The stock Glock trigger is very easy to manage and is conducive to accurate shooting. That said, many shooters transitioning from single-action pistols have difficulty adapting to Glock's Safe Action system. Additionally, the mass-produced stamped metal parts and slightly varying tolerances found in the Glock fire control system can result in a significantly different trigger "feel" from one stock Glock to the next. Fortunately, there are ways to customize or improve a Glock's trigger action simply by reconfiguring or working with the stock parts, rather than replacing them with expensive aftermarket parts that may render the gun unsafe.
The Trigger Bar - the serrated trigger face found on the compact and subcompact Glocks may be replaced with the smooth trigger found in the larger-frame pistols. Some find the smooth trigger to provide a more comfortable, positive contact between the trigger face and trigger finger. Note that the trigger is permanently attached to the trigger bar, so the whole assembly must be replaced. Additionally, the vertical extension of the trigger bar (which bears against the firing pin safety) and the rear "slope" (which bears against the connector) may be lightly polished to remove machining imperfections and generally smooth the trigger pull (see "Trigger Job in a Can" below).
The Trigger Spring - the standard Glock trigger spring is a coil-type unit that, when paired with the standard connector (see below), yields a nominal trigger pull of 5.5 lbs. This spring may be replaced with either the NY1 or the NY2 spring to create a heavier, more consistent (ie revolver-like) trigger pull of 8 or 12 lbs., respectively.
The Connector - this is an angled metal piece against which the trigger bar bears, creating resistance and giving the trigger pull much of its weight. The standard connector is unmarked. There is also a "-" or competition connector which results in a trigger pull of about 3.5 lbs. when used with the standard spring. This is the stock setup in Glock's 17L, 24, 34 and 35 competition pistols, but is generally regarded as too light for duty or self-defense use. Also available is the little-seen "+" connector, which produces a pull of roughly 8 lbs. with the standard spring. This is commonly found in police duty guns, and the feel is similar to that produced by the standard connector paired with the NY1 spring.
Using these three main components in various combinations, it is possible to greatly alter the trigger feel of a Glock pistol without sacrificing any of its safety or reliability properties, or voiding the factory warranty. WARNING! NEVER combine the NY1 or NY2 springs with the "+" connector! The resulting trigger pull may be too heavy to engage, or other reliability problems may arise.
The Carry Trigger - My preferred trigger configuration for a carry Glock is what I call the "carry trigger" (catchy name, huh?). It is really nothing more than a NY1 spring paired with a "-" connector. This combination provides resistance from the beginning, eliminating the initial slack or "dead space" found in the stock Glock trigger pull. This results in a more consistent, DAO-type feel, similar to my Kahrs or a tuned DA revolver. The NY1 spring also gives a more positive trigger reset which allows faster followup shots. Finally, the "-" connector eliminates much of the weight added by the NY1 spring, keeping the pull weight to somewhere near stock (about 3/4lb. heavier, instead of some 3lbs. heavier with the NY1 alone). The only real downside to this arrangement is that the NY1 spring returns the trigger so energetically that it may "slap" the trigger finger a bit, causing finger fatigue or even blistering during extended (several hundred round) shooting sessions.
Reduced-Power Striker Spring - This part from Wolff Gunsprings reduces the force that cocks and releases the striker, lightening both take-up pressure and trigger break pressure by approximately one pound. The resulting pull is much smoother and lighter, but does not come without a cost! Lighter spring pressure means the striker is propelled forward with less velocity, and therefore it may lack sufficient force to detonate harder primers (military surplus, CCI, etc). For this reason, this part is intended for use in competition pistols and is not recommended for duty or carry weapons! If your Glock pistol is used for both defensive and competition purposes, you may want to purchase a separate firing pin assembly with the reduced-power spring installed. That way you can just drop in the "competition" assembly prior to a match, and reinstall the "carry" assembly afterward. If you insist on carrying a defensive weapon with a reduced-power spring installed, do so only after extensive testing with various types of ammunition, and use only ammunition with which the pistol has proven reliable!