Assembling an AR Lower – Step 5 of 11: Installing the Trigger Assembly

An AR trigger assembly is four parts not including the pin that holds the assembly in the receiver.  I like Palmetto State Armory’s Enhanced Trigger Group that has a polished nickel boron finish for my basic AR builds.  My favorite trigger manufacturer is Geissele and have used a number of their models over the years but they are pricey.  The PSA enhanced trigger is $39.99 and a nice improvement over the normal Mil-Spec trigger.  I should note that even the regular trigger from PSA is not bad.  I have used build kits from others, such as Anderson, where the trigger felt very “gritty” until it wore in whereas the PSA triggers have not had that feeling out of the bag.

So, when you get a trigger group from PSA, as well as most other vendors, they will have the components in a bag. Pour out the contents and organize them to make sure all the parts are there.  Notice I am using a green fabric work mat.  These are made by several companies and the benefit is that the fine nap of the mat softens the impact of small parts so they don’t fly/roll all over the place.  It helps keep stuff from getting scratched up.

In the next photo you will see the trigger and hammer assemblies and all the parts that should be there.  On the left is the trigger assembly – disconnector, trigger pin, small green disconnector spring (note that the vendors do not always color this spring but it is uniquely shaped), the trigger itself and the trigger spring.  On the right is the hammer assembly and starting at the top you have the hammer pin (the pins are identical by the way), the hammer itself and the hammer spring.

Even though this trigger is polished, I polish the mating surfaces to a mirror finish with a Dremel, felt wheel and a fine polish such as Flitz.  I also remove any burs/rough endges that I encounter with a fine stone. I don’t change the geometries – my goal is just to get things nice and smooth.  Note, if you skip this the trigger will need to wear in to smooth out.

Next, install the trigger spring.  Note the orientation of the front of the spring under the nose of the trigger:

Now if you look at the disconnector spring and you will notice that one end is wider.  You push it down into the round pocket that is machined in the back of the trigger.


Now you have an option that will make your life way easier – assemble the trigger group outside of the receiver using a slave pin.  I’m just going to talk about modern ARs and not all the ban-era Colt hijinks or oversize pins for worn rifles.  In general, the trigger and hammer pins have a diameter of 0.154″.  This is the same size as a #23 drill bit. You can go, buy a cheap bit, cut the shaft off so the length of the pin is the same as the width of the trigger.  I would recommend using sandpaper to round the edges of the pin so you wind up with the following:

You can function test the disconnector and make sure that it smoothly rocks back and forth with the spring supporting it.

Now, if you do not want to go the pin route, you will need to juggle everything in the receiver but I would still recommend using a 9/64″ or 1/8″ pin punch to help line things up from the right side as you are looking down at the receiver.  They are smaller than the normal pin so just expect to do a bit more positioning.  This method works fine – it’s just not my personal preferred method any longer.

Ok, so let’s say you did take my advice – now place the trigger assembly down in the receiver with the trigger facing forward.  Put some pressure on the top of the trigger assembly with your thumb, line up the slave pin with the hole and push in the real trigger pin from the left to the right.  Note how I have the groove on the left side – one of the hammer spring’s legs will lay in that groove and lock the pin place.  Now it just becomes a matter of wiggling thins around and pushing the pin all the way through.  Be sure to catch your slave pin before it falls out.  This does not take a ton of force.  If the pin isn’t going in all the way and things are lined up properly, use a rubber or plastic faced mallet to tap it in.


Once installed, squeeze the trigger and make sure to is going back and forth with the spring.  Double-check also that the disconnector rotates also.  In both cases you should feel the springs doing their job.

So you now have the trigger installed and next up is the hammer!

If you find this post useful, please either buy something using one of the links to eBay and Amazon.  With Amazon, if you click on one of our links and then buy something else – even unrelated stuff like clothes, electronics and groceries – we get credit and it would be hugely appreciated.  Doing something like the above will help us fund continued development of the blog.

Rotary Tool Dremel Accessory Kit 228 PC | Grinding Sanding Polishing

End Date: Sunday Feb-16-2020 14:02:08 PST
Buy It Now for only: $17.95
Buy It Now | Add to watch list

Dremel 8220-DR-RT Performance Variable Speed Rotary Tool Kit Reconditioned

End Date: Thursday Feb-6-2020 9:41:05 PST
Buy It Now for only: $68.50
Buy It Now | Add to watch list

350pcs Rotary Tool Accessories Bit Set Polishing Kits For Dremel New

End Date: Wednesday Feb-26-2020 19:35:16 PST
Buy It Now for only: $15.99
Buy It Now | Add to watch list

Felt Polishing Buffing Pads Wheel Wool Plastic Dremel Rotary Tool Kit Set 20Pcs

End Date: Sunday Feb-23-2020 18:40:43 PST
Buy It Now for only: $6.95
Buy It Now | Add to watch list

129 Soft Felt Polishing Buffing Wheel Mixed Set Accessory for Dremel Rotary Tool

End Date: Monday Jan-27-2020 14:15:18 PST
Buy It Now for only: $10.97
Buy It Now | Add to watch list

134Pc Rotary Tool Dremel Accessory Set Kit Sanding Polishing Cutting 1/8" Shank

End Date: Monday Feb-3-2020 14:46:24 PST
Buy It Now for only: $11.25
Buy It Now | Add to watch list

88Pcs/Set Wool Felt Polishing Buffing Pads Waxing Head Wheel Dremel Accessories

End Date: Thursday Jan-30-2020 16:43:43 PST
Buy It Now for only: $8.29
Buy It Now | Add to watch list

40-Piece Dremel Rotary Tool Accessories Kit Grinding Polishing Shank Craft Bits

End Date: Monday Jan-27-2020 13:18:14 PST
Buy It Now for only: $13.90
Buy It Now | Add to watch list

228pc Dremel Rotary Tool Kit Grinding Polishing Shank Craft Bits

End Date: Tuesday Feb-11-2020 0:32:40 PST
Buy It Now for only: $16.98
Buy It Now | Add to watch list

129 Pcs Wool Felt Buffing Polishing Pad Wheel Cone Tips Bob For Grinder Dremel

End Date: Monday Jan-27-2020 13:07:37 PST
Buy It Now for only: $10.97
Buy It Now | Add to watch list


(Visited 110 times, 1 visits today)

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.