Evening star. [volume] (Washington, D.C.) 1854-1972, 1889-02-13
TESTING THE ssTHURLOw,' GUN.
Defects In the Cast-Steel 6-inch Breech
Loader.

II seems that the cast-steel 6-inch breech-
loading rife, known as the sThurlow" gun,
which apparently passed the government firing
tests successfully at Annapolis last week. lie not
going to have such an easy victory over the
hooped, or built-up cannon, after all. The
official report of the officer conducting the
tests mentions certain defects discovered in the
bore Of the gun that viii probably give ground
for final report adverse to its ACCEPTANCE by
the government. He will now proceed to ex-
anime the bore Of the gun in order TO deter
mine the size, number, and nature of the de-
fects. They are thought to be due to the gas
bubbles that formed during the casting pro-
cess. and the existence Of but one of them
would be sufficient to throw grave doubts upon
the reliability Of the weapon.
THE DEFECTS ALREADY DISCOVERED
exist about Sc inches from the breech Of the
gun, which has q total length Of Is feet. This
would place them just ''abaft the trunnions. :"
in the ordnance tongue, or one length ahead
Of the projectile % it lays in the gun before
firing.
A subsequent report, received at the Navy
department this morning, states that the de-
fects probably existed before the tests. and
were concealed by the discoloration Of the
ever, have been caused by the powder bursting
in the walls of the bubbles.
HOW HoLLows IN THE BORE OF A GUN ARE To-
GATED.
The operation Of examining the bore of the
gun is very interesting. 1t is not an easy mat
ter to get glimpse of the walls of tube Is
feet in length chat cannot be taken to pieces,
and SO an ingenious apparatus has been de-
vised that enables one not only to see the in
side of the gun, but to photograph it. 1t is
called an electric search rod, and consists of
an lncandescent electric lamp ON the end of a
long rod. few inches back of the lamp is a
mirror, at an angle of As degrees, facing from
the light. On the other end of the rod is a
telescope. The rod is thrust into the gun and
the electric current turned on. The light illu-
inmates the walls of the gun brightly,
and the rays are thrown back on the mirror and
reflected in horizontal line to the muzzle of
the gun, or the breech, according to which end
is selected. An eve at the telescope can thus
examine every inch of the interior surface, and
when suspicious spot is seen it is carefully
scrutinized. Then camera is substituted for
the telescope and a photograph taken of the
defect. This will show the spot as a darkened
place in the metal and does not give much of
an idea of its depth. In order to ascertain
this an impression of the hole is
TAKEN IN WAX
by means of another apparatus. First, how
ever, the spot must be exactly located, and in
order to do this rod bearing on its end
number of steel-spring rods springing out
ward with their points turned out is run back
and forth along the bore. When depression
is encountered one Of the points of the spring
rods catch and the manipulation of the rod feels
an obstruction to the progress of the brush.
The length from the muzzle is carefully noted
and marked, and another rod is then inserted,
CARRYING single steel piece with turned
point. This is run in the right distance and
turned around in order to catch the hole.
When it does this the operator can ascertain
the exact spot in the interior that
Is defective, by means Of measurements. Then
the impression apparatus is used. This con-
sists of a rod, conferred by blocks at intervals
along its length, provided with a wedge-shaped
piece, carrying on it an upright wooden rod
with lump of wax on its top. The wedge is
moved back and forth by means of another rod
parallel to the main one. When the exact spot
is reached, under which the wooden upright
falls, the wedge Is pressed back and the wax
forced up into the depression. The wedge is
then withdrawn and the whole apparatus re-
moved. The wax thus shows the exact nature
OF the hole. In this way the entire length of the
tube may be examined and the gun turned in
side out, as it were.
CAsT-srEEL VERSUS BuIT-uP GUNS.
Friends of the cast-steel gun are hopeful that
the defects noted will not cause the gun to be
rejected They say that it is only matter of a
short time before the cast-steel gun will entirely
replace the built-up, or hoped rifles, and that
the Thurlow gun shows that the requisite de-
gree of perfection in steel casting has been
reached. The cast gun is greatly cheaper than
the other, and takes about one-fourth as long
or less in construction