162 
POPULAR SCIENCE REVIEW. 
in their normal state vary from a state of compression within to 
tension without ; each part thereby hearing its own work — that 
is, when the strain comes on it, the whole thickness of the gun 
is serviceable in resisting' it. 
We have now to consider the projectile. Windage, or the 
looseness of the bullet in the bore, for ease in loading, has 
been before adverted to, with the inaccuracies to which it gives 
rise. In the rifle, where the spherical bullet was used, there 
was necessarily no windage, for the bullet, in order to take 
the grooves, was (except in the two-grooved rifle with belted 
ball) forced down by a heavy ramrod and mallet. This difficulty 
in loading was, indeed, one of the main objections to the rifle. 
Breech-loaders and expanding bullets afford means of avoiding 
windage and yet loading’ easily. 
The methods by which the modern cylindro-conical projectile 
is made to take the rifling, or fit the grooves of the gun, may 
be classed under three heads : — 
1. The mechanical fit, where the projectile is made of the 
exact form of the bore before being inserted in it. The pro- 
jectile may be of hard metal throughout. This plan has heen 
adopted by Mr. Whitworth, Mr. Lancaster, Captain Blakeley, 
and others, in Engl and, and in all the foreign ordnance we 
have seen. 
2. By making the projectile (which must, therefore, be at 
least coated with a soft metal) rather larger than the bore 
of the gun. It is inserted at the breech, which is enlarged 
to receive it, and it takes the rifling by being forced forward 
by the powder and crushed into the grooves. This plan is 
adopted by Sir William Armstrong,* and. also in many breech- 
loading small-arms. 
3. By the projectile, which is of some soft metal, as lead, 
and is small enough to be loaded at the muzzle, being made to 
expand into and take the grooves by the explosion of the powder. 
The projectile, then, generally has a hollow at the base, in which 
a wooden or iron plug is inserted. This having less specific 
gravity than the lead, is driven forward by the discharge, and 
expands the bullet. It is found also, that when the projectile 
is proportionately rather long, the hollowed base, either with 
or without a plug, is unnecessary; the expansion takes place 
sufficiently without it, from the explosion acting’ in the manner 
of a blow, and forcing the base of the cylinder forward before 
the front has had motion communicated to it. This plan, 
though very generally adopted for small-arms, has never suc- 
ceeded with ordnance. In small-arms it is very generally 
* Sir W. Armstrong has, however, made some of his large guns muzzle- 
loaders, on the shunt principle, which is of the nature of a mechanical fit. 
