I recently used this handy guide developed by Jack Weigand and hosted by Brownells to tune my new STI Spartan from a stock 5-ish lbs to a crisp 2lb, 12 oz with only tuning the tension of the sear spring. This guide goes into other detail of how to tune various aspects of the gun, but in the section titled "Sear Spring Prep", he details the steps anyone can perform to fine tune the pull weight of your trigger to you liking. If your trigger break is already fairly crisp and clean, this modification will help pull the weight down to any particular weight you dictate with the amount of tweaking you can do. You will need 1 particular tool that isn't common and that's a trigger pull weight scale so you can measure the tension of the various legs of the sear spring.

 

http://www.brownells.com/.aspx/lid=10297/GunTechdetail/2-lb-Trigger-Pull?source=CJ

 

SEAR SPRING PREP — The adjustments that I make to the sear spring are the only variables I use to determine final trigger pull weight. The lighter I set the sear spring, the lighter the final pull weight and vice versa.

 

The 1911 Auto sear spring is a flat spring that has three legs and it works as a return spring for the sear, disconnect and grip safety. When viewed from the rear, the leg on the left works the sear, the leg in the center works the disconnect and the leg on the right works the grip safety.

 

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 an RCBS Trigger Pull Gauge (#747-094-500) to measure the disconnector spring tension. 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.

 

sear and disconnector

Combined sear and disconnector

pull weight shows 16 oz.

 

Adjust the spring pressure until you get a reading of 8 oz. Pull rearward on the trigger with the Trigger Pull Gauge only enough to cause the disconnector leg to move. If you pull it too far, you will also engage the sear spring leg and that will cause you to get a false reading on the gauge.

 

Next, add in the sear to the limited assembly. Again, measure the spring pressure with the Trigger Pull Gauge. We now need a total of 16 oz. of spring pressure with both the disconnector and sear legs of the sear spring engaged. If you get a reading that is either more or less, bend the sear leg of the spring in or out until you get the 16 oz. reading. This is really the only variable I do to my trigger jobs. If I need a heavier weight trigger pull I adjust the tension of these two spring legs upward. Remember, both legs of the sear spring need to be adjusted equally. Here is an example for a 3½ pound trigger pull:

Disconnector Spring Weight - 16 oz.

Sear Spring Weight - 32 oz.

cool, thanks for the info

Very cool, Thanks, Copied and saved for future reverence.