Gus Norcross, originally trained on National Match rifles and pistols by the National Guard Marksmanship Training Unit specializes in Garands, M14s and 1911s at his small shop on the coast of Maine. His website is www.angusarms.com. He will be offering gunsmithing tips and tricks on Fridays.
"Overtravel" is movement of the trigger beyond what is actually necessary to release the sear. Many aftermarket triggers and an increasing number of factory pistols are supplied with a small stop screw located in the lower half of the trigger which contacts the magazine catch to limit trigger movement. Incorrect adjustment of this screw allows the hammer safety notch to hit the sear nose when the pistol is fired, possibly damaging the engagement surface of the sear.
Checking the adjustment is simple. I usually remove the slide assembly for better control of the hammer. Hold the trigger to the rear and grasp the hammer with your non-firing hand. Rotate the hammer through its normal arc of movement, feeling for any interference with the sear. If you feel the hammer bump the sear, back out the screw a quarter turn at a time until no contact is felt. If you don't feel contact, turn the screw in until you do and then back out the screw a quarter- to a half-turn for clearance.
On Colt Series 80 pistols, extra overtravel is necessary to raise the firing pin block high enough to allow free movement of the firing pin. Once the adjustment is set you might want to stake or Loctite the screw to prevent it from backing out.
Overtravel adjustment screw
The overtravel adjustment screw is located in the bottom half of the trigger. It can be turned with a hex key while still installed in the frame.
The overtravel screw protrudes from the rear of the trigger and stops against the magazine catch. (Parts removed from the pistol for clarity)
Rotating the hammer
Hold the trigger to the rear while rotating the hammer through its normal arc of movement. You should feel no bump of the sear against the hammer notch.
Adjust the screw
Adjust the screw a quarter-turn at a time until you feel no hammer bump. Series 80 pistols will need extra overtravel to activate the firing pin safety.