APPENDIX VI. TEST OF BASE PERCUSSION FUSE FOR FIELD, SIEGE, AND SEACOAST THE ORDNANCE BOARD, U. S. A., New York City, January 9, 1902. SIR: The board respectfully submits herewith a report of trials made with various types of Frankford Arsenal base-percussion fuses since May, 1900, to include the matter contained in several communi cations upon the same subject, namely: May 28, 1900 (23100), December 20, 1900 (35650), January 5, 1901 (35650-Enc. 6), June 27, 1901 (35650-Enc. 11), and September 14, 1901 (35650-Enc. 15), and the firing records pertaining thereto are incorporated herewith. The object at first sought was an improvement in the service patterns of ring-resistance fuses to include a type that would function with side impact of the projectile on water as well as on land. In the course of the trials, however, several types of centrifugal fuses were presented, and as these promised greater safety in service than the existing patterns their trials have been extended to develop a type which is now proposed to replace the ring-resistance type in service. Two designs of centrifugal fuses have been extensively tested. The one preferred is designated the revolving pin fuse from a distinctive feature of the firing pin, which lies flat in the plunger under ordinary conditions, but is revolved into the armed position by the centrifugal force due to the rotation of the projectile when fired from a rifled cannon. The trials, in chronological order, have included the following fuses: F. A. EXPERIMENTAL SIDE-IMPACT, BASE-PERCUSSION FUSE. (Plate I.) The fuse, as designed by Capt. B. W. Dunn, is shown on the copy of the original Frankford Arsenal drawing, dated October 17, 1899, berewith. This represents the large fuse W. The smaller fuses, A and C, are of similar design. The novel features of this fuse are in the plunger, which is supported by a conical pin at the rear and a conical ring fitting over a corresponding slope at the front, so arranged that the plunger will be forced forward on impact, even though the projectile strikes on its side or within limits, when the base is inclined downward. The resistance of the fuse to arming is controlled by a spring ring on the spindle similar in design to the service fuse. The several lots of this design of fuse received at the proving ground were tested, as follows: Lot 1. Six side-impact W, for 12-inch B. L. mortar shell. These fuses differ from the drawing, Plate I, only in having the extra primer shield removed, drop tests at Frankford Arsenal having shown that the extra shield induced irregular action. Five were tested. Lot 2. Twenty-five side-impact A, for 5 and 7 inch siege shell and 12-inch mortar shell tapped for A fuse. Sixteen were tested. Lot 3. Fifty side-impact C (25 each, low and high) for field cannon. Nineteen were tested. Lot 4. Fuse C of service pattern with primer shield 0.0015 inch thick, to test action at graze on land and water. Ten were tested. Lot 5. Five side-impact W special, with side retention pin in plunger, and fulminate primer. All were tested. The following conclusions are drawn from these trials: 1. Side-impact fuse W gave good action in 12-inch mortar shell at 60° elevation with low charges, causing side impact of the projectile on water. 2. Side-impact fuse A gave unsatisfactory action in 12-inch mortar shell under the same conditions; this is attributed to the relatively light weight of plunger in fuse A. This side-impact fuse gave good action in 7-inch mortar shell at 65° to 70° elevation with low charges, causing side impact of the projectile on land; but gave premature action in 5-inch siege gun with full charges. 3. Side-impact fuse C (low) gave good action in 3.6-inch mortar shell at 60° elevation with the minimum service charge on land, and the fuses of both low and high resistance acted well in 3.2-inch field shell, at zero elevation with full charges, for graze on land and water. 4. The premature action of the side impact A in 5-inch siege gun and of W in 3.2-inch field gun, although the latter is not a service condition, point to the principal defect of the design, viz: The centrifugal action due to the rotation of the shell when fired may throw the plunger out of center, and when this occurs the plunger will be forced forward prematurely by the guiding surfaces, which are intended to move it forward on side impact only. The development of this defect led to a suspension of the trials of this design of side-impact fuse. 5. In the comparative trials the A and C patterns of the service fuse (ring-resistance type) gave about equally satisfactory action with the side-impact fuses under the most trying conditions, namely: 3.6-inch mortar at high angle and minimum service charge; 7-inch mortar at high angle and reduced charges, and 3.2-inch field and 5-inch siege guns, at 0° elevation, with the projectiles striking by graze on land and water. The important conclusion drawn from this is that the side-impact feature is not a necessary adjunct of field and siege fuses, except possibly for the 7-inch mortar. At the shorter ranges which are included for the service of this mortar, as now mounted, the tendency of the projectile to fall in different positions is such that a side-impact feature is desirable in its fuse. F. A. EXPERIMENTAL CENTRIFUGAL, BASE-PERCUSSION FUSE, M'BRIDE DESIGN. (Plate II.) The designs include a centrifugal fuse simply and a centrifugal fuse for side impact, of the several sizes required in service. The centrifugal feature was designed by Matthew McBride, foreman, Frankford Arsenal. The accompanying drawing, Frankford Arsenal, March 16, 1901, revised to August 15, 1901 (Plate II), shows the construction of the centrifugal, side-impact W fuse, and suffices to explain the construction of the remainder. The only difference between the simple centrifugal fuse and the centrifugal side-impact fuse is that the plunger in the latter is tapered to the rear and terminates in a conical projection fitting into a conical recess in the base of the fuse cavity. In the simple centrifugal fuse the plunger is cylindrical, with flat base, and conforms in diameter to the fuse cavity. The distinctive feature of the design consists in supplying the fuse plunger with three shields fitting in longitudinal slots in the plunger 60° apart, hinged near the bottom by means of a pin journaled in the fuse body and provided at the top with flat projections which, in the unarmed position of the fuse, serve to interpose solid metal between the upper face of the plunger and the rear face of a projection of the fuse cap, thus keeping the firing pin at a safe distance from the primer. The spiral springs (0), acting in a direction perpendicular to the axis of the fuse, are depended upon to keep the shields in their unarmed position. The effect of centrifugal force is to move them out, compressing the springs. When out, any retardation of the projectile moves the plunger forward, the shields encircling the projection from the fuse cap and the firing pin entering the primer recess. The spiral spring (j) serves to keep the plunger to the rear during the flight of the projectile. Plungers of this design can be used in the service fuse bodies, but they require special caps. The firing pin () is a separate piece forced into its cavity and held there by a pin through the plunger. (Not shown in the drawing.) The three shields are supplied to increase the safety features of the fuse, any one of them in its unarmed position being sufficient to prevent premature action. Supposing these shields to remain in their safe position, the resistance to forward motion of the plunger, in case the fuse or projectile is dropped on its point, depends upon the resistance of the walls of the hollow projection from the rear of the fuse cap and upon the area of contact of the rear surface of this cap with the inner edges of the three shields. It is necessary to arrange this area so that with the limited outward motion of the shields there will be secured several hundredths of an inch clearance between the inner edges of the shields and the outer diameter of the fuse-cap projection, in order to allow the plunger to move forward. This condition makes it more difficult to construct, on this design, small fuses than large ones; on the other hand, the small fuses, being used in the high-power guns, can be given a higher resistance to arming, which increases their safety. A fuse of this design of the "A" size has been dropped directly on its point from a height of 30 feet without firing the primer, although the surface of contact between the fuse cap projection and the three shields showed considerable deformation. There is no unity of action of the three shields of this design, as there is in the two parts of the plunger of the revolving pin design. A side blow will cause the downward shield to be thrown outward to its armed position, but at the same time the others would be forced more securely into their unarmed position. Such a blow delivered to the revolving pin plunger would necessarily tend to close the two halves. In the same way, continued jolting of the McBride fuse on its point would deform the bearing surfaces and tend to make them conical rather than perpendicular to the axis of the fuse. In course of time this would introduce a wedgelike action, tending to open all of the shields. The different lots of these fuses received at the proving ground were tested, as follows: Lot 1. Twenty-five centrifugal C (tested under direction of the commanding officer of the proving ground). Lot 2. Twenty-five centrifugal A (tested un er direction of the commanding officer of the proving ground). Sample centrifugal, side-impact fuse W; firing record February 20, 1901, 3.2-inch gun. Lot 3. Twenty centrifugal, W, arming at 900 revolutions per minute. After 5 of these were tested in 3.2-inch field gun (February 8, 1901), with one failure and one explosion on second ricochet, the remainder were returned to the arsenal to increase the clearance of the shields; 13 in all have been tested. Lot 4. Twenty centrifugal, side impact W, arming at 900 revolutions per minute. On arrival of these fuses at the proving ground 4 were found to have been ignited in the packing box in transport. The lot was returned to the arsenal and altered by reducing the primer orifice and giving better support to the spiral spring in front of the plunger; 15 have been tested. Lot 5. Ten centrifugal, side impact A, arming at 900 revolutions per minute. One of these fuses was ignited in the packing box in transport from Frankford Arsenal to the proving ground; 2 have been tested. The following lots received have not been subjected to firing tests: December 5, 1901, 25 centrifugal C, arming at 3,000 revolutions per minute. 1. The simple centrifugal fuses, sizes C and A, gave very satisfactory results. There were no prematures in the 50 fuses fired. There were in all 5 failures to function properly, namely: 1 out of 14 against light wood screens, and 4 out of 11 fired at zero elevation from guns to burst at graze on land or water. Ten fired from guns at 2° elevation, 5 from 3.6-inch mortar, 7 from 7-inch mortar, and 3 from 12-inch mortar, all on land at 45° elevation, functioned properly. 2. The simple centrifugal fuse W gave no prematures, but the 3 fired in 12-inch mortar shell failed to explode on water, thus indicating the necessity for a sideimpact arrangement in fuses intended for this service. 3. The centrifugal, side-impact fuses, sizes W and A, functioned without failure in 17 fired, except 1 doubtful explosion in 12-inch mortar shell on water. 4. However, the explosion of 4 W and 1 A centrifugal side-impact fuses in the packing boxes during transportation from Frankford Arsenal to Sandy Hook constitutes a grave defect, and indicates at least that this design is not applicable to patterns of such low arming resistance as 900 revolutions per minute. The spiral springs which restrain the outward movement of the shields in this case are too light to be fully reliable. All the tests, including shop tests at the arsenal, show that with a resistance to arming not below 1,500 revolutions per minute this fuse should be safer than the present service (ring-resistance) type, and it might be used where the higher arming limits are permissible. But in view of the limited area of resisting metal to conserve safety, previously referred to in the description of the design, the board concluded to suspend the tests of this fuse and prosecute fully those of the second design of revolving pin fuse. F. A. EXPERIMENTAL REVOLVING PIN, BASE PERCUSSION FUSE—FIRST (Plate III.) The design is due to Capt. B. W. Dunn, Ordnance Department, U. S. Army. The first pattern of the fuse presented for trial is shown on the accompanying drawing, Frankford Arsenal, August 23, 1901 (Plate III). The firing pin in its normal position is revolved so as to point away from the primer. It is assembled on a shaft, which is connected with two centrifugal nuts. The seat for the shaft being partly in the nut and partly in the fuse plunger, it is seen that the shaft acts as a key 7 for the nuts, to prevent their rotation as they move outward under centrifugal force. The hole in the nut forming the seat for the shaft contains square spiral grooves with a pitch of two per inch, and pins located in the shaft fit into these grooves. The spirals are right-hand in one nut and left-hand in the other. When the nuts fly out under centrifugal force the shaft is caused to revolve, this motion being limited to bringing the firing pin to a vertical position when the nuts have reached the limit of their outward motion. This motion can be produced by inserting the end of some sharp instrument under the firing pin and revolving it up to its upright position. The three parts, the shaft and two nuts, constitute what may be termed the "arming unit," and a very essential feature of the fuse is that this unit shall have a free motion from one side of the plunger to the other. The result of this is that it is impossible by any jarring or jolting to produce any tendency of the fuse to arm. If the shaft and pin were fixed in a central position, jolting would tend to produce a motion of the nut along the shaft, which would have to be resisted by a spring or the friction of the key pin in the spiral groove. This is all avoided by the unit motion referred to. It will also be noticed that a simultaneous tendency of the two nuts to fly outward is necessary to arm the fuse, and this can be produced by rapid rotation alone. The small spiral spring in the center of the two nuts tends to keep the fuse in an unarmed position. The fuse is safe against premature arming without this spring, and in that respect it is thought to be unique and to possess an advantage never before presented in a centrifugal fuse. The natural tendency of the pin, as the result of the force of gravity, is to stay in its unarmed position, and it requires, without the spring, by actual measurement, about 700 revolutions per minute to arm it. Jumbling tests have shown that without any spring it is impossible by any jolting or jarring to arm the fuse. The two spring pins in the fuse cap are introduced for the purpose of keeping the plunger during flight of shell in its rear position, in order that all eccentric rotation of plunger may be prevented and that the full force of the wedge in the rear may be secured in case of side impact. They also insure that the space between the plunger and the cap shall be such that the firing pin will meet with no resistance from the cap when it revolves to its armed position. Thirty fuses of this design, size W, were received for test. They comprised 10 with the pin shaft in the upper side of the nuts, as shown on Plate III, and 20 with this shaft in the center of the nuts. After 9 had been tested in a 3.2-inch field gun (June 25, 1901), with failure to function when fired to burst with low angle of impact on water, the remainder were returned to the arsenal and altered by lengthening the firing pin and by placing stops to limit the outward motion of the nuts. Twenty-seven in all have been tested. The test of these fuses after the alteration was satisfactory, except in the 7-inch mortar shell fired with low charges on water. As, however, a simplification and improvement of the design was then brought out by Captain Dunn, the trials of this pattern were suspended. |