THE EOYAL AETILLEEY INSTITUTION. 
389 
A great many points of considerable importance must be borne in 
mind in considering the value of these different systems of rifling. 
The first, and not the least, is the effects they have on the strength of 
the gun. Those which cut deep grooves are most detrimental in this 
respect, and thus far the Austrian experimental gun has an undoubted 
superiority; for not only are the grooves shallow, but—what is of much 
more importance—they are many and broad. One groove in the bore of 
a gun injures the gun much more than fifty ; for we must not only pro¬ 
vide for the strength, but also for the stretch of the bore. If there be 
only one groove, the whole stretch tends to come on that part, because 
it is weakest and yields most readily. It is the same principle which 
has been successfully avoided by Sir William Palliser, in making the 
body of his bolts less, in diameter than the weakest parts of the thread, 
so that the stretch comes on the body which is long rather than on the 
shallow part of the threads, which are comparatively very short. The 
defect of this law was also discovered and early avoided in the Royal 
G-un Factories, by not cutting the thread for the breech-screw deeper 
into the breech-piece than that part which received the steel tube. No 
other system avoids this objection ; for we find they all cut grooves 
into the bore of the gun, and thus injure it more or less. Even 
Whitworth's hexagonal system of rifling is a grooved system in this 
respect. 
Those systems which have most grooves are, however, to be preferred 
to those which have fewer; and the fact that the Norwegian system 
has a double number of grooves is rather an advantage than a disad¬ 
vantage. 
In connection with the effect any system of rifling has on the 
strength of the gun, a most material point is the windage given. A very 
small increase of the amount of powder consumed causes also a very great 
increment of pressure, and a very small amount of windage gives a 
corresponding relief. This is a difficult problem, for windage is 
the main cause of the scoring and destruction of the guns at present 
in the service. The only escape out of the two objections is to stop 
the windage over the body, and give it through the interior of the 
projectile, utilizing it at the same time to ignite the fuze. Lead-coating 
effectually stops windage, advantageously or disadvantageously; and in 
this respect is superior or inferior to all other systems, according to the 
circumstances of the case. It is possible to stop windage in all guns 
by the use of an expanding wad, which would thus render them all 
practically equal in this respect. 
It remains now to consider the strain and friction on the surface of 
the projectile, and on the grooves of the gun. The easiest way of 
doing this is to compare the amount of force required to produce 
rotation with that to produce translation, and also the friction of the 
shot along the bore. 
Let x — the distance travelled by the shot in the time t , 
6 = the angle of rotation described in the same time, 
P = pressure producing translation, 
p — ,i ,i rotation. 
