From: tip@lead.aichem.arizona.edu (Tom Perigrin)
Newsgroups: rec.org.sca
Subject: Re: period firearms
Date: 4 Jan 93 20:49:16 GMT
Organization: University of Arizona UNIX Users Group


While people are well advised to be concerned about the safety of
black powder weapons, I think I have seen some misapprehensions which need
to be addressed.

We should possibly distinquish between firearms FROM the period, firearms
made in the precise period fashion in modern times, and firearms which
look like period pieces except to close inspection.

Let me first discuss the concept of firing black powder in pieces
actually made pre 1600:   ICK!   What  horrible tragedy if the gun
explodes.   This should never be done.

Okay, now on to firearms made in the period fashion and firearms made to
look authentic:   The latter can be made quite strong, and yet look like
old pieces.  I have a 1580 style musket from Jakeman Arms, Worcester, UK,
which visually reproduces a musket shown in "Manual of Armes" by Jacob 
DeGhyn.    All of the parts are made in the 1580 style, with the small
exception of the barrel.   

The barrell is made from modern Bismuth Vanadium steel, and consists 
of two barrells inside of each other.  The outer diameter of 
the inner barrell is actually 0.01" larger than the inner dia of the outer
barrell.   The outer barrell must be heated to a red heat, and the water
cooled inner barrell forced into place.  When the outer barrell cools and 
shrinks it compresses the inner barrell, placing an inwards component of 
strain on the inner barrell.  Normally the stress resulting from internal
pressure in a tube is distributed from the inner wall
to the outer wall as a smooth 1/r^n fashion, with the stress maximized
on the inner wall and minimized on the outer wall.   But with a prestressed
barrell the force curve in an unpressurized tube actually changes sign, 
with a negative sign on the interior, zero somewhere in the middle, and 
positive on the outside.  When the powder explodes, the first force has to
overcome the prestress to bring the inner wall to zero.  The stress moves
radially outwards, utilizing the strength of the larger amount of metal
at greater distances from the bore.

Barrells for large guns are made this way.  Steel with a tensile strength of
100,000 PSI and YMI of 10^6  can be stressed safely to 80,000 PSI.
However, a increase to 120,000 PSI would allow for a increase of velocity
of nearly XXXXXX   (I don't have my book on internal ballistics here).
The increase in KE is substantial.   So barrells of large guns (howitzers,
navel guns, etc..) are made with up to 17 heat shrunk layers, giving a 
prestress of up to 40,000 PSI.

Obviously this technique is not inexpensive, but it increases the margin 
of safety substantially.   Jakeman's Arms are all tested by the British
Proof House, which tests them on static and kinetic testing modes.   Jakeman
also fires them with twice the BPH load himself.

Modern barrells are very strong.  I have a book which describes a series
of tests done with BV steel, CM steel, and other type sof steel barrells.
Tests were done in which 10* too much powder and 10 balls were loaded
into a barrell with no ill effect.   In fact, there is one test in which
the normal amount of powder was placed ina  barrell, and both ends were
sealed with threaded plugs... and all the pressure came out through the
vent hole.  (However, a double overload did blow it up).  Other tests
included sawing part way through the barrell, putting mud in the barrell,
forcing in the wrong sized ball, etc...   In all of these tests the margin
of safety was quite impressive, but failures could occur when the test
was severe enough (put 3* too much powder in, and pack the rest full of
mud).

Things which consistantly blow up black powder weapons are improper loading 
leaving an airspace btweent he powder and the ball,   using modern smokeless
powder, and allowing the barrel to corrode through lack of cleaning.  In 
addition, not all barrells are BV, CM, or other good steels.  Some cheap
and imported  barrells are made of soft steel, such as 1040.

Now 1040 is okay, if you know what you are doing.   My 2.5" bore, 7'
long cannon is 1040.  But the powder chamber has walls which are 2" thick!
And I use a coarse 1/4 mesh cannon powder to build a slow pressure rather then
the explosion that FF or FFF powder gives.   You can watch cannon powder
burn from one end of a pile to the other.   In fact, I have a paper passthrough
test which shows that some of teh powder is still burning when the
ball exits the cannon mouth.

A cannon barrel which has a calibre ratio of 0.6 or better (wall/bore) is okay
with 1040.  But my Jakemans Arms DeGhyn has a calibre ratio of 0.28,
thus it has to be made of high quality steels and prestressed.  My wheellock
has a calibre ratio of 0.45, which is a tolerable lower limit for a
BV unstressed barrell.    I would hesitate to overload my wheellock to the
same extent I might overload the Jakeman musket, because even though it
looks mroe substantial, it is actually weaker.   Thus, it would be important
to know WHO manufactured the weapon, and how.   This would imply some sort of
black powder marshallate.


This is exactly what is done in the Sealed Knot, where up to 1000 people
with muskets get out onto the feild and actully point them in each others
direction!!!!!!!!!!!!!!!!!!

Blowing up is not a consideration,  but flying ramrods are.   THere is
a rigourous training that musketeers must go through, and a rigorous
test before you can get your card.  I have set this up at the Arizona
Rennaisence festival, and we shoot off cannons, mortars, muskets, and other
weapons 5 times per day for 12 days, and have never had an accident in 5 years.
(We did lift the King's skirts once, but's thats another story *grin*).


So, to summarize...   black powder weapons can be safe, if made and handled
properly.   Authentic museum peices, and pieces made in the period fashion
are not safe enough.  But pices made of modern materials made to look
appropriate have margins of safety well beyond that of driving to the event.

If black powder is to be a part of the SCA, they should learn from 
organizations which use BP a lot (Sealed Knot, American Civil War), and
implement an BP marshallate.   I would be willing to help set up and
serve on such a committee.
From: Longshot@f19.n291.z1.fidonet.org (Longshot)
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