How To Install an AR Trigger

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MistWolf

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Installing an AR trigger can at first be a bit puzzling, but with a little guidance, it’s quite simple and straight forward. The trigger featured in this install is a Geisselle SSA-E, but the procedure is no different from any standard AR trigger.

The G trigger group came as two sub-assemblies, trigger and hammer. Also included was a slave pin. The slave pin is just long enough to hold the trigger and disconnector together.

NOTE: Prior to installation, lube all sears, pivot points and the bottom curve of the hammer with clean grease. Any clean grease will do. A lubed AR trigger is a happy AR trigger.
Click to expand...

View attachment 803301

The trigger sub-assembly of the SSA-E comes with the trigger pin installed. The slave pin is used to temporarily replace the trigger pin and hold the disconnector in place during installation. If you don’t have a slave pin, make one from a spare trigger pin or the correct size drill stock. Hang on to it for future trigger installations.

View attachment 803302


Push the trigger pin out with the slave pin

View attachment 803303


until the slave pin fits evenly on both sides of the trigger sub-assembly.

View attachment 803304


Set the selector to the FIRE position. Carefully place the trigger sub-assembly in the trigger housing of the lower receiver. Tip it so the tail slips under the selector. Make sure the legs of the springs point forward and rest on the receiver on either side of the trigger cut-out.



NOTE: Trigger and hammer pins are interchangeable. They have grooves cut in the middle and the end. The groove at the end is for the hammer spring legs to lock the trigger pin in place, preventing it from drifting out. The groove in the middle is for the hammer J pin. The J pin locks into the middle groove to keep the hammer pin from drifting out.
Click to expand...
View attachment 803305


Press the trigger sub-assembly down until the slave pin lines up with the trigger pin hole

View attachment 803306


Then carefully press the trigger pin into place. It will push the slave pin out the other side. The trigger pin can be pressed in from either side of the receiver. The pin should slide into place with just finger pressure.

View attachment 803307


NOTE: Both legs of the hammer spring must rest on the trigger pin. If one or both legs are not resting on the trigger pin, the trigger will not function correctly.
Click to expand...


Next, install the hammer. If the hammer pin is installed in the hammer, remove the pin prior to hammer installation. The slave pin is not needed to install the hammer.


Carefully press the hammer into place. Make sure both legs of the hammer spring are resting on the trigger pin. Press the hammer down until the pin hole in the hammer lines up with the pin hole in the lower receiver.

View attachment 803308


Press the hammer pin until it is in the hammer pin hole but no further. The pin may need a light tap with a small hammer and a brass punch. Do not try driving the hammer pin all the way through.

View attachment 803309


Pressure from the hammer spring will keep the pin from aligning with the pin hole on the opposite side of the receiver. Flip the receiver, grasp the hammer and use it to line up the holes. Once aligned, the pin should slide into place with finger pressure.


NOTE: If the end of the pin is pressed against the inside of the receiver, it will create enough binding that the hammer cannot be lined up. Make sure the pin isn't causing binding.
Click to expand...

View attachment 803310


This is what the pins will look like once everything is in place

View attachment 803311


Here is what the Geisselle SSA-E trigger looks like installed!

View attachment 803312


Once finished, assemble the upper to the lower and test for proper functioning. DO NOT DRY FIRE ON AN UNASSEMBLED LOWER! The hammer striking the lower could cause damage.


Once you understand how and with the right tools, installation of an AR trigger is a breeze. It can be installed without a slave pin, but lining up the trigger and disconnector without it can be frustrating. Don’t forget the grease!
 
Agreed. Too many first-time AR buyers get a stock rifle. Obviously, it will be upgraded. Optics, furniture, and the trigger are the big 3. The first 2 are straightforward, but the FCG is much easier with a visual on spring orientation and such.
 
Nicely done. Great guide for those who haven't done it before. That'll help a lot of people.

Mark
 
Thanks guys. After all the help I've received from folks on this forum and others, I feel it's the least I could do to help those new to the AR family of weapons. It's not the first guide to trigger installation posted on the internet, but I did what I could to keep it clear, concise and easy to search for.
 
Nice briefing and pics. Very nice. A couple of points / options:

Trigger / hammer can be manipulated without the upper if the individual prevents the hammer from striking the receiver by holding the hammer back enough with fingers when pulling trigger,

install a hammer drop block

A thick piece of material, leather, etc wedged at point where hammer would strike rcvr

Other

For hammer / trigger alignment, punches, hex wrenches, etc can be used when installing / removing pins.

Other steps which may be required or make the task easier (based on lower machining, FCG components) include loosening or removing the pistol grip*,

Removal of selector switch

"cocking" the hammer.

If removal of pistol grip is necessary, beware the small spring /detent located near front top of pistol grip. The spring / detent push upward against the selector switch / safety. Easy to fly out and get lost. When reinstalling the grip, make sure the small spring does not get crimped, bent, etc.
 
You can usually get the selector switch out (if you have to to remove or install a trigger) without taking the pistol grip all the way off. Just remove the long machine screw that retains the pistol grip and pull it down the receiver stud enough to release spring pressure on the selector switch detent without freeing the spring and detent.

The most common mistake I have seen (and personally encountered) with installation of AR hammers and triggers is accidentally reversing the orientation of the hammer spring, which is easy to do. Make careful note of the orientation in the photo. Reversing the orientation of the hammer spring makes the hammer easier to install. But doing so reduces the spring pressure on the hammer. This can lead to light primer strikes and misfires, of course. But in some cases it can cause the hammer to get slapped back so quickly by the bolt carrier that it gets knocked back forward before the disconnector can capture it. This can cause doubling or even full auto fire.
 
imashooter said:
Nice briefing and pics. Very nice. A couple of points / options:

Trigger / hammer can be manipulated without the upper if the individual prevents the hammer from striking the receiver by holding the hammer back enough with fingers when pulling trigger,

install a hammer drop block

A thick piece of material, leather, etc wedged at point where hammer would strike rcvr

Other

For hammer / trigger alignment, punches, hex wrenches, etc can be used when installing / removing pins.

Other steps which may be required or make the task easier (based on lower machining, FCG components) include loosening or removing the pistol grip*,

Removal of selector switch

"cocking" the hammer.

If removal of pistol grip is necessary, beware the small spring /detent located near front top of pistol grip. The spring / detent push upward against the selector switch / safety. Easy to fly out and get lost. When reinstalling the grip, make sure the small spring does not get crimped, bent, etc.
Click to expand...


There is also, IIRC, a spring under the grip for the rear takedown bolt that wants to push out. I just put a nicer pistol grip on my LR308 Sunday, so I recall that little bugger. Neither one is hard to deal with, but they shouldn't be bent, and work in a flat, clear area so nothing rolls off into shagcarpet, or under a table, or into a 6th dimensional twilight zone .... still missing a few socks there from 1987.
 
pblanc said:
The most common mistake I have seen (and personally encountered) with installation of AR hammers and triggers is accidentally reversing the orientation of the hammer spring, which is easy to do. Make careful note of the orientation in the photo. Reversing the orientation of the hammer spring makes the hammer easier to install. But doing so reduces the spring pressure on the hammer. This can lead to light primer strikes and misfires, of course. But in some cases it can cause the hammer to get slapped back so quickly by the bolt carrier that it gets knocked back forward before the disconnector can capture it. This can cause doubling or even full auto fire.
Click to expand...

I built an AR lower for the first time recently and the backwards hammer spring got me. Built the firing group, pulled the trigger, and there was no tension under it. Having a factory-built lower to compare to was helpful in seeing where I'd gone wrong.

In general, with building a lower, I found that the only real "tricks" involved with it were

-hammer/spring orientation
-fitting in the front detent (and boy was that a trick - I ordered an extra detent and spring along with my LPK in anticipation of this being hard and ended up needing both of them).
-being careful hammering the trigger guard pin to not snap off the "ears".

Everything else was pretty straightforward. I could look at a Youtube video or PDF to tell me what to do, eyeball my parts and the lower, and everything fit together about the way you'd think it would.
 
Tommygunn said:
There is also, IIRC, a spring under the grip for the rear takedown bolt that wants to push out. I just put a nicer pistol grip on my LR308 Sunday, so I recall that little bugger. Neither one is hard to deal with, but they shouldn't be bent, and work in a flat, clear area so nothing rolls off into shagcarpet, or under a table, or into a 6th dimensional twilight zone .... still missing a few socks there from 1987.
Click to expand...

The takedown pin detent pin and spring are retained by the receiver end plate, not by the grip.
 
pblanc said:
You can usually get the selector switch out (if you have to to remove or install a trigger) without taking the pistol grip all the way off. Just remove the long machine screw that retains the pistol grip and pull it down the receiver stud enough to release spring pressure on the selector switch detent without freeing the spring and detent.

The most common mistake I have seen (and personally encountered) with installation of AR hammers and triggers is accidentally reversing the orientation of the hammer spring, which is easy to do. Make careful note of the orientation in the photo. Reversing the orientation of the hammer spring makes the hammer easier to install. But doing so reduces the spring pressure on the hammer. This can lead to light primer strikes and misfires, of course. But in some cases it can cause the hammer to get slapped back so quickly by the bolt carrier that it gets knocked back forward before the disconnector can capture it. This can cause doubling or even full auto fire.
Click to expand...

If you push firmly on the right side of the safety with your thumb while slowly rotating it from safe to fire you can get the detent to ride up on the barrel of the safety. The safety will move to the left slightly. Don't let it go to far to the left but with the detent riding on the barrel (instead of the groove it's supposed to) you can flip the safety past fire to where Auto would be. You can remove the safety this way but its a pain to put back without removing the grip. Once rotated to the Auto position the flat on the safety will be to the front. I have never found a trigger I could not install or remove once with the safety in that position. Saves messing with loosening the grip to removing the safety. Remember to move it back to Fire before trying to install the hammer.
 
mcb said:
If you push firmly on the right side of the safety with your thumb while slowly rotating it from safe to fire you can get the detent to ride up on the barrel of the safety. The safety will move to the left slightly. Don't let it go to far to the left but with the detent riding on the barrel (instead of the groove it's supposed to) you can flip the safety past fire to where Auto would be. You can remove the safety this way but its a pain to put back without removing the grip. Once rotated to the Auto position the flat on the safety will be to the front. I have never found a trigger I could not install or remove once with the safety in that position. Saves messing with loosening the grip to removing the safety. Remember to move it back to Fire before trying to install the hammer.
Click to expand...
Thanks for the tip. I will give that a try next time.
 
The only thing held in by the grip is the selector detent and spring.

Unless your particular AR-15 is the only one of its kind in the history of AR’s.
 
There's actually a couple of lowers where the rear pin detent is accessed by removal of the pistol grip, similar and in proximity (to the left) to selector spring.
 
Varminterror said:
The only thing held in by the grip is the selector detent and spring.

Unless your particular AR-15 is the only one of its kind in the history of AR’s.
Click to expand...
DPMS LR-308 (DPMS patterned AR-10) uses the grip to retain both the safety-selector and rear take-down pin detents and their associated springs.
 
fitting in the front detent (and boy was that a trick - I ordered an extra detent and spring along with my LPK in anticipation of this being hard and ended up needing both of them).

Use a slave pin to install pivot pin detent and spring, line up holes, drop in spring and detent, use small punch to push detent low enough to rotate slave pin, then push out slave pin with pivot pin

KIMG0112.JPG View attachment 803609
 
Varminterror said:
The only thing held in by the grip is the selector detent and spring.

Unless your particular AR-15 is the only one of its kind in the history of AR’s.
Click to expand...

:confused: Ok .... I was actually refering to a DPMS LR308 .... but I assume it would be the same.
I'm not going to remove the grip to check .... so I hope you don't mind if I stop worrying about it.:ninja:

Edit: Oooooops, MCB and Imashooter got there before me.:oops:
 
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