Designing Settriggers.The three main differences between double settriggers for rifles and pistols
1. Trigger plates are a lot shorter on pistols. This leaves less room to fit parts and the main spring has to be shorter and stiffer.
2.The rear end of the trigger plate has to be inlet below the surface of the pistol stock or it will conflict with the trigger guard tang.
3. Trigger plates curve a lot more on pistols.
Bottom loading verus top loading front triggers.With the top loading trigger, only the trigger shoe has to fit through the slot in the triggerplate. This makes it easy to draw the trigger blade, but limits the trigger shoe to a “straight nail” with the same width as the blade. With a bottom loading trigger, blade has to fit through the slot of plate. This makes the blade harder to design, but gives you more options designing the trigger shoe. Take your pick. I chose bottom loading because I like broad trigger shoes.
Making brass patterns.When designing the triggers, draw the plate so it fits the curve of the grip, then draw in the triggers. Cut the patterns out of brass sheet stock. I used 0, 04” thick brass. Check how the triggers move in relation to each other. The rear tail of the front trigger can be tricky to get the right length. If it is to long the triggers will bind.
If it is too short, you will have problems placing the adjustment screw in the plate.
Pivot point placement.The hook on the front trigger engages the notch on the rear trigger. Draw a vertical line through the hook and place the front trigger pivot point somewhere on this line. If you place it in front of the line, you will get an unstable trigger that can release unexpectedly. If you place it behind the line, you’ll get a heavier trigger pull. Placement of the rear trigger pivot point is not critical.
Making the triggers.I made my triggers by cold forging 1/8” thick mild steel.
Front trigger.I filed the curve of the trigger shoe out of the blank and drew a line 2/8” parallel and below it. Next I peaned the blank down to this line, using a large punch.
Trenching with a punch, followed up with plandishing with a hammer, was the quickest way to move
the metal.
Next I filed the shoe to the finished size and shape, glued the blade pattern to the blank using “scotch weld, stencil glue”. Do not use water based glues. They distort paper patterns. Then I drilled the pivot hole and sawed out the trigger with a jeweler’s saw (blade +6). Lubricate the blade with bee’s wax.
Rear triggerThe rear trigger was made the same way, except that the shoe was forged horizontal and curved hot using a pair of pliers and a propane torch
Making the triggerplate and installing the triggers.The trigger plate is made from 10mmx10mm (0.4”x0.4”) mild steel bar stock.
The trigger plate for pistols has to curve to fit the grip. The best way to get a smooth curve this is to bend the bar stock hot before doing any shaping. If you cut out the “ears” first, there is a tendency to distort the curve here. Likewise bending after cutting the trigger slots can mess up the slot dimensions. Use a bending block. This guaranties that the trigger plate will follow the curve of the pistol grip.
Making the bending block.I drew the curve of the on a steel beam and installed a series of bolts along it. I heated the bar stock to 840C in a heat treating oven and did all the bending in one heat. You could do it with a heavy duty propane torch using several heats. Cutting the blank a couple of inches extra long, makes the bending easier.
If you are not careful it is easy to twist the blank while bending it. You can get rid of the twist by reheating the blank and squeezing it in a vice.
Truing up the blank.No matter how careful you have been, the blank will wobble when laid on a flat surface. The metal on the inside of curve has been compressed and the metal on the outside has been stretched. The bottom flat of the blank is now 10,25mm wide and the top flat 9.85mm wide, where the curve is tightest. The blank is still 10mm x 10mm where it is straight. I use a large metal rasp to true up the sides of the blank and use the straight front end as guide.
Next, I draw file the top and bottom flats to get rid of fire scale and square up the blank.
Then I paint it with machinist blue and trace the pattern of the blank. Before cutting out the profile, I modify it so that the rear of blank is 2/8” thick, not 1/8” . I’ll explain why later. The easiest way to cut out the trigger plate is to drill a series of holes along the profile ant cut through the remaining steel with a jeweler’s saw. If you use a press drill, what’s left of the holes is an excellent guide for filing the plate level. I also drill the holes for the trigger pins at this stage.
Cutting the trigger slots and ruff adjusting the trigger blades.I put extra long pins in the plate and mount the trigger on the side of the plate. By moving the triggers, I can find the placement and length of the slots. Drill a series of holes for the slots from the bottom of the plate. Use these holes as a guide for sawing out the slot between the ears. Next saw out the individual slots for the front and rear triggers. Mount the triggers in the slot and file the blade notches to fit.
Why is the rear end of the plate this fat?The front end is a little over 1/8” thick while the rear end is 2/8”thick. This is to make room for the trigger guard tang. The plate is inlet flush with the wood. Then take it out of the stock and file the rear of the trigger plate so it tapers to 1/16” below the surface of the wood. The rear portion of the plate is now in bottom of the inlet for the trigger guard tang. The tang is inleted on top of the trigger plate. Due to the length of the plate, this is the only way to make room for the tang.
Then I install the triggers and ruff file the length of the hooks so they can move without jamming.
Next I drill and thread the holes for the set screw, backlash screw and mainspring screw.
Backlash and mainspring screws are M4 (4mm) and the set screw M3 (3mm). Several books recommend using interference fit for the set screw. I have tried that, but every time I ended up twisting the screw off. Therefore I threaded the holes completely all the way. Place the set screw as close as possible to the front trigger. If placed in the middle between the two triggers, it won’t reach the “tail “of the front trigger. On bottom loading triggers, the length of the trigger slot severely limits the length of the tail.
Making the springs..The mainspring.The spring is made out of a piece of 0.7% carbon steel, 3mm (1/8”) thick. I anneal the steel by heating it to 840C (1544F) for 45minutes and letting it cool overnight in the oven. Next I cut out blanks 65mm x 8mm (2.5” x 0.3”). Then I file out the spring nose (0.5”x0.1”).
I curve the spring in a vice, hitting it with a hammer. I start at the nose and work my way to the rear end.
I try to get the body of the spring to follow the curve of the trigger plate and the nose to go down into the rear trigger slot. This gives the spring the necessary pretension. Without it, it’s too weak to trip the lock sear.
I use a scribe to mark the trigger plate mainspring hole onto the spring blank and drill the hole. When mounting the spring in the trigger plate, you’ll find it is too long and blocks the rear trigger. The length is easily adjusted by filing the nose shorter.
The weak spring.The weak spring is cut out of 1/16” thick spring steel.
The end of the hook is heated bright cherry red with a torch and bent 90 degrees, so the spring can’t slip off the front trigger.
Do not mount the weak trigger spring on the right side of the trigger plate. The lock sear will interfere with its function.
Hardening and tempering the springsI preheat my heat treating oven to 840C (1544F) soak the main spring for 20 minutes and quench in oil. Soak the weak spring for 5 minutes. For tempering I preheat the oven to 400C (752F) and soak both springs for 30 minutes, then air cool at room temperature.
Best regards
Rolf
