THE ROYAL ARTILLERY INSTITUTION. 
351 
T). 2.—Experimental, No. 91 (1861). 12-pr. breech-loading gun, of 
calibre; weight, 9 cwt. 3 qrs. 
This gun has fired 144 rounds of shot. Mr Whitworth has been authorized 
to supply shells, for which the Committee are waiting. 
3. It will be seen from the foregoing statement, that the evidence before 
the Committee is unfavourable to the safety of Mr Whitworth's system, as 
applied to either cast-iron or homogeneous-iron guns of large size, and it will 
be evident from a consideration of the system itself, that it must throw an 
extraordinary strain on the gun. 
4. The peculiarities of this system consist in— 
(a) Polygonal rifling; 
( b ) Small calibre, or somewhat more elongated projectiles than 
usual; 
(c) Yery rapid twist; 
( d ) Extremely perfect finish, and mechanical nicety of fit in the 
projectile. 
The Committee are not aware of any mechanical superiority of the poly¬ 
gonal system of rifling over other systems, supposing them all to be executed 
with equal precision. It has the disadvantage of presenting six lines of 
reduced strength along the whole length of the bore, against which a violent 
rending action is exerted by an unyielding projectile. The absence of wind¬ 
age in the guns first made, and the extreme precision of fit attained, rendered 
the operation of loading also a difficult one, the projectile being very apt to 
stick in the bore; this has been partially remedied in the guns of later 
manufacture, by an alteration in the form of grooving; the sides of the 
polygon are now no longer plane, but the precision of the gun appears 
still to depend very much upon closeness of fit, which the Committee 
consider that* it would be difficult to maintain. Iron projectiles cannot be 
guarded entirely from rust; the bearing surfaces would require to be cleaned, 
and painted from time to time. If originally planed and finished with the 
nicety hitherto applied to them, they would be liable to vary in diameter by 
the effect of rusting, scraping, and painting, so that some of them would 
probably not go home in the bore. If not so finished, but left with a 
moderately easy fit, calculated to allow for these contingencies, the gun 
forfeits one of its principal claims to superiority. 
5. A small calibre, or preference for elongated projectiles, may be called 
another distinguishing feature of Mr Whitworth's rifled-cannon system, 
although in this respect the difference is not so great between his projectiles 
and the Armstrong projectiles, as it is between his rifle bullet and the Enfield 
bullet. His 12-pr. shot are 3*4 calibres in length. Sir Wm. Armstrong's 
being only 2*3 calibres long. The average of nine sorts of hollow shot 
and shells gives a length of 3 calibres, and some of them are as long as 
