Trigger Assembly

The trigger assembly consists of a housing, trigger, hammer, sear, disconnector and safety, plus a hammer spring and guide, trigger and sear springs, plus appropriate pivot pins or screws.

The trigger housing is made from rectangular bar stock 5/s" wide, 6" long and 1 '/a" deep. Since little or no stress or shock is imposed on this part, it can be made from whatever steel is available. I prefer better material than cold rolled even for parts such as this, simply because it machines cleaner. I used, and will continue to use, 4140 for this part.

The inside is cut out using a W end mill leaving a wall thickness including both sides, one end, and the bottom of .100" to .120". The other end which will be the forward, or front, end is cut out entirely. By using the measurements shown or tracing an overlay from the plan sheet, the holes can be properly located and drilled. As usual these holes should be started with a center drill, then drilled with an undersized drill and finished with the proper diameter drill. Since the holes for both the trigger and sear axis pins are threaded 8 x 40 or 8 x 32 to accept axis pins which screw in place, the holes should be a finished diameter of .136" on the threaded side. A number 29 drill is correct for this. The opposite side is larger at. 164" -. 166" to accept the pin body. Use a number 19 drill for this. The hammer axis pin uses a threaded hole x 24" on both sides. These are drilled with a "Q" drill of .332" diameter. The pin at the upper front edge is M" in diameter with one side tapped for a Yi" X 28 thread. Use a Vt" and a number 3 drill (.213) respectively. This pin is used only to wedge the forward end of the trigger housing in place.

A slot W' wide and W long is cut in the bottom for the trigger to fit through and the trigger guard bent to shape from .100"- .125" sheet metal wide. A ¥»" wide slot is cut in the trigger housing just forward of the trigger opening and a

Homemade Trigger AssemblyHomemade Shotgun Assembly Part

Top view of trigger assembly, showing hammer in cocked position.

matching slot in the forward end of the trigger guard. Taking care to keep this slot lined up the guard is attached to the housing by welding or silver solder. The safety lever works laterally in this slot

AM" hole is drilled through the bottom rear of the housing for a retaining bolt Vt" x 28" x 5" which is purchased commercially. Wait until the grip is installed in its proper position to drill this hole, which is marked through the hole in the grip assuring matching.

The trigger safety, and hammer are cut to shape from '/»" high carbon steel such as 4340. A section of automobile leaf spring works well here. The sear should be made from 5/16" material of the same quality, note that spacers are fitted to both the trigger and sear to keep them centered between the walls of the housing. The hammer is centered by using the %" by 24 T.P.I, hammer screw with a small %" pin extending through the

Homemade Trigger Assembly

hammer and into the bushing threaded into the housing from the opposite side.

The combination trigger bar and disconnector is also made from Vt" material with the forward portion thinned to clear the hammer and hammer spring. The upper "humps" on the disconnector portion should be left oversize to permit fitting after the rest of the gun is assembled.

Three small coil springs are required as shown for the trigger, sear and disconnector. No specific size is required here so long as they are strong enough to return these parts to their pre-fired position and hold them there. Drill "pockets" as shown for the springs to fit in.

The same applies to the hammer spring. The size can vary as long as it is strong enough to throw the hammer forward with sufficient force to fire the shell consistently. The spring guide is made to match.

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  • David Kohl
    What is the trigger guard material on the 201516 Browning BT99 ?
    4 years ago

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