164 
SHORT NOTES ON THE 13-PR. M.L. GUN. 
Choke. 
Rifling. 
Vent. 
Sights. 
reduction of density which, enables us to fire the comparatively large 
charge of the gun, 3 lbs. 4 ozs. 
The great length of the cartridge, and its being of R.L.Gr . 2 powder, 
which burns more slowly than R.L.Gr., necessitates (1) an increased 
length of bore, and (2) centre-venting, in order that it may be entirely 
consumed. 
To ensure regularity of shooting, it is necessary that the density of 
the charge should always be the same. To effect this the projectile is 
prevented from entering the chamber by a choke, or concentric con¬ 
traction of the bore for about 3 ins., having a slight incline on either 
side. In loading, the gas-check of the projectile coming in contact 
with the front incline is brought up at the same point each round; in 
addition to this the choke closes all windage. 
The rifling is poly groove, and consists of ten shallow grooves. This 
system distributes the strain round the bore at a great number of 
points, and the gun is weakened to a far smaller extent than in the 
old system. The form of groove is symmetrical, the loading and 
driving sides being alike; the twist, uniformly increasing from 1 turn 
in 100 in front of the choke to 1 in 30 at 9 ins. from the muzzle, 
then remains uniform at 1 in 30 for the remainder of the bore. There 
is therefore a very small initial strain on the gun due to rifling, and 
the projectile is steadied on leaving the muzzle. 
The vent-bush is fitted by hand, and filed down roughly to get rid 
of the troublesome process of cutting it off flush, and consequently 
a small portion is left projecting into the bore. 
To enable the cartridge to be ignited near the centre, the vent is 
placed 7 ins. from the end of the bore. This position of the vent leads 
to a considerable amount of residue being left in the chamber, 
especially when blank charges are used. Careful watch should there¬ 
fore be kept that danger does not arise, especially as the sponge, 
having to pass the smaller bore and choke, must be of very low gauge 
compared with the chamber. 
The system of sighting is new ; it consists of— 
1. A tangent scale, nearly the same as the service pattern, having 
in the leaf an ordinary notch, *06 in. deep, protected by rising planes 
on each side. Below this is a cupped recess, having in its centre a 
small hole, *05 in. in diameter, for fine sighting. 
2. A bronze block, with keep-pin fitting into a slot in the dispart 
patch. This block is furnished (a) with a fore-sight of bronze in the 
form of a point, for rough laying in conjunction with the notch of the 
tangent scale, (b) with a reading window and cross-wires, for fine laying 
in conjunction with the eye-hole. 
The sights are not as yet inserted at an angle to correct permanent 
deflection, nor are the bars of the tangent scales marked with ranges 
in yds. and lengths of fuze, owing, no doubt, to the fact that modifica¬ 
tion might be found to be necessary, either in charge or projectiles, 
during or after the trials, and before the actual adoption of the gun 
into the service. 
