Select Fire Trigger Mechanism





Select Fire Mechanism Pic


ical since their purpose is to hold the telescoping stock in place. If no tubing is available, a three-eighths inch hole may be drilled lengthwise through either round or square stock to obtain the two needed pieces. The wall thickness should be at least three-thirtyseconds inch, since these will take a considerable beating when the stock is in the extended position.

When the two sections of tubing, which we will refer to as stock retainers, are completed, the trigger housing should be clamped in its finished position against the receiver. Then place the stock retainers in position, the rear end flush with the back end of the trigger housing and the upper side nestled against the receiver. When located in this position, they may be tack welded, with the trigger housing separated from the receiver. Weld the two retainers securely in place, but only to the trigger housing.

A hole, one-half inch in diameter, must be located two and three-fourths (2.750) inches from the outside rear of the trigger housing and one-half inch from the top edge. These measurements are for the center of the hole, naturally. Carefully drill this hole completely through both sides, making sure that it is square with the housing, since the fire selector mechanism will be located at this point.

The trigger should be made from three-eighths inch flat stock of high quality steel, capable of being hardened. It may be formed by drilling interconnecting holes around the outline and filing to shape as previously described, or it may be sawed and bent to shape from a piece three-fourths inch wide by three-eighths inch thick by four inches long. Drill a .191 inch hole with a Number 11 drill for a pivot pin at the point shown in the drawing. Following that, drill a one-fourth inch hole approximately one-fourth inch deep in the bottom side about half way between the pivot pin hole and the trigger nose. The upper portion of a trigger spring will be located in this hole.

The trigger nose should be shaped as shown in the drawing. Since this is the part of the trigger that engages the sear with a close, precise fit, it should only be rough shaped at this time. It should not be finished until the sear is completed.

The fire selector (that is, the switch to select either full automatic, in which the gun will continue to fire as long as the trigger is held down, or semi-automatic in which case a single round will be fired with each pull of the trigger) as well as the trigger pivot pin should be made from round stock as indicated in the drawing. Turn both sides to size and shape them into one piece.

The rear end o. ,he sea,. Note .he showers a, «he extreme right. TheSe shoulders w,H mate to the trigger

The rear end o. ,he sea,. Note .he showers a, «he extreme right. TheSe shoulders w,H mate to the trigger

.191" #11 DRILL

.191" #11 DRILL





Matthew Fitchett

drill with #11 thill.

Matthew Fitchett


Matthew Fitchett

10 X 32 SCREW, 7/8M LONG

Matthew Fitchett

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Matthew Fitchett

After drilling an 11/64 inch hole, spaced one-sixteenth inch from the center, completely through, cut the piece apart and face off each section to the proper width. Enlarge the hole in the right hand section to .191 inch with the Number 11 drill and counterbore it to take a screw head. Tap the left hand section with a ten inch by thirty-two tap to receive a threaded screw which will hold both sections together and serve as a pivot pin for the trigger. This assembly can be said to fit properly when the left and right sides are fitted into the housing, the retaining flanges pulled snug against the housing with the screw tight, and with the trigger on the screw between them working freely, but without side play.

A stop pin must be located in the left side to limit the rotation of this fire selector to 180 degrees. When in full automatic position, the trigger pivot pin will be toward the rear of the gun (in a three o'clock position when viewed from the left side) and directly opposite (180 degrees to a nine o'clock position) for semi-automatic fire. Rotating the fire selector switch 180 degrees should move the nose of the trigger forward or backward one-eighth inch.

The bottom of Ihe tear. The relieved portion in Iront ot the thouldert will allow the trigger to disconnect in semi-automatic fire.

Trigger Springs For Ranger Shotguns

The sear return spring rests in the hole at the Ironl end 0« the sear. The oblong slot in the side permits lore and alt movement. required lor the disconnector to work.

The sear proper should be made from five-eighths inch material. A piece one inch wide and three inches long is required and should be of quality tool steel. It should be sawed, ground, and filed to the shape shown. The portion which projects into the receiver and engages thé bolt should be narrowed to slightly under three-eighths inch. It will have less drag, resulting in an easier trigger pull, if it is narrowed to one-fourth inch. However, it would also have less strength, so I suggest you leave it at three-eighths inch.

Establish a center two and one-fourth (2.250) inches from the rear and one-fourth inch from the bottom of this sear and drill a one-fourth inch hole through for a retaining and pivot pin. Place a close fitting steel plug in this hole and drill another hole one-eighth inch forward of the center of the first hole (centered on the seam between the plug and rim of the first hole). If this is properly done, the remainder of the plug will form a radiused slot when removed. This will allow the sear to slide forward and backward one-eighth inch over a one-fourth inch pivot pin. If the sear will not slide back and forth freely, file and polish it until it does.

Drill another one-fourth inch hole from the front end, centering it between the sides, one-fourth inch from the bottom. This one should be close to one-fourth inch deep. Construct a coil spring and follower as shown, and insert them in the hole. After the pivot pin is installed, the spring should have enough compression to hold the sear firmly to the rear. Then, when the fire selector is set on semi-automatic, the trigger nose will be in the forward position. With the breech block in the cocked position, its spring tension holds the sear forward, causing the trigger nose to bear against the sear. Then, when the trigger is pulled, the breech block moves forward, relieving the pressure on the sear. With this pressure relieved, the compressed spring within the breech block moves it to the rear one-eighth inch, disengaging it from the trigger before it will again engage the sear.

Conversely, when in full automatic mode, the trigger nose is moved to the rear one-eighth inch, and remains in this position, in constant engagement with the sear, thus permitting the breech block to continue to move forward without interruption until the trigger is released.

This probably sounds somewhat complicated; but after you study and understand it, you'll find that it's one of the simplest selective fire trigger mechanisms found anywhere.

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Cutterhead Rifling
broch bloc à. reahtard (cocitidj p oh ward pr8ssurb causfcs skar to m** for*ard, lngauino trlüusk with slàr.

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te1cu» is mwed rearward l/f»" by rutatlum OF fire sslktur switch. is how i* cüktlhlk/ds ehiagb-.ekt with sear.

Trigger Mechanism Submachine Guns

hrekh bluck pohwakd (fired puö1ti0nj trigger and sear in full automatic position.

breech block

The slot at the back of the sear should be roughed in. leaving the shoulders (that contact the trigger nose) longer than necessary. After the hole for the one-fourth inch pivot pin is located, drilled, and tapped, these shoulders and the trigger nose should be adjusted by filing, stoning, and polishing. When the fire selector is turned to semi-automatic, and the trigger is in the forward position, the spring inside the sear should push it to the rear, thereby disengaging it. When the sear is then pushed forward, as it would be with the breech block pressure against it, the trigger,nose should firmly engage the sear shoulders with one-sixteenth inch to three-thirtyseconds inch bearing surface.

One more one-fourth inch hole must be drilled as close to the front of the sear as possible to receive a sear opening. This is simply another small coil spring with enough compression to hold and return the sear to its engaging position.

The forward end of the housing shouid be shaped as shown to enter its receptacle in the rear of the magazine housing. Then drill a three-eighths inch hole through the bottom center of the trigger housing, one and one-eighth (1.125) inch from the outside rear to the center of the hole. With the trigger housing clamped in place on the receiver, locate and drill a corresponding hole in the receiver. A three-eighths inch by twenty-four steel nut may be welded over the hole to receive the stock bolt, which will eventually hold the completed assemblies together.

Left side of complete gun is pictured at right. The tire selector switch on this gun is ditferent trom the one shown in the drawings and described in the text. The one mentioned in the text is much more reliable than the on»? on this gun.

Ruger Mark Schematics

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