MARK 6 MOD. 2 - INFORMATION AND INSTRUCTIONS

ILLUSTRATIONS:

16-1 to 6

- BuOrd Sk. No. 109322 - 68w-1 to 3

1. Pistol Mk 6 Mod 2, Figure 1, is a modification of the basic hydrostatically operated Mk 6 type. It has a depth setting range of 30 to 1000 feet. It is issued for use, with Booster Extender Mechanism Mk 6 Mod 2, in Depth Charge Cases Mk 9 Mods 2 and 3. Standard detonator and booster components, previously described, may be used interchangeably with the Pistol and Booster Extender Mechanism Mk 6 Mod 2 to make up a depth charge assembly.

2. The Depth Setting Range of the pistol is carried on two dials. The outer dial, stam-ped on the pistol flange, provides for index pointer settings of 30, 50, 75, 100,150,200, 250, 300 and "Safe." The inner dial plate, attached to the deep firing mechanism, provi-des positions for valve settings from 350 to 1000 feet, in 50-foot intervals, and the de-signation "0-300." The depth setting feature of this pistol is similar to the Pistol Mk 6 Mod 1.

3. Pistol firing at shallow depth settings (30, 50, and 75 feet) is a function of the time required for water to enter the pistol hydrostatic chamber through the passages of the deep firing mechanism even though the pistol is operated by hydrostatic pressure. In this respect the deep firing mechanism valve of the Pistol Mk 6 Mod 2 is designed to accom-plish more rapid filling of the pistol chamber than is obtained in the Pistol Mk 6 Mod 1. Consequently the firing of Pistol Mk 6 Mod 2 will conform more closely to the shallow depth settings noted. Data on depth settings vs. firing time are noted in paragraph (7).

4. The Safe Setting feature of the Pistol Mk 6 Mod 2 may be relied upon to prevent fi-ring of the pistol due to accidental operation of the parts normally functioned by hydro-static pressure. Firing of Pistols Mk 6 and Mk 6 Mod 1, when set on "Safe" and attached to depth charges which were accidentally subjected to hydrostatic pressure by sinking of the ship carrying them, has been reported. Both laboratory and sea tests conducted during the development of the Pistol Mk 6 Mod 2 disclosed that pressure equivalent to depths of 1000 to 1500 feet would, in some instances, produce distortion of the spring engaging collar and elongation of the piston stem, of Pistols Mk 6 and Mk 6 Mod 1, suffi-cient to fire the pistol when the index pointer was set on "Safe." This defect has been overcome in the Pistol Mk 6 Mod 2 by the installation of critical parts of suitable strength.

5. In this connection, the Safety System of a depth charge fitted with Pistol and Booster Extender Mechanism Mk 6 Mod 2 is based upon the ruggedness of the pistol parts to prevent firing of the detonator at a pressure which is greater than the pressure required to rupture either the pistol bellows or the booster extender bellows. A 3/8-inch hole in the pistol mechanism casing provides a vent into the depth charge case central tube for the surge of water pressure through the ruptured pistol bellows, and thereby prevents this surge from acting on the release plunger to cause firing of the detonator. When the central tube of the depth charge case is flooded by either pistol bellows or booster extender mechanism bellows rupture, the pressure differential required to operate the pistol is removed and the depth charge becomes a dud.

6. New and redesigned appendages as follows are attached to the Pistol Mk 6 Mod 2:

(a) Safe setting lock (spring type) noted in NAVORD OTI M12-43 is furnished with each pistol. This device, with depth setting wrench safety stop and knobbed cover, is secured to the pistol guide tube with twine. When the pistol is assembled in the depth charge case, the safe setting lock and wrench stop should be attached as noted on the instruc-tion tags wired to these parts. If the spring type safe setting lock is lost or damaged, holes in the index pointer lug are provided for use of the wire type safe setting lock no-ted in this pamphlet.

(b) Knobbed safety cover is provided with a more rigid top to insure a complete fractu-re of the soldered joint when the knob contacts the stripper plate on the after end of the release track. It is important that the knob be completely wiped from the cover so that a full and unobstructed opening in the cover will be available for the passage of wa-ter into the pistol. Both knobbed and plain covers having additional improvements for ease in attaching and removal will be secured to pistols delivered by the contractor be-ginning about 1 October 1944. The instructions noted in this pamphlet relative to the use, of safety covers should be carried out.

(c) Detonator holder locking spring has been improved to prevent distortion when withdrawn and replaced before and after the operation of attaching the detonator. The part is shaped to facilitate convenient manipulation by hand or with pliers. The locking spring must be properly attached after the detonator is secured in place as noted in chapter IV of this pamphlet.

7. Depth setting vs. firing time as noted below may be expected when the pistol is in-stalled in the depth charge cases mentioned. Time is measured from the moment the depth charge strikes the water until it explodes. Variation in time is to be expected due to manufacturing tolerances and other causes. As much care as time and circumstances permit should be exercised in making depth settings on the small dial of the deep firing mechanism.

DEPTH CHARGE CASE MARK 9 MODS. 2 and 3

Pistol

Average Time (Sec.)
From

Depth
Setting

Firing
Depth (Ft.)

Track

Projector

30

60

3.5

3.0

50

70

3.9

3.4

75

85

4.7

4.2

100

5.3

4.8

150

7.5

7.0

200

9.7

9.2

300

14.1

13.6

400

18.5

18.0

500

22.9

22.4

600

27.3

26.8

700

31.7

31.2

800

36.1

35.6

900

40.5

40.0

1000

44.9

44.4

8. Preparation of pistol for installation in depth charge case should, in general, be in accordance with the instructions noted in this pamphlet. However, appropriate supple-mentary instructions as follows should be carried out by authorized personnel in connec-tion with this operation:

(a) Pistols Mk 6 Mod 2 are shipped in substantial wooden boxes, ten pistols to a box. Each pistol is packed in a separate corrugated paper carton. Pistols should be received in the cocked condition, with the plain type inlet valve cover in place, with the index poin-ter set on "30," and with the depth setting mechanism for deep firing set at "500." One knobbed type inlet valve cover, one wrench stop, and one safe setting lock for each pis-tol should be attached to the pistol guide tube with twine.

(b) Depress the valve of the deep firing mechanism with tool provided, as noted in NAV-ORD OCL M1-44. If this tool is not available, one of similar material and size should be made. Care should be taken to see that the tool does not slip off the ball and become jammed between the ball and the valve seat. This circumstance may nick the valve seat and cause the valve to leak.

(c) Set the index pointer on "Safe" with the depth setting wrench. Care must be taken to insure that the index pointer plunger is registered with the depression in the dial plate which coincides with the safe position. This can be determined by noting the motion of the stem of the plunger which projects through the top of the index pointer lug. An audi-ble click may also be noted when the plunger drops into the dial plate depression.

(d) Place the pistol on the deck or on a convenient locker top with the detonator end up. With the thumb and forefinger, or with pliers, withdraw the end of the detonator hol-der locking spring from the hole in the guide tube. Rotate the spring sufficiently to permit the point to rest on the surface of the guide tube. Remove detonator holder and attach detonator.

(e) If a pistol not in the cocked condition is received aboard ship, set the index pointer on "Safe," depress the valve of the deep firing mechanism, and cock the pistol with a suitable piece of rod or a screwdriver. Repeat the cocking operation several times to make sure that the firing plunger release balls are firmly seated on the beveled edge of the guide tube bushing. An improperly cocked pistol may fire accidentally and cause in-jury to personnel attaching the detonator, or it may cause the depth charge to be a dud. Then rotate the index pointer counterclockwise from "Safe" to "30" with the depth setting wrench. An improperly assembled depth setting sleeve or a sheared index pointer stop pin can thus be discovered (by firing of the pistol when the index pointer passes the 50 mark) before the detonator is attached to the pistol and before the pistol is installed in the depth charge.

9. Installation of pistol in depth charge case should in general, be in accordance with instructions noted in this pamphlet. Appropriate supplementary instructions as follows apply to Pistol Mk 6 Mod 2:

(a) Locate the safe setting lock with the attaching cap screw and washer in the pistol carrying flange hole adjacent to the "30" dial mark.

(b) Check the operation of the safe setting lock. (See NAVORD OTI M12-43.) The lock will dig into the lug on the index pointer and become jammed if the pointer is not properly aligned at "Safe" so that the index pointer plunger registers with the depression in the dial plate at this setting. It may sometimes be necessary to loosen the safe setting lock attaching cap screw for readjustment of the position of the lock pivot bushing to obtain satisfactory operation. The cap screw should be re-tightened when the lock functions as intended.

10. Pistol depth settings should be made as noted in chapter IV of this pamphlet for Pistol Mk 6 Mod 1.

11. Pistol upkeep routine for ships should be carried out as follows:

(a) Daily routine as noted on page 77 of this pamphlet, with appropriate changes to suit Pistol Mk 6 Mod 2.

(b) Weekly routine as noted on page 79 of this pamphlet with appropriate changes to suit the Pistol Mk 6 Mod 2, particularly with respect to attachment of safe setting lock.