Controled test, re: accidental discharge, blamed on a stray ember. I thought that would not , could not, happen if the charge had been properly made, so devised an experiment.
My controled test was run last monday, in which I tried to determine how long it would take to ignite a black powder charge with a red-hot charcoal brickette, if protected by a charge casing constructed of only and exactly 2 layers of heavy duty kitchen foil.
I posted pictures in the SCA gunners list...3 pictures are in photos/kismet
http://groups.yahoo.com/group/SCA-Gunners/photos/album/564888360/pic/992084227/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc. One showing the setup - the shape of the
charges which were constructed, and the container, an alum. coke can bottom 1/3. I tested 2 charges in 2 cans at the same time, for two data points.
I wanted a metal container to keep the charge seated on the coal and the heat concentrated as it might in a gun tube. On the other hand I did not want to contain gases which might cause an explosion so the can was kept short.
The charge bottom is exactly 2-layers of heavy duty foil, using my cannon's(kismet's) charge shaper/mold(shaper pressed down into the center of a sheet, so that the bottom would not have any folds), and a half ounce of 1F
black powder (this was about a 1/3 inch thick powder layer), (goex-brand freshly opened can).
The second picture shows how the charge fits inside the container: about 90% close fit.
I removed 2 charcol bricketts from the middle of a pile on a grill, which were by my best judgement at peak heat. They had been heating about a half hour, and were fully ' ashed' and glowed a fairly uniform dull red. these were removed by thongs and placed in the 2 test containers. and within 20 seconds I put the
first charge on and 5 seconds later the second charge.
I noted the time and stood clear. The 3rd picture shows the test in progress.
After 15 minutes passed and neither charge had ignited, I terminated the formal
test, concluding that the coals had cooled and there was little prospect of
ignition. Nevertheless, for safety reasons I did not approach the test setup
until approximatly 40 minutes passed, at which time I lightly hosed down the
setup from a distance. 20 minutes later I approached the setup and poured on enough
water to fill the container, and found (somewhat to my alarm) that the coals
were still hot enough to boil the water I added and that the powder charge was
still being heated.
That's only two tests/trials, but I feel confident in concluding that 2 layers of foil well protect a charge from
accidental ignition from coals. In reality, an ember in a cannon would not be
nearly as large, hot and long burning as a charcol brick, and anyway it would
only need to protect the charge from igniting for a minute or so, to allow
completion of the loading process. I would like to repeat the test with a single layer of foil; would hypothesize that in all of several trials the charges would survive a minute without ignition (recalling all the times I applied a glowing slow-match to priming powder with no immediate effect).
A properly made foil-wrapped charge with not 2 but at least 3-4 layers of foil
seems essentially proof of any risk of accidental discharge by an ember. I don't
know what caused the accident, but it was not 'only' a stray ember.
-Rick Orli
