Trigger Tuning Tips

by Bob Londrigan as published in Front Sight Magazine, July 2004

If you have ever had the pleasure of pulling the trigger on a gun with a really good trigger job, then you know the feel.  Sometimes described as a glass rod breaking, what you are feeling is the result of a near frictionless movement of the sear across the hammer hooks.  To get this feel all components must fit together with precision and there cannot be drag anywhere in the trigger system. If these words do not describe your trigger pull, then the information in this article may help you out.  My intent here is not to teach you how to do a trigger job, rather to explain how certain adjustments can affect the feel and reliability of your trigger.  This information will also enable you to give a pistolsmith feedback on exactly what you want in a trigger job.  One quick but very important disclaimer -- before you get started performing any maintenance, always double check to make sure your gun is unloaded.

The full cycle of a trigger pull consists of four phases.  Phase one, the pre-travel (often called “take-up”), is the distance the trigger travels at the beginning of the pull before it engages the sear.  Phase two, sear movement, is the trigger causing the sear to move until it clears the hammer hooks.  Phase three, overtravel, is the distance that the trigger travels from the time the hammer releases until its travel is stopped by contact of the overtravel screw with the magazine release.  Phase four, reset, is the distance your trigger must travel forward before you can again pull the trigger.  We will examine each of these phases and look at some of the adjustments you can make to improve your trigger job.   

Phase One:  Pre-Travel

Before considering any type of adjustment to your pre-travel, begin by measuring the amount of pre-travel you currently have.  Use a caliper to measure the distance between the trigger and the triggerguard.  Then move the trigger back until it contacts the sear and measure again. The difference between these two measurements is your pre-travel.  You need at least 0.025-inch pre-travel or your half-cock notch will not function.  Some guns may need as much as 0.040 inch.  

If you think you have too much or too little, the pre-travel can be adjusted on most triggers by bending the adjustment tab on the front of the trigger bow. Bend the tab forward slightly to reduce the amount of pre-travel; bend it back a little to increase the pre-travel.  After you’ve made an adjustment, always check to make sure that your half cock notch still works.  To do this, use your thumb to slowly lower the hammer to halfcock and then pull the trigger.  The hammer should not drop.  If your gun fails this test, you either need more overtravel or there may be damage to the half-cock notch or sear.  Be sure to fix the problem, as this is a safety feature that must function on your gun.  At a match, this is checked at the chrono stage.

The amount of spring pressure that is applied during pre-travel is something else you’ll want to look at.  Some people prefer a lot of return pressure while others prefer that it be light.  If you’re after a very light trigger pull, then a light return pressure will enable you to have more pressure on the sear (left) leg of the spring.   A good rule of thumb is to have about 1/3 of the total trigger pull poundage on the return spring.  For example, with a two-pound (32 oz.) trigger pull, you want about 11 ounces on the return.  I personally prefer around 6 oz. for my 1½ lb trigger pull.  I encourage you to not going any lighter than this as too little pressure on the return makes your trigger susceptible to hang-ups from dirt and grit.  Use a trigger-pull gauge to determine the poundage required to move the trigger through its pretravel.   If necessary, adjust the return pressure by bending the middle leg on the sear spring.

Phase Two:  Sear Movement

The most important thing during phase two, sear movement, is that you cannot feel the sear move as you pull the trigger.  “Trigger creep” is when you can feel the sear moving across the hammer hooks.  Proper angles smoothly cut on the hammer and sear will result in a trigger that breaks crisply and cleanly.  Sear movement should be adjusted only by a competent pistolsmith.  He can modify the angles on the sear and hammer, the amount of breakaway cut on the sear face, and the height of the hammer hooks. 

Phase Three:  Overtravel

Phase three, overtravel, will initially be set at the optimal level by your pistolsmith.  However, this amount of overtravel may change over time as trigger components wear or if the overtravel screw moves.  That’s why it’s a good idea to periodically check the amount of overtravel on your trigger.  Too little overtravel can cause malfunctions such as light primer strikes or, in the worst case, can keep you from being able to pull the trigger.  To test if you have enough overtravel, hold the hammer back, pull the trigger, and slowly rock the hammer back and forth.  You should not feel contact between the hammer and sear.  If you do, add a little more overtravel by turning the overtravel screw out a little.  Out is counterclockwise if you are looking at the gun from the muzzle end. 

Too much overtravel is not really a problem as it simply increases the reset distance.  This is the distance your trigger has to move before you can pull the trigger again.  To decrease the amount of overtravel, turn the overtravel screw in a little (clockwise).   Some people like a little extra overtravel as they claim it prevents them from jerking the trigger.

Phase Four:  Reset

As I just explained, the reset of your trigger pull is the distance your trigger must travel forward before the disconnector clicks up and enables you to pull the trigger again.  Although this is mainly a function of overtravel, it is also impacted by the sear/hammer geometry.  To measure the reset, first pull the trigger and then rack your slide.  Now measure how far the trigger must travel before you hear the disconnector click and reset. Most guns need at least 0.030-inch reset.  Adjusting your overtravel as explained above also adjusts your reset.

In addition to examining each of the four phases of your trigger pull, there are several other things you can check to make sure everything is right with your trigger. There should be no drag on the trigger or trigger bow.  Check this by dismantling your gun to the point where there is nothing touching the trigger.  Now tilt the gun back and forth. The trigger should move back and forth on its own with no drag.  If there is some drag, clean out any dirt or powder residue that may have accumulated.  Also look at your thumb safety engagement (something else that is checked at the chrono).  To check engagement, cock the hammer, apply the thumb safety, and then pull the trigger. You should not see the hammer move.  This is easier to evaluate if you perform the test with the grip safety removed and also watch the sear while you pull the trigger.  Next, take the safety off.  The hammer should not fall.  If the hammer moves or falls during either of these tests, then you do not have enough engagement between the safety and the sear.  This must be corrected before using the gun.  

Once you have your trigger functioning well, you can make some of these adjustments to see if you prefer one setting over another.  Eventually you’ll determine what works best for you.  Then the next time you have a gun built or a trigger job done, you’ll be able to effectively communicate your trigger needs to your pistolsmith.  Another option is to try one of the pre-tuned trigger groups available in the market.  Here the individual trigger components have already been cut or set up with the appropriate angles.  Or, if all this sounds too complicated, find a pistolsmith whose trigger jobs are perfect for you and rely on him make the best decisions on trigger components and settings.

The perfect trigger group to start with: Click here for more info on this trigger group

 

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