Chapter XI: Specifications for British Combination Time and Percussion Fuses

The following specifications, abstracted from the official requirements relating to British “Mark I” (No. 85) combination time and percussion fuses, give the general information required in the manufacturing and inspection of these fuses. These specifications, in conjunction with the very complete illustrations, Figs. 1 to 6, inclusive, of the design and details of the British fuse, give all the essential data required.

=Components.=--The fuse consists of the following parts: Body, top and bottom composition rings; cap with set-screw; base plug with screw plug; time detonator pellet in two parts; percussion pellet with sleeve and firing pin; detonators; four spiral springs; brass and steel pins; onion skin paper; unbleached muslin; felt cloth and brass washers; brass and tin-foil disks; suspending ring for time pellet; and onion skin paper patches.

=Metals.=--The body and composition rings are to be made of bronze or metal known as “Class B;” the time detonator pellet and percussion pellet to be of hard-rolled brass; the percussion firing pin pivot, of steel, phosphorized or blued; the time and percussion firing pins, of bronze or “Class B” metal; all other parts of the fuse, except where otherwise stated, of metal “Class C,” or hard-rolled brass. The contractor must supply the necessary metal for testing, free of charge.

Metals designated by “classes” are copper alloys, the compositions of which are left to the discretion of the makers providing the metals conform to the above tests.

Before proceeding to manufacture, the material must be submitted to the inspecting officer for mechanical test. When practicable, test pieces should not be less than 7 inches in length nor less than 1 inch in diameter, and will be required to stand the following minimum tests:

+------------------+--------------------+-----------------------------+
| | Tenacity, Tons per | Elongation in Per Cent in |
| | Square Inch | such a Test Piece as can |
| Metal +---------+----------+ be furnished, provided |
| | Yield | Breaking | that |
| | Point | Stress | Length / √Area = 4 |
+------------------+---------+----------+-----------------------------+
|Bronze | 13.5 | 27 | 20 |
|Class “B” | 12 | 20 | 30 |
|Class “C” | 6 | 12 | 10 |
|Hard-rolled Brass | 6 | 12 | 10 |
+------------------+---------+----------+-----------------------------+

=Body.=--The body is to be turned all over, and threaded externally at the upper and lower ends, a bevel being formed at the junction of the stem and the flange. The stem is to be bored, and a hole drilled at the bottom of the bore to receive the time firing pin. The upper surface of the flange is to be grooved. The interior is to be bored out to form a chamber for the reception of the percussion arrangement and threaded for the base plug; a hole is to be bored and threaded at the bottom of the bore to receive the percussion detonator holder. An annular recess is to be made for the magazine. Communicating holes are to be drilled as follows:

(a) At an angle to the top surface of the flange.
(b) Vertically from the magazine recess.
(c) Horizontally at the top of the detonator recess.
(d) At an angle to join (b) and (c).
(e) At an angle from outside to bottom of recess in stem.

Holes (c) and (d) are to be closed by plugs driven in and secured by punch stabs. Two slots are to be cut in the flange as shown in Fig. 2, and an elongated hole made to receive a stop pin, which is to be secured by a small pin, driven in. A setting mark is to be cut on the edge of the flange.

=Top Composition Ring.=--The ring is to be turned all over, and bored to fit the stem of the body. A groove is to be formed in the under side for the composition, and a recess made as shown in Fig. 2, three holes being drilled from the upper surface into the recess. A hole is to be drilled through the ring between the ends of the composition channel, and recessed. A recess is to be formed in the bore, from which a flash hole is to be drilled at an angle communicating with one end of the composition channel, a vertical escape hole being made from the top surface to the flash hole. An indicating mark is to be made on the outside of the ring. Two holes are to be bored between the ring and the stem of the body, into which pins are to be inserted to retain the ring in position. The ring is to be made 0.020 inch thicker than the dimension given on the drawing, and faced off to thickness after powder is pressed into the groove.

=Bottom Composition Ring.=--The ring is to be turned all over and bored to fit the stem of the body, the upper surface being grooved. A groove is to be formed in the under side for the composition, and an annular recess made, three holes being drilled from the upper face into the recess. A hole is to be drilled in the ring from the under side between the ends of the composition channel. An escape hole is to be drilled, at an angle, from the end of the composition channel to the annular recess, and a recess made to receive the closing disk. A hole communicating with the groove and the escape hole is to be drilled at an angle to the top surface to receive a powder pellet. A hole is to be drilled and recessed for a setting pin, which is to be secured by a small pin driven in. The ring is to be graduated from “0” to “21.2;” each division, after the first, is to be sub-divided into five parts. A line to denote safety position is to be marked. The marking is to be blackened with japan black thinned with spirits of turpentine, except the mark denoting the safety point, which is to be colored red.

=Cap with Set-screw.=--The cap is to be machined all over, and recessed internally to receive the time detonator pellet. The lower part of the recess is to be threaded to screw over the stem of the body. Two slots are to be made in the cap to receive a key, and a hole is to be drilled through the side and tapped to take a brass set-screw. A groove is to be made near the top, which is to be partially closed by spinning over the edge. Four escape holes are to be drilled at an angle from the recess on the under side, into the groove.

=Base Plug.=--The base plug is to be threaded externally to fit the bottom of the body. Two holes are to be drilled in the under side to facilitate assembling, and a central recess formed with a seating to receive a brass washer with a muslin disk. Six holes are to be drilled at an angle from the upper surface into the lower recess, and a hole drilled and tapped in the bottom to take a screw plug. This plug is to be threaded externally to fit into the bottom of the base plug.

=Time Pellet and Detonator.=--The pellet is to consist of two parts, which are to be turned and bored, the parts being screwed together to secure the detonator. A screwdriver slot is to be made in the top surface, and a seating formed on the outer surface for the suspension ring. The detonator is to be turned all over and recessed, four fire holes being drilled through into the recess. The recess is to be coated with non-acid paint and charged with 0.45 grain of the following composition (giving parts by weight):

Glass 50
Fulminate of Mercury 40
Chlorate of Potash 20
Sulphide of Antimony 30
Shellac (dry) 2.8

The ingredients are to be thoroughly pulverized, excepting the fulminate, mixed dry, and then covered with alcohol. The fulminate will then be added and the whole thoroughly mixed. The composition is to be covered with a brass disk secured by shellac. The recess in the plug is to be coated with a composition of shellac and rosaniline and filled with 1¹⁄₂ grain of shrapnel powder compressed with a total pressure of 60 pounds. The detonator is to be inserted in the holder, and secured in place by the screw plug, the two being locked together by a small brass pin.

=Percussion Pellet.=--The percussion pellet is to be machined all over, two holes being bored in the upper surface and a slot cut to receive the firing pin. Two holes are to be drilled at right angles to the slot and parallel to the flat surfaces, one to receive the pivot for the firing pin and the other for the centrifugal bolts. The sleeve is to be machined all over, and is to be a driving fit on the pellet. Two spiral springs and two small pellets, and a pivot pin for the firing pin, are to be provided. All parts, except the pivot pin, are to be tinned all over. The parts are to be assembled, and a hole drilled into the sleeve and pellet, and a small brass pin driven in.

=Percussion Detonator and Holder.=--The percussion detonator is to be turned and recessed on both sides, two flash holes being drilled between the two recesses. The smaller recess is to be charged with 0.45 grain of the following composition (the figures giving parts by weight):

Chlorate of Potash 43.19
Sulphide of Antimony 21.5
Sulphur 7.5
Glass 10.5
Shellac 1.7

The ingredients are to be thoroughly pulverized and mixed dry. Alcohol will be added to dissolve the shellac. The detonator will be formed by pressing the mixture, while in a plastic state, into the recess. On the evaporation of the alcohol the composition should adhere strongly to the metal. A brass disk, 34 in Fig. 5, is to be secured over the composition with shellac. The larger recess is to be varnished with a composition of shellac and rosaniline, and 4 grains of shrapnel powder compressed into it with a pressure of 127 pounds and covered with a disk of tin foil, shellacked on. The holder is to be threaded externally to fit in the body, and recessed to receive the detonator, a central hole and two key-holes being made.

=Pellets.=--The powder pellets are to be made to the shapes shown in Fig. 5. Pellets 33 and 35 are to be made from compressed unglazed black powder, with clearance holes as shown; pellets 32 and 36 are to have the clearance holes filled with 0.05 and 0.02 grains, respectively, of gun cotton.

=Percussion Springs.=--The springs used in the percussion plunger must be made to the form and size shown in Fig. 5, and tinned. The percussion safety pin spring (21) is to be made from 0.012 inch diameter brass wire, tinned, and wound so as to give a free height of 0.150 inch ± 0.030 inch, and at such a spacing as to give 44 coils per inch. The percussion restraining spring (30) is to be made from 0.015 inch diameter brass wire, tinned, and wound so as to give a free height of 0.500 inch ± 0.050 inch, and at such a spacing as to give 36 coils per inch. This spring is to have a maximum resistance of 1.65 and a minimum of 1.5 ounce at an assembled height of 0.370 inch.

=Suspending Ring.=--The suspending ring for time detonator pellet is to be made of brass wire. The ring is to be of such strength that when tested with steel counterparts of the stem and pellet, the latter is forced through the ring with a deadweight load of from 69 to 77 pounds.

=Cloth Washers.=--The cloth washers are to be made from waterproofed felt cloth, with holes cut in them. The body and graduated time train washers 16 and 17, respectively, which are shown in Fig. 5, are to be subjected to a pressure of approximately 10,000 pounds per square inch after assembling, before closing cap is screwed on and adjusted.

=Lacquering and Polishing.=--The exterior surfaces of the fuse are to be polished and lacquered with a lacquer consisting of 1 pound of seedlac, 8 ounces of turmeric, and 8 pounds (1 gallon) of methylated spirits. The groove in the top and bottom composition rings, the magazine recess in the body, the powder channels and groove in the base plug, and the powder chambers of time detonator and percussion detonator holder, are to be lacquered with a lacquer consisting of 10 grains of rosaniline, 1¹⁄₂ pound of powdered shellac, and 1 quart of methylated spirits.

=Screw Threads.=--The screw threads must, unless otherwise stated on the drawing, be of the British standard fine screw thread, and conform to the standard gages of the government inspector. For fuses not made in England, the British standard threads will not be insisted upon, except for the large thread on the body.

=Time Arrangement.=--The grooves on the under side of the composition rings are to be charged with 56 grains of No. 22 meal powder compressed at 68,000 pounds per square inch; the rings are then to be faced off, and the holes at the ends of the channels drilled. The onion skin paper washers are to be secured to the surfaces by shellac. Perforated pellets of black powder are to be inserted in the flash hole in the top ring, escape hole and flash hole in bottom ring, and flash hole in the body, the pellets for escape hole in bottom ring and flash hole having the perforation filled with loose gun cotton. The space at the end of the channel in the bottom ring is to be filled with loose meal powder. An onion skin paper patch is to be secured over the flash hole in top ring, and the escape hole in bottom ring closed by a brass disk secured by two center-punch holes, and coated with shellac. The cloth washers are to be secured on the upper faces of the body and the lower time ring with fish glue, and subjected to a pressure of 10,000 pounds per square inch.

=Assembling and Closing.=--The different parts of the fuse are to be put together as in the assembly view, Fig. 1. The cap is to be screwed down so that a turning moment of 325 ± 25 inch-ounces will just turn the ring, the cap being secured by means of a set-screw. The bench or table upon which the tensioning apparatus is fixed is to be jarred by tapping with a mallet to assist the turning of the ring. The base plug is to be screwed into the body, and the magazine filled with fine-grain powder through the filling hole. The bottom of the fuse is to be coated with shellac varnish.

=Delivery.=--The fuses are to be delivered in lots of 2000, an additional 40 being supplied free, for purposes of proof. In the event of further proof being required, the fuses will be taken from the lot.

=Proof.=--The fuses selected for proof will be tested as follows:

(a) Ten will have the percussion arrangement removed, and will be tested to determine the mean time of burning at rest. The time train will be set at the highest graduation mark. The mean time of burning, set full when corrected for barometer, will be 22.9 seconds ± 0.4 second. The constant to be used, when correcting for barometer, is 0.023 of the mean time of burning, for every inch the barometer reads above or below 30 inches, being plus when above and minus when below. The difference between the shortest and longest time of burning is not to be more than 0.5 second. If the lot fails to pass this test, a further proof will be taken; the fuse must burn within the limits specified above, otherwise the lot will be rejected. Should the detonator fail to ignite the time ring, a second proof will be taken; should a similar failure occur at second proof, or should there be more than one such failure at first proof, the lot will be rejected.

(b) Twenty fuses will be fired, at the same elevation, in any of the following guns, with full charges, and the time of burning noted. The requirements as to the result of the firing with the fuses set at different graduations are as given in detail in the following:

1. The mean difference from the mean time of burning of the 20 fuses is not to exceed:

In 18-pounder guns if set full 0.14 second
if set 16 0.11 second

In 13-pounder guns if set full 0.2 second
if set 14 0.13 second

The difference between the longest and shortest fuse is not to exceed:

if set full 0.75 second
In 18-pounder guns or omitting one fuse 0.6 second
if set 16 0.6 second
or omitting one fuse 0.5 second

if set full 0.9 second
In 13-pounder guns or omitting one fuse 0.7 second
if set 14 0.7 second
or omitting one fuse 0.5 second

2. If there is one blind fuse, a second proof will be taken. If there is a blind at second proof, or more than one such failure at first proof, the lot will be rejected.

(c) Five fuses from a lot will be tested, in shrapnel shells, by firing them set at “0” from a gun with a muzzle velocity of 1500 to 1800 feet per second. The fuses should burst the shells at from 5 to 50 yards from the muzzle of the gun. Should there be a burst in the gun, the lot will be rejected. Should any fuse fail to act within 50 yards, second proof will be taken; should a similar failure occur in the second proof, or should there be more than one such failure at first proof, the lot will be rejected.

(d) Five fuses from a lot will be tested in common shells by firing them over sand, at such an elevation that the angle of descent will not be more than 4 degrees. When one only of a set of fuses so fired fails to burst on first graze the lot will be accepted without further proof; if there be more than one failure to burst on graze in the second proof, the lot will be rejected. The fuses must burst at the point of impact. For percussion proof the time ring is to be set on the bridge.

(e) A premature explosion due to the fuse in any of the foregoing proofs will cause the rejection of the lot.

(f) Should any other gun be introduced for proof of this fuse, which differs from the above guns in either muzzle velocity or twist of rifling at muzzle, the above conditions will be subject to modification.

(g) If, in the proof of any delivery, defects are found involving the serviceability of fuses, additional proof may be taken from any other delivery not finally closed, to ascertain if the defect is general. Should the fuses fail at this further proof, the delivery will be rejected without reference to the original proof. The total proof of any delivery shall not exceed 5 per cent of the lot. The contractor will be required to replace all fuses expended in further proof or examination free of charge, which, whether fired or otherwise tested, will become the property of the government.

=Inspection.=--(a) The components of the fuses, during manufacture and assembling, and the completed fuses after delivery, will be subject to examination and gaging by, and to the final approval of, the chief inspector or an officer deputed by him. Any component or fuse, which is not finished to the satisfaction of the chief inspector, or his representative, or which has any flaw or imperfection, will be rejected.

(b) If, at any time during examination, it is found that defects of any nature which involve rejection of the defective components, or fuses, amount to 5 per cent of the number in the lot, the lot will be rejected.

GRADUATION TABLE FOR TIME RING ON BRITISH COMBINATION TIME AND PERCUSSION FUSE

+--------------+------------+
| | Angle |
| Graduation +------+-----+
| | Deg. | Min.|
+--------------+------+-----+
| 0 to 5 | 26 | 0 |
| 0 to 1 | 16 | 45 |
| 1 to 2 | 15 | 15 |
| 2 to 3 | 15 | 30 |
| 3 to 4 | 16 | 30 |
| 4 to 5 | 14 | 40 |
| 5 to 6 | 14 | 35 |
| 6 to 7 | 14 | 15 |
| 7 to 8 | 13 | 55 |
| 8 to 11 each | 13 | 35 |
| 11 to 12 | 13 | 20 |
| 12 to 13 | 13 | 10 |
| 13 to 14 | 13 | 0 |
| 14 to 15 | 12 | 50 |
| 15 to 16 | 12 | 30 |
| 16 to 17 | 12 | 0 |
| 17 to 18 | 11 | 30 |
| 18 to 19 | 13 | 10 |
| 19 to 20 | 14 | 30 |
| 20 to 21 | 16 | 20 |
| 21 to 21.2 | 3 | 30 |
+--------------+------+-----+

(c) If, at any time during examination of the lot, it is found that 5 per cent of fuses in the lot depart from the approved design, further examination will be suspended. The whole of the lot must be re-examined by the contractor and those fuses which are incorrect to design eliminated. Those fuses in which the departure can be rectified may be changed to the approved design by the contractor. The lot may then be re-submitted for examination.

=Tests for Safety in Transportation.=--From each lot, 20 time and 20 percussion plungers are to be tested to ascertain the correctness of their weights and static resistances. Lots of plungers not correct within the tolerence allowed will be rejected. At the commencement of manufacture, 6 time and 6 percussion plungers from each lot will be subjected to a drop test against a steel block 11.5 inches in diameter, 4.5 inches thick, resting on a concrete pier, to determine the limit in heights at which the same will arm when carried in standard dropping pieces. One of the pieces weighs 15 pounds and has the form of a 3-inch shell; the two other pieces are lighter and smaller. No concussion plunger is to begin to arm when falling in the lighter piece from a height of 4 feet 6 inches; all shall fully arm in the shell with 14 feet 8 inches drop. No percussion plunger is to begin to arm in the special piece falling with 6 feet 2 inches drop; all shall fully arm in the shell with a 17 feet 6 inches drop.

=Jumbling and Jolting Test.=--Ten fuses will be placed, one at a time, in a wooden box approximately 16 inches by 11 inches by 5 inches inside dimensions, revolving at thirty revolutions per minute, about one of its diagonals, for four hours. The fuses will then be placed in an adjustable fuse-holder on the end of a hinged lever 16 inches long, which, by the motion of a cam, is raised 4 inches, thirty-five times per minute, and allowed to drop on an iron anvil. The fuses are thus dropped for an hour, point downward, base downward, and side downward, respectively. The primer shields must not be marked, and the time trains, powder pellets, etc., must be intact.