Trigger Problems: Hammer Follow, Light Strikes, Failures to Reset and How to Fix Them
Most AR-15 trigger problems announce themselves the same way: the rifle does something the shooter did not ask for, or fails to do something they did. A hammer that follows the bolt home, a trigger that will not reset, a primer that was struck but did not fire, or two shots from one press are all trigger problems with mechanical causes and mechanical fixes. This guide takes each symptom in turn, explains what is happening inside the lower, and sets out the fix, along with the point at which the right fix is a new trigger.
First, the safety rule
Any trigger that fires more than one round per press, follows the bolt or fires when the safety is applied is unsafe and the rifle must be unloaded and not fired again until the fault is found. A malfunctioning trigger that doubles is not a feature and is not lawful to leave in that condition; it is a broken part, and a broken semi-automatic trigger that fires more than once per pull can put the owner in a serious legal position. Fix it or replace it before the rifle goes back to the range.
Hammer follow
Hammer follow is when the hammer follows the bolt carrier forward instead of being caught by the disconnector or the sear, so the rifle fails to fire on the next press or, worse, fires as the bolt closes. The cause is almost always a disconnector that is not catching the hammer: a worn or chipped disconnector hook, a disconnector spring that is weak or was installed upside down, a hammer hook that is worn, or a trigger pin that has walked and changed the geometry. Check the disconnector spring first; its wide end goes down into the trigger. Then inspect the disconnector and hammer hooks under a light for rounding or chips. Replace worn parts as a set; a new disconnector on a worn hammer will follow again. On a cassette, hammer follow after installation usually means the housing is rocking; tension the set screws.
Doubling
Two shots from one press is hammer follow that happened to fire, and the causes are the same, with two additions: a hammer spring so light that the hammer bounces off the sear, and a trigger that was filed or stoned by a previous owner until the sear engagement is too shallow. A rifle that doubles is unsafe and must be stopped. If the trigger has been modified by hand, replace it; there is no reliable repair for a stoned sear.
Failure to reset
The trigger stays back or mushy after a shot and the rifle will not fire again until the trigger is released fully or the action is cycled. Causes are a trigger spring installed with its legs behind the trigger instead of in front, a disconnector spring that is too weak or missing, a cassette housing that rocks, a trigger pin that has walked, or a selector that is dragging on the trigger. Check the trigger spring's legs, then the pins, then the cassette tension. On a two-stage trigger, a failure to reset into the second stage is usually a disconnector adjustment covered in the maker's instructions.
Light strikes
A dented primer that did not fire means the hammer did not hit hard enough. The causes are a reduced-power hammer spring, a hammer spring installed backwards, a cassette set to a very light tension, a striker channel in the bolt carrier packed with lubricant or fouling that slows the firing pin, or a firing pin that is worn short. Check the ammunition first; some military-primer ammunition needs a full-power hammer. Then clean the bolt carrier's firing pin channel dry and check the firing pin's protrusion. If the trigger has a reduced-power spring, put the full-power spring back; a light trigger should get its weight from geometry, not from a weak spring.
Walking pins
Trigger and hammer pins that migrate out of the receiver under recoil change the geometry and cause every symptom above. On a mil-spec trigger the hammer spring's legs rest on the trigger pin and hold it; if the spring is installed wrong the pin walks. On a cassette the housing must capture the pins or anti-walk pins must be fitted. Check the pins after every range trip until you are sure they stay.
Out-of-specification receivers
A lower with pin holes drilled slightly off, a rough floor or a shallow selector detent hole will fight any trigger. Symptoms are a cassette that will not seat flat, a trigger that binds, or a selector that will not move with the hammer cocked. Try a known-good mil-spec trigger in the receiver; if it also misbehaves, the receiver is the problem and a gunsmith or the maker should look at it.
Gritty pull and creep
Not a malfunction but the most common complaint. A mil-spec trigger with rough sear surfaces feels gritty and creeps before the break. Do not stone or file the surfaces; that is how doubling rifles are made. Replace the trigger with an enhanced mil-spec or a drop-in, as the installation guide describes.
When to replace
- Any sear or hook that shows wear or chipping: replace the group as a set.
- Any trigger that has been filed, stoned or polished by hand: replace.
- Any trigger that doubles after the springs and pins have been checked: replace.
- A cassette that will not stop rocking after tensioning: return it; the receiver or the housing is out of spec.
The pull weight guide explains why weight should come from geometry and not from springs, and the law guide covers why a doubling rifle must be fixed. Browse replacement triggers in the catalogue.
General information, not legal advice. Current as of September 2026. Laws change; check the official source before you act.
