As R.M.L.s became larger and their shells became heavier it was necessary to find a way of loading them so that the studs could be engaged with the grooves in the barrel, not an easy task. The solution was the muzzle derrick.
From the 1877 and 1879 ‘Treatise on the Construction of Ordnance’: A fitting is now provided for the 9-inch L.S. Guns and upwards for purpose of raising the projectile to the muzzle of the piece. It is used only for guns not mounted behind iron shields. It is made of bronze and consist of a band (A) and derrick (B) as by the drawing. The band is fixed round the chase of the gun at a distance of from seven to twelve inches from the muzzle, according to the nature of the gun and the derrick is secured to it by two screw bolts. The derrick has a ‘bridge piece’ (b) which rests on the top of the chase, supporting the fore part of the derrick, which projects over the muzzle the amount required for convenience of loading. To the loop (c) would be hooked the single block of the small tackle by means of which the projectile is raised. The band when adjusted in the proper position is secured to the gun by four screws. Instructions for adjusting and securing these derrick bands are as given:
Instructions to be observed in fixing bronze derricks to muzzles of heavy rifled guns :
1st Scribe a line upon the top of the chase from the vertical axis line on muzzle for a distance of about 12 inches towards the fore sight
2nd. Remove the filing screws and then try on the band ; there may be a slight variation in the diameter of the muzzles of guns of the same nature, but if they are correct the bands would be seated as follows, viz.:-
Distance from face of muzzle to font for 9” M.L. guns 5½” ;
edge of band for 10”, 11”, 12”, and 12½” guns, 6”.
Should the band not reach its seat, it will be necessary to ease it inside with a half-round file until it attains the required position. If, on the other hand, the muzzle of the gun be small, the band must be pushed on as far as it will go.
3rd. When the band has been placed roughly in its position, turn it round until the vertical lines cut on the front and rear faces agree with the scribed line on muzzle mentioned above. When properly adjusted, give the front edge a few gentle tape all round with a piece of wood to drive it on the chase, and thus fix it temporarily in position, but the relations of the lines must not be disturbed in so doing.
4th. Now mark off upon the chase the positions of the holes by means of a steel scriber carefully guided around the interior of the screw holes, and then remove the band. Special attention must be paid to this operation.
5th. Dot round with a centre punch the circles just described, and centre each as nearly as possible ready for drilling.
6th. Erect the drilling apparatus and drill very carefully four holes, each 8/10 in diameter and ½ deep, to correspond with the plain points of the fixing screws.
Judgment must be exercised in drilling the holes if required, so that they may be perfectly concentric with the dotted circles previously marked off.
At the chief stations, where artificers are at hand, drills can readily be prepared on the spot for this purpose, but in localities where these conveniences do not exist, the drills can be supplied on demand.
7th. After the holes are completed remove the drilling tackle, clean the surface of the chase, take off all burrs from the holes, and place the band in position; then insert the screws and send them home firmly and securely.
It will be necessary to adjust the bridge piece which supports the derrick when erected, so that the latter may be brought forward in order to maintain the required relation with the muzzle of the piece. It will be requisite first to level the gun and then to drop a plumb-line from the centre of the loop or eye at the top of the derrick, and the distance measured from the face of the muzzle to this line should be-
For 9” M.L. gun 7.4
12” 25-ton 10.45
Limits of error, one inch minus or plus.
Where the measurement does not comply with the above dimensions, the lover side of bridge piece must be cut away and relieved until the proper overhang has been obtained.
Fort Scratchley 9-inch R.M.L. drill with the Muzzle Derrick
A 9-inch RML at Fort Scratchley with the muzzle derrick thrown back after loadiing
The derrick ready for lifting the projectile
Raising the projectile using the derrick
Ready for the next projectile
From the Handbook for 9-inch R.M.L. Guns:
MUZZLE DERRICKS, MARKS I TO V GUNS.
Muzzle derricks are provided for raising the projectile to the muzzle, except in the case of guns mounted in casemates, behind shields, on high-angle mountings, or where the emplacements are
provided with sunken ways and slide derricks. They are made of
bronze, and consist of a band fixed round the chase at about 7 inches from the muzzle and a derrick secured to the band by two bolts. The derrick has “bridge-piece” which rests on the gun supporting the upper part of the derrick which projects over the muzzle. The tackle should be hooked into the eye at the top with the back of the hook towards the gun, and the point through the loop to prevent the tackle from slipping. The band is secured to the gun by four screws, two in the vertical and two in the horizontal axial plane of the gun. The derrick should be turned back on the chase after loading, and always kept there when not actually in use.
During the drill:
To Load: Nos 4 and 5 raise the derrick. After the projectile has been rammed home No 4 throws back the derrick. No5 makes up the fall and lays it on top of the gun. With the 12.5-inch R.M.L. he places the coil on the left trunnion stud.
R.M.L. at Fort Largs: with muzzle derrick
10-inch R.M.L. at Puckpool Battery: with muzzle derrick
10-inch RML at Inchkeith showing the muzzle derrick
12.5-inch RML with muzzle derrick at The Verne