SEAR SPRING PREP — The adjustments that I make to the sear spring are the primary variables that I use to set final trigger pull weight. The lighter I set the sear spring, the lighter the final pull weight and vice versa. Use caution in trying to go lighter than the spring forces listed here. Uncontrolled fire is possible if you do not pay heed.
If you do not have a thorough understanding the operation of the fire control system on the 1911 pistol, you are recommended to have a trained gunsmith adjust your trigger pull.
The 1911 sear spring is a flat leaf spring having three legs, that works as a return spring for the sear, disconnect and grip safety. When viewed from the rear, the leaf on the left works the sear, the leaf in the center works the disconnect and the leaf on the right works the grip safety.
To test the setting of the disconnector leaf of the sear spring, Install only the trigger, magazine catch, disconnector, disconnector/ sear pin, sear spring and mainspring housing into your bare frame. Notice that when you pull on the trigger, you are feeling spring tension from the center or disconnector leg of the sear spring.
Clamp the frame in your bench vise with the frame rails level with the top edges of the jaws. Use a Trigger Pull Gauge to measure the disconnector spring tension. Pull the Trigger Pull Gauge to the rear, until the disconnector just begins to move and read the Gauge. Adjust the tension of the center leg of the sear spring by bending the spring leaf above the pivot point at the mainspring housing. Bend the spring outward to create less spring pressure, bend it inward to create more spring pressure.
When I bend the legs, I do it with my fingers, no pliers, vise or mechanical device. I make the bend over the length of the leaf and avoid making a kink. Before bending, I look at the sear spring from the left-hand side, so I can see and note the relationship between the left and center leafs. You might find it useful to take a cell phone picture showing the relationship between left & center leaves, each time you adjust. Bend a little and then compare. As soon as I can see a difference, I set the parts back up in the frame and retest the pull weight. Repeat as needed. Be aware that if you overwork the spring by repeated or extreme bending, you can kill it as a good spring.
Adjust the spring pressure until you get a reading of 12-14 oz. Pull rearward on the trigger with the Trigger Pull Gauge only far enough to cause the disconnector leg to move. Note that if you pull the gauge too far, you will also engage the sear spring leg and that will give you a false reading on the trigger pull gauge.
After the center leaf is adjusted correctly, add in the sear to the limited assembly. Again, pull to the rear with the Gauge and read the spring pressure with the Trigger Pull Gauge just as the sear begins to move. We now need a total of 26-28 oz. of spring pressure with both the disconnector and sear legs of the sear spring engaged. If you get a reading that is different than what you want, bend the sear leg of the spring in or out until you get the 26-28 oz. reading. If I need a heavier trigger pull I adjust the tension of these two spring legs upward. Remember, both legs of the sear spring need to be adjusted equally.
The last item of sear spring tuning is setting adequate tension on the grip safety to return it to it’s engaged position. There is no specified force for this, just enough to keep the grip safety effectively pushed out, when the hand is off the grip. A good rule of thumb is enough force so it doesn’t rattle when you hold the gun by the slide and shake it.
When you are satisfied with your trigger pull, perform the normal bench tests to check for disconnector operation, trigger bounce, hammer follow. If those results are satisfactory, when you range test, load only two rounds in the pistol to begin with to test for correct operation, then try three four and so on. This is a precautionary safety measure were the gun to fire out of control.