25. PULL FIRING DEVICE M1.

a. Description. The Pull Firing Device M1 (produced from Corps of Engineers) is a nonelectric mechanism, designed primarily for use with a trip wire, for firing mines or other explosive charges. A direct pull of from 3 to 5 pounds applied to the trip wire re-leases the firing pin, which is driven by the compression spring into a percussion cap fit-ted in the base. This percussion cap fires a nonelectric blasting cap, attached to the base, which in turn detonates the explosive charge. The device (figs. 18 and 20) mea-sures approximately 4¾ inches long by 5/8 inch diameter. It consists of a head, a hous-ing tube, and a base. The head consists a release pin, a safety pin, and a loading spring. The housing tube contains the firing pin, the firing pin compression spring, and a second safety pin which passes through the body between the firing pin and the percussion cap. The base contains a recess into which a percussion cap is placed, and a projection to which a nonelectric blasting cap is crimped when the firing device is loaded. The firing mechanism consists of a firing pin, a compression spring, a release pin assembly, and a loading spring. The split head of the firing pin is forced against pressure of the compres-sion spring through a small opening or well, in the housing. The release pin enters into and expands the split head of the firing pin spindle against the sides of the well, thus preventing its return,, although the striker is under pressure from the compression spring. The release pin is held in position by the loading spring. Holes in the main head and in the release pin allow insertion of safety pins, thus preventing accidental movement of the release pin to fire the  cap. A soldered joint is made between the main head and the housing tube, so that this part of the device cannot be taken apart. A short piece of flexible wire terminating in a loop is attached to the housing tube at this joint. This is to be used as an anchorage for the firing device. The ring on the release pin facilitates fastening the trip wire to the device. The safety pin through the body positively restrains the firing pin from striking the percussion cap.

Figure 20 - Pull Firing Device M1

b. Functioning. When the safety pins are removed, a pull of from 3 to 5 pounds app-lied through a distance of about 1/32 inch is sufficient to overcome the resistance of the loading spring and cause the tapered end of the release pin to be withdrawn from within the split head of the firing pin. The split head of the spindle, being no longer forced against the well, slips through under the influence of the compression spring. This for-ward movement of the firing pin continues until it strikes the head of the percussion cap contained in the base of the device. The percussion cap is thus fired, and detonates a nonelectric cap crimped to the base.

c. Installation. This device is installed in a manner similar to the combination firing device (par. 24) except that the safety pin through the body is removed last, after all other preparations have been made and tested.

d. Packing. Pull firing devices are packed in boxes, each box containing five devices complete with percussion caps and two 80-foot spools of light trip wire. The boxes mea-sures 4¾ by 4 7/8 by 1 5/8 inches. Each full box weighs 1 pound 3 ounces.