or multiple charges (look at the
end to see what I mean).

>						Chris Q.
>						Buffalo, NY

Some views to the internal ballistics of BP and pyrodex in a gun:

First, let`s assume both pyrodex and BP have the same vividity - at
least they are close, since both the powders are interchangeable in a
gun, this is also stated in the patent.

The vividity is always measured under a high pressure, under
conditions in a gun or in a manometric bomb. This is feasible, since
the guns operate at high pressures and all of the powder is burning.
However, the vividity tells absolutely nothing about the ignition
properties and development of the burn of the powder, it is only a
measure of the linear burning rate of the powder. Thus, powders with
the same vividity can burn very differently in the open or under a low
pressure and yet function exactly the same way in a gun.

The reason why BP is the best propellant for low pressure
applications, loose fits like mortars, is its unique ignition
property. The linear burning rate of BP is low, compared to almost any
modern smokeless powder, that is why the barrels of BP guns are long.
On the other hand, the surface propagation rate is almost infinite
compared to any of the same powders making BP ideal for developing
pressure regardless of confinement. Only some whistle mixes and flash
powder have better surface propagation rates. They are not used, since
the burning is quite subject to developing into a detonation - no
wonder since the surface propagation itself is pushing the limits of
deflagration already.

As a result, if you ignite BP in the open, the whole mass will ignite
practically simultaneously, despite of an ignition at a single point
only (look at the demonstration #2). In the mortar, this is what you
always wish, to get the pressure high to a desired level as quickly as
possible, even with a loose fit. With pyrodex, the burn propagates
more or less as a front under low pressure.  Igniting this type of
powder at one point in a mortar causes the burn to develop slowly, the
shell starts travelling keeping the pressure low and preventing the
burn from accelerating enough. This is especially true if the fit is
loose and the initial loading density is low. Before you even reach
the desired pressure level, the shell already exits with only a little
velocity leaving much powder behind still burning in the tube
(demonstration #1).

This is also the problem in cannons and guns. With cannons, the
projectile is not tightly fit to the tube before its band squeezes into the
rifles or tube. The pressure won`t build up easily and a complicated ignition
system is required, surprise, surprise, most often loaded with BP.
With handguns the problem is solved differently, the bullet is tightly
compressed and glued to the casing causing the pressure build up enough to
accelerate the burning of the powder. As the bullet does get loose the
pressure is already very high and the powder is burning at high enough
rate to sustain the pressure.

There are basically two solutions with the mortar to overcome the
problem with pyrodex. One is to use a tight fit. This might give the
powder enough time to ignite thoroughly and develop enough pressure to
burn completely before the shell exits. Pyrodex is a pyrotechnical
mixture, so this might work. The other and better method is to ensure
a thorough, simultaneous ignition by using a good ignitor instead of
just a match.  This could be done with a bag of BP or even flash type
powders. Simply make a double charge, a small one with BP and the main
charge of pyrodex.  This is also the approach used with the real
cannons, there are at least two types of powder in the charge, a fine
one for developing the pressure at the beginning and pushing the
projectile into the tube or at least for ignition and a second one for
sustaining the pressure while the projectile is travelling in the
tube. With a single powder this is next to impossible, unless BP is used.

This would also allow the use of smokeless powder for shell lift. Some
smokeless powders (shotgun and pistol powders) burn fast and their
burning also accelerates fast, i.e. you need little pressure. A mortar
powder would be ideal, it has been designed to lift a loose fitting
projectile even with a very low loading density.

Pyrodex, like BP, is a mechanical mixture of oxidizers with fuels,
actually, it is a mixture of BP and a whistle mix. The patent gives an
example with potassium nitrate, sulphur, charcoal, potassium
perchlorate, sodium salicylate, dicyandiamide, wax and wetting agents.
In addition to this, pyrodex contains several per cent of water. The
water content probably explains, why pyrodex has a much lower surface
propagation rate of the flame than BP. Also, the dicyandiamide 
certainly slows down burning and makes ignition slower.

I hope this helps. Also, I would be interested to hear, if someone
experiments with pyrodex, if a shell can be launched with it. If it
can, the stresses on the shell would probably be more uniform and
lower than with BP.

ArNO
    2

_______________________________________________________________________________
_____  _____  _____
|   |__|   |__|   |           A. Hahma
|                 |           Research Centre of the Defence Forces
|_________________|           Department of Chemistry
 |       .       |            Laboratory of Propellants and Explosives
 |   .       .   |            BOX 5
 |       .       |            SF-34111 LAKIALA
_|   .       .   |_           Tel. +31-492177
|        .        |          
|                 |
|_________________|

From: ahahma@polaris.utu.fi (Arno Hahma)
Newsgroups: rec.pyrotechnics
Subject: Re: Pyrodex chemical composition
Message-ID: <1991Nov14.194427.13737@polaris.utu.fi>
Date: 14 Nov 91 19:44:27 GMT

In article <1991Nov8.020210.1224@cis.ohio-state.edu>
rubin@chocktaw.cis.ohio-state.edu (daniel j rubin) writes:

>BP IS BETTER in the things you have mentioned above.  All I know is that when
>I used Pyrodex to launch a approx 2" shell from about a 2' mortor it did not

BP is better for launching a shell in this case. You say: "about 2" " -
that is exactly the reason why pyrodex does not work. With "precisely or
very close to 2" " it would be much better.

Internal ballistics of guns is a large area to explain in a single
article :-). Anyway, I try to give some information without too much
differential equations ,->.

>think Pyrodex would do diddly in Cannons and the other things you mention
>above.  That is why they use BP.

It works just fine as long as the projectile is heavy enough and the
fit is tight enough.


Demonstration #1:

  >get that much altitude and really didn't even have a powderful sounding burn
  >( it is kinda hard to explain what I mean here, but you can just tell the
  >difference in the launch when you use BP and Pyrodex by the WHOOOSH of the
  >launch ).  The shell was a very tight cylindrical shell.  BP seems to even


>  Daniel Joseph Rubin    |


In article <8NOV199112142791@ubvmsc.cc.buffalo.edu>
v064myby@ubvmsc.cc.buffalo.edu (Christophe J Quaranta) writes:

Demonstration #2:

  >	I stated in a previous post that Pyrodex has a slower burning rate
  >when unconfined than commercial BP.  This can be demonstrated simply by
  >pouring a small amount on a flat surface and igniting.  Black powder goes
  >off with a whoosh, while Pyrodex makes more of a shhhh sound.

Both of the demonstrations here, the one with the loose fitting mortar
and the especially the open burn test indicate the burning
characteristics of pyrodex quite clearly and also explain, why it does
not work with the mortar as described.

>	However when confined, as in a mortar tube or gun breech, the two
>should have nearly the same burning characteristics.  I'm going to give it
>a try, because I'm sure you could get Pyrodex to work in a mortar.

Yes, it is possible - use a tight fit or multiple charges (look at the
end to see what I mean).

>						Chris Q.
>						Buffalo, NY

Some views to the internal ballistics of BP and pyrodex in a gun:

First, let`s assume both pyrodex and BP have the same vividity - at
least they are close, since both the powders are interchangeable in a
gun, this is also stated in the patent.

The vividity is always measured under a high pressure, under
conditions in a gun or in a manometric bomb. This is feasible, since
the guns operate at high pressures and all of the powder is burning.
However, the vividity tells absolutely nothing about the ignition
properties and development of the burn of the powder, it is only a
measure of the linear burning rate of the powder. Thus, powders with
the same vividity can burn very differently in the open or under a low
pressure and yet function exactly the same way in a gun.

The reason why BP is the best propellant for low pressure
applications, loose fits like mortars, is its unique ignition
property. The linear burning rate of BP is low, compared to almost any
modern smokeless powder, that is why the barrels of BP guns are long.
On the other hand, the surface propagation rate is almost infinite
compared to any of the same powders making BP ideal for developing
pressure regardless of confinement. Only some whistle mixes and flash
powder have better surface propagation rates. They are not used, since
the burning is quite subject to developing into a detonation - no
wonder since the surface propagation itself is pushing the limits of
deflagration already.

As a result, if you ignite BP in the open, the whole mass will ignite
practically simultaneously, despite of an ignition at a single point
only (look at the demonstration #2). In the mortar, this is what you
always wish, to get the pressure high to a desired level as quickly as
possible, even with a loose fit. With pyrodex, the burn propagates
more or less as a front under low pressure.  Igniting this type of
powder at one point in a mortar causes the burn to develop slowly, the
shell starts travelling keeping the pressure low and preventing the
burn from accelerating enough. This is especially true if the fit is
loose and the initial loading density is low. Before you even reach
the desired pressure level, the shell already exits with only a little
velocity leaving much powder behind still burning in the tube
(demonstration #1).

This is also the problem in cannons and guns. With cannons, the
projectile is not tightly fit to the tube before its band squeezes into the
rifles or tube. The pressure won`t build up easily and a complicated ignition
system is required, surprise, surprise, most often loaded with BP.
With handguns the problem is solved differently, the bullet is tightly
compressed and glued to the casing causing the pressure build up enough to
accelerate the burning of the powder. As the bullet does get loose the
pressure is already very high and the powder is burning at high enough
rate to sustain the pressure.

There are basically two solutions with the mortar to overcome the
problem with pyrodex. One is to use a tight fit. This might give the
powder enough time to ignite thoroughly and develop enough pressure to
burn completely before the shell exits. Pyrodex is a pyrotechnical
mixture, so this might work. The other and better method is to ensure
a thorough, simultaneous ignition by using a good ignitor instead of
just a match.  This could be done with a bag of BP or even flash type
powders. Simply make a double charge, a small one with BP and the main
charge of pyrodex.  This is also the approach used with the real
cannons, there are at least two types of powder in the charge, a fine
one for developing the pressure at the beginning and pushing the
projectile into the tube or at least for ignition and a second one for
sustaining the pressure while the projectile is travelling in the
tube. With a single powder this is next to impossible, unless BP is used.

This would also allow the use of smokeless powder for shell lift. Some
smokeless powders (shotgun and pistol powders) burn fast and their
burning also accelerates fast, i.e. you need little pressure. A mortar
powder would be ideal, it has been designed to lift a loose fitting
projectile even with a very low loading density.

Pyrodex, like BP, is a mechanical mixture of oxidizers with fuels,
actually, it is a mixture of BP and a whistle mix. The patent gives an
example with potassium nitrate, sulphur, charcoal, potassium
perchlorate, sodium salicylate, dicyandiamide, wax and wetting agents.
In addition to this, pyrodex contains several per cent of water. The
water content probably explains, why pyrodex has a much lower surface
propagation rate of the flame than BP. Also, the dicyandiamide
certainly slows down burning and makes ignition slower.

I hope this helps. Also, I would be interested to hear, if someone
experiments with pyrodex, if a shell can be launched with it. If it
can, the stresses on the shell would probably be more uniform and
lower than with BP.

ArNO
    2

_______________________________________________________________________________
_____  _____  _____
|   |__|   |__|   |           A. Hahma
|                 |           Research Centre of the Defence Forces
|_________________|           Department of Chemistry
 |       .       |            Laboratory of Propellants and Explosives
 |   .       .   |            BOX 5
 |       .       |            SF-34111 LAKIALA
_|   .       .   |_           Tel. +31-492177
|        .        |
|                 |
|_________________|